PLATINUM METALS REVIEW · jections of cis-dichlorodiammineplatinum(I1) at a level (8 mg/kg) which could almost completely inhibit the growth of the trans- planted tumour, while the

PLATINUM METALS REVIEW

A quurterly survey of reseurch o n the platinum metuls urrd of dwelopments in their applications in industry

V O L . 1 5 A P R I L 1 9 7 1

Contents

Some Biological Effects of Platinum Compounds

Surface Phenomena on Rhodium-Platinum Gauzes

'The Electrodeposition of Rhodium on Titanium

Platinum Metals Electrodeposited from Molten Cyanides

Pressure and Thermal E.M.F.s

The Platinum Metals in Organic Syntheses

Abstracts

New Patents

NO. 2

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52

57

58

59

60

68

75

Communications should be addressed to The Editor, Platinum Metals Review

Johnson, Matthey & Co Limited, Hatton Garden, London EClP IAE

Some Biological Effects of Platinum Compounds NEW AGENTS FOR THE CONTROL OF "MOURS

By Barnett Rosenberg Department of Biophysics, Michigan State University

Certain complexes of the platinum group metals exhibit interesting biological efects. At low concentrations some are efective baeteriocides; others stop cell division and force bacteria to grow into long filaments. These complexes can also induce destruction of lysogenic bacteria. Most important, perhaps, some of these complexes are very potent anti-tumour agents against a broad spectrum of tumours, and may shortly be used for cancer Chemotherapy in humans.

In a truly heroic effort the National Cancer Institute of the U.S. Government has screened approximately 140,000 compounds for anti-cancer activity over the past 15 years. Of this number, however, only a dozen or so were inorganic compounds. This imbalance between organic and inorganic compounds reflects a fashion in chemotherapy that started over 35 years ago. Prior to that, heavy metals were extensively used in medical therapy. About 1935, the discovery of the sulfonamides introduced a new class of organic chemicals which were effective against many bacterial infections. Hard on this came the development of the antibiotics which coupled a high degree of efficiency with a low toxicity. At present, excepting a few outstanding drugs, heavy metals and other inorganic chemicals have ceased to be of active interest as chemotherapeutic agents. The screening program of the National Cancer Institute, occurring within the last 15 years, reflects this bias.

Recently a new class of potent anti-tumour agents has been discovered. These are inorganic complexes of the transition metal Group VIIIb. In this article we shall review briefly the history of this new development and discuss some of the properties that are

now known concerning the activities of these compounds. It will be taken as granted that the general reader of this journal will find, as did the author, that biological and medical terminology are "terra incognita". To offset this to some extent, a glossary of the more important terms is appended to the article.

The germinal discovery was made about 1964 when platinum electrodes were used to apply an alternating electric field across a chamber in which bacteria were growing ( I ) . Application of the electric field caused a cessation of all division in the E. coli rods, and since growth was not inhibited, resulted in the appearance of long filaments, A comparison of the normal appearing E. coli rods and the filamentous rods caused by the application of the electric field are shown under the same magnification in Pig. I. Extensive detective work was required before we could conclude that the effective agent in blocking cell division in the bacteria was a small concentration (-10 ppm) of some platinum complex in solution, electrolytically formed by the applied electric field. I t required much further work to determine that these complexes were cis-dichlorodiammineplatinum(I1) and cis-tetrachlorodiammine- platinum(1V) (2,3).

Platinum Metals Rev., 1971, 15, (2), 42-51 42

Fig. 1 l'hasc. rontrnst photomirrogmphs (j" E. roli 11. \ 600. ( 0 ) Aormal bactcria grown i n chornirally rd mcdiuni. ( I ) ) Filanio~atoris bctrterin grown in sume medium but incorporating I 0 p p m I$ ris- orodinniniiiirj~latini~rri( I I ) . The, nbility (tf thr rells to dividr and sc'paratc, 1 9 completely inhibited, so

continiird groibth lrads to long filaments

The structures of these complexes and some chloroplatinum(I1) double negative ions are other differently acting agents are shown in bacteriocides at low concentrations (I to 6 Figs 2, 3 and 4. With the verification that ppm in the bacterial growth medium). These these platinum complexes were indeed compounds undergo photochemical changes capable of selectively blocking cell division in in the bacterial media, leading to a subse- bacteria, a series of investigations was under- quent replacement of first one and then a taken to determine the mechanism and the second chloride by ammonia. The resulting generality of the effect. VanCamp discovered neutral molecules arc not bacteriocides until that the hexachloroplatinum(1V) and tetra- very high concentrations ( - IOO ppm in

cis-dichloro- cis-dibromo- oxalato- diammineplatinum( I I) diammineplatinum( 11) diammineplatinum(I1)

dichloroethylene- cis-tetrachloro- tetrachloroethylene-

I"ig. 2 Stri~rttrrrd j h r i i i l u i , of crrtiur nriti-trtmour comp1ew.s of platinum. Only n vrry f i i ( diamineplatinum( I I) diammineplatinum( IV) diamineplatinum( IV)

sprr

tetraammineplatinurn( 11) all complexes of cis-dichlorodiammine ion platinum(I1) with methionine

Fig. 3 Structural formulae of low toxicity. non-actiur complexes of plat inum. Some soluble salts qf the nwtals are tolerated very zucll i n the animals, indicating that thr activity is not dzc~

to u general hravy metal poisoning

solution) are reached. Interestingly, the trans forms of these neutral molecules are not effective in blocking cell division in bacteria, while the cis isomers are. Thus we have two groups of compounds with different bacterial effects; the negative ionic species which are generally bacteriocidal, and the neutral species, in the cis form, which block cell division, but not growth. Gillard and his co- workers have reported similar effects in organic rhodium complexes (4), and Gale, Howle and Smith (5) have extended these observations to include photochemical reactions in ammonium hexachloroiridate, which also parallel the platinum transformations and bacterial activities.

A third class of bacterial effects of platinum compounds was discovered much later by Keslova (6). I t is known that some strains of

E. coli have previously been infected by viruses (bacteriophages) and that the genetic material of the virus was incorporated into and became part of the genetic material of the bacterial cell. The viral genetic material (genome) is repressed in these cells and is not normally detectable. Such bacterial strains are called “lysogenic” for the simple reason that a number of agents, such as ultraviolet light, X-rays, and some chemicals such as the nitrogen mustards (alkylating agents), are capable of inducing the development of partial or complete viruses which lead finally to the destruction (lysis) of the cell. The platinum compounds which are effective anti-tumour agents were found to be extremely potent in inducing lysis of such lysogenic bacteria.

Fig. 5 exhibits the three types of effects on the growth curves in test tubes of various

rrans-dichloro- tetrachloro- cis-dinitrato- diammineplatinum( 11) platinate(I1) ion diammineplatinum(I1:

oxalatoethylene- diamineplatinum( 11)

4 +

tris(cthy1enediamine)- platinum(I1) ion

b‘ig. 4 Strurturcd formulae of high toxicity, non-active complexes ofplatinum

Platinum Metals Rev., 1 9 7 1 , 15, (2) 44

strains of E. coli reacting to the presence of different compounds of platinum, showing in Fig. 5a the bacteriocidal effect, in Fig. 5b the cell division inhibition, and in Fig. 5c the lytic effects of these compounds.

Anti-tumour Activity Since the platinum complexes of Fig. z are

active in inhibiting cell division in bacteria, it

Platinum Metals Rev., 1 9 7 1 , 15, (2)

suggested that they may also be interesting compounds to test as anti-tumour agents. Such a study was undertaken in our laboratory. We first determined the level of the platinum compounds which would be tolerated by the animals (LD,, doses), and then whether, below these levels, they would inhibit the growth of transplantable tumours in these animals. The first test was with a

45

Sarcoma 180 tumour (a standard test tumour in cancer research) in Swiss white mice. We found that the animals would tolerate single injections of cis-dichlorodiammineplatinum(I1) at a level (8 mg/kg) which could almost completely inhibit the growth of the transplanted tumour, while the LD,, level was 14 mg/kg. This was the first evidence that these complexes are active anti-tumour agents (7). This compound was then submitted, along with cis-tetrachlorodiamminc- platinum(1V) to the National Cancer Institute for screening against the Leukaemia LIZIO tumour in mice, their present standard screening tumour. Their results showed that cis-dichlorodiammineplatinum(I1) has a potent activity against this tumour, producing an increase in life span of the tumoured animals of 380 per cent, and a “cure” rate of 4 out of 10, with single injections at the therapeutic dose, 8 mg/kg.

In addition to inhibiting the development of newly transplanted Sarcoma 180 tumours in mice, it was later shown that one could wait for a period of 8 days for the transplanted tumour to grow to a very large size, before instituting treatment with the cis- dichlorodiammineplatinum(I1). A single injection, intraperitoneally, of 8 mg/kg of this drug caused the complete regression of the large tumours in close to IOO per cent of the animals (8). These results are illustrated in Fig. 6. In addition to producing such extensive “cures” of advanced sarcomas, we found that even up to 11 months afterward, the animals remained immune to a re- challenge with the same tumour. Thus the “cure” produced long-lasting immunity to this tumour system (9).

This first anti-tumour complex of platinum has now been tested extensively on many other transplantable tumour systems. Kociba (10) demonstrated that it can produce 100 per cent “cure” in rats of the Walker 256 carcinosarcoma and the Dunning Ascitic Leukemia. Again, in his studies he has shown that one could wait until the tumour is in a highly advanced state, i.c., four days before the

animal would die, before instituting treatment, and still rescue IOO per cent of the animals. The drug has been tested now at the National Cancer Institute and at the Chester Beatty Institute in London by Haddow and Connors (11) on a number of other tumour systems such as the Lewis Lung carcinoma, the €3-16 melanocarcinoma, the P388 leukemia, and the ADJ-PC6A tumours. It has shown marked effectiveness in all of these tumour systems. The latter group have also shown a lack of activity of the complexes against the Rabbit VX2 carcinoma, the Gardner tumour, and a strain of the Walker 256 carcinosarcoma that is resistant to alkylating agents. At this time, a large number of other laboratories are investigating the anti-tumour activity of these complexes against a host of additional tumour systems. Their results will be reported in the near future. We conclude from this series of studies on the anti-tumour activity of cis-dichlorodiammineplatinum(I1) that it is a very effective agent against a wide spectrum of transplantable tumours in animals. Anti-tumour activity has also been exhibited by the other compounds shown in Fig. 2. In some tumour types, other compounds have been shown to be more effective than the cis-dichlorodiammineplatinum(I1). We have then a new class of drugs which could form a set of specific chemotherapeutic agents against specific types of tumours.

While transplantable tumours form the best screening systems for evaluating the effectiveness of new anti-tumour agents, there are other types of tumour systems which are more relevant to the cancers that occur in human beings. Two other such types of tumours are those caused by injections of chemical agents (carcinogens) into the animal which induce the formation of tumours, and those which are caused by the injections of certain classes of viruses. It is of interest, therefore, to determine whether these platinum complexes are capable of exhibiting anti-tumour activity against carcinogenically or virally induced tumour systems. Recently, Welsch (12) has investigated the activity of


Fi?. h The, rrgrossion of u large Saxoniu-180 turnour in the! Swiss white rnouse by a single intraperitoneul injrction of’ c:is-rlichlorodiarnrnine~Z~itiniini( 11) ut the therapeutic dosc (8 mg/kg)

ci,-dichlorodiammineplatinum(I1) against the dimethylbenzanthracene-induced mammary tumour in the rat. He has reported the complete regression of a very large number of extensively developed mammary tumours in the rats, with at least three out of 14 animals completely “cured” of all tumours. Since this particular tumour is the bcst model system for human mammary tumours, these results are of significant interest. Hinz (13) has tested the same compound against a virally induced tumour of the chicken. The chicks were injected with the Rous Sarcoma Virus, which, after a period of weeks, produces a large Sarcoma tumour in the wing web of the chick. Again, therapeutic doses of the complex were capable of causing complete regression of these tumours in 95 per cent of the animals. From the accumu- lating results of the anti-tumour activity of

some platinum compounds against transplantable, carcinogenically induced, and virally induced tumours we can conclude that these compounds have one of the broadest spectra of action of any class of anti-tumour agents yet discovered. From the fact that it can cause regression of large tumours, and rescue animals when injected a few days prior to their death, we conclude that these compounds are very potent anti-tumour agents.

A major approach of the National Cancer Institute chemotherapy program is the use of combinational drug therapy. The basic idea is to mix drugs, all of which hit the target tumour, but each of which have different side effects. Usually these com- bination drugs have shown enhanced activity over and above the best of the individual drugs involved. However, only very few


combinations have been found which produced synergism of anti-tumour activity. Recently Venditti (14) showed that a com- bination of cytoxan (an alkylating agent) and cis-dichlorodiammineplatinum(I1) produced a large number of “cures” against an advanced leukaemia LIZIO in mice, whereas each of them individually produced only a small percentage increase in the lifespan, even up to toxic doses. This would appear to be a very promising method of treatment, since the drugs are both used at levels where side effects are minimal. I will describe below, in the section discussing the mechanism of action of the drug, a possible rationalisation for the apparent therapeutic synergism of these two drugs.

The Toxicological Effects of Platinum Complexes

Experience teaches that it would be overly optimistic to expect an anti-tumour drug to be so specific in its action that it does not at all affect adversely the normal tissues of the body. In general, one finds that all such drugs have side effects which limit the dose levels that can be used in man. It is essential to predict from animal studies the kinds of toxicological effects one may anticipate when the platinum complex is used in human patients. Such studies have been undertaken in a number of laboratories.

It is first necessary to determine how long the drug remains in the animal after a pulse injection, and also its distribution as a function of time in the various organs of the animal. Toth-Allen (15) has evaluated the distribution in mice using a neutron activation technique which is sufficiently sensitive ( N 0.01 ppm) to measure accurately the low concentration of the platinum complex generally found in tissues (-I to 5 micro- grams per gram of tissue) after injection. She has reported that there is no specific uptake of the platinum complex in the Sarcoma 180 tumour tissue, and that indeed it appears in much higher concentrations in the filtering and excretory organs such as the


liver and kidney. However, the damage to these latter organs is negligible, whereas the tumour, of course, is destroyed. A significant fraction ( - 15 per cent) of the injected drug is still detectable after six days. It has been found, both by Kociba and Toth-Allen, that the drug primarily affects those cells of the body which are most rapidly dividing, such as the cells of the intestinal lining, and of the bone marrow. It is, therefore, a cytotoxic drug, and must be used with caution. These side effects are those generally expected with anti-tumour drugs and techniques for their amelioration have been developed. In the case of the platinum complexes, the damage is always reversible, and the animals recover. They exhibit no long-lasting side effects caused by therapeutic treatment.

The Molecular Biology of Platinum Complexes

The interaction of the platinum complexes with cellular macromolecular syntheses has been investigated by Harder using tissue culture techniques (16). He has measured the ability of treated cells to manufacture nucleic acids (DNA and RNA) and proteins, using radioactively labelled precursors for each of these species. Only those platinum complexes which are active anti-tumour agents are capable of inhibiting the synthesis of DNA. Those which are inactive do not produce such inhibition. Further, at the dose level that appears in the tumour tissues of animals, the DNA replication is selectively inhibited, while RNA and protein synthesis are not inhibited. Similar results have been found by Howle and Gale in vivo (17). Such results are shown in Fig. 7. Harder has further proved that the inhibition of DNA synthesis is not caused by a blockage in the synthesis of the necessary precursors of DNA, nor is the ability of these precursors to enter the cells impaired. We conclude from these data that the platinum complexes most probably act by causing a primary lesion in the DNA of the cell. It is of interest now to determine the nature of this primary lesion.

Ihobnik (IS) suggested, on the basis of the similar occurrence of the two active chloride groups in bifunctional alkylating agents and in the cis-dichlorodiammincplatinum(II), that the platinum complexes act similarly to the bifunctional alkylating agents. Information we have gathered up to now indicates that there is indccd a similarity in the actions of both of these classes of compounds, but it is by no means an idcntity. For example, they are both capable of forcing giant cell formation in mammalian tissue culture, and of forcing filamentous forms in bacteria. They both selectively inhibit DNA synthesis at low concentrations in mammalian cells, and are

very effective in inducing lysogenic strains of bacteria. The present understanding of the action of the bifunctional alkylating agents is believcd to be the formation of an interstrand crosslink between the guanine bases, at the N-7 position, in double stranded DNA. In order to accomplish this interstrand crosslink, the two active chloride groups must be approximately 8A apart. In the cis-dichlorodiammineplatinum(II), the spacing between the two active chloride groups is 3.3A. It would appear, thcrcforc, that such platinum complexes cannot be causing the same primary lesions, i.e., interstrand crosslinking, as do the bifunctional alkylating agents. On the basis of some recent evidence that the platinum complexes inhibit a single stranded bacteriophage as well as it does the double stranded bacteriophage (19); that it reacts in vitro primarily with purine bases rather than pyrimidine bases; and taking into account that the stacking spacing of the bases in the Watson-Crick model of DNA is about 3.4A, we arc led to suggest that the primary lesion caused by the platinum complexes is an intrastrand purine dimer. This is a new type of lesion that has not been investigated before. In vitro studies with purine dimers tend at this time to validatc this hypothesis, but much further work must be done to prove or dis- prove it.

If indeed the platinum complexes do form an intrastrand purine dimer, while the bifunctional alkylating agents form an interstrand crosslink, it may then be that a ccllular repair mechanism, which normally operates within the cell to eliminate lesions in the DNA, would have more difficulty in simultaneously repairing both types of lesions, than either one of them individually. This could provide a rationale for the therapeutic synergism described above.

Speculation on the Mode of Action of the Anti-tumour Effects

Reslova (6) has shown that all platinum complexes which are active anti-tumour agents are capable of inducing lysis in lyso-


genic bacteria; those which are non-active do not produce such lysis. These results provide a clue as to the mode of action of the platinum complexes in specifically damaging tumour cells. It has been suggested by a number of scientists that viruses may be the sole agents which transform normal cells into tumour cells. Howerer, since viral particles (virions) are rarely found in tumour tissues, it is more likely that the mechanism of transformation operates after viral infection by the in- corporation of the viral genome into the cellular genome. Normally this viral genome is repressed and unable to exhibit its presence. Agents such as X-rays, radiation, other viruses, and chemical carcinogens could partially derepress these viral genomes, forcing the manufacture of a number of new proteins in the cell. It is hypothesised that some of these new proteins are the active agents causing transformation into tumour cells. This hypothesis is consistent with the theory of Huebner (20). If we now take the evidence of Reslova, obtained from bacterial cells, and apply it to the mammalian cells, we can suggest that the primary lesions in the DNA caused by the platinum complexes act to derepress completely the viral genome. This then leads to the active multiplication of the viral particles, which may or may not be defective. I n any case this will almost certainly increase the antigenicity of the cell, and therefore stimulate the immune system to produce retaliatory antibodies to the tumour cells at an enhanced rate. It is also possible that, if the viral genome and the viral particles can be eliminated from the cell without concommitant cell death, the cell should revert back to its normal status. Such effects have been known to occur in the past. This speculation suggests a number of possible tests, and these are under way in a number of laboratories.

Future Outlook One platinum complex, the cis-dichloro-

diammineplatinum(I1) is currently on test at the National Cancer Institute in preclinical

trials. I t is anticipated that i t will be tested on human patients some time in the spring of 1971. It will be many months before sufficient clinical data will be available to allow a judgment of the efficacy of this new compound, either alone or in combinational drug therapy, in human tumours.

In the meantime, research must be pursued to develop analogues of the original compounds, and to continue testing these analogues on screening tumour systems. Without hesitancy I suggest it is now appropriate for inorganic chemists to join their organic brothers in submitting samples of their syntheses to appropriate Cancer Institutes for screening for anti-tumour activities. In addition to this chemical synthesis activity, it is desirable to know in more detail, and with greater security, the mechanisms of action of this new class of drugs, as well as their general toxicological and pharmacological properties in mammalian systems.

‘This class of complexes of the platinum group metals form a promising new class of drugs to be added to the medical armamen- tarium.

References I B. Rosenberg, L. VaiiCamp and 7’. Krigas,

Nature, 1965, 205, 698 2 €3. Rosenberg, E. Renshaw, L. VanCamp, J.

Hartwick and J. Drobnik, J . Bact., 1967, 93,

3 B. Rosenberg, L. VanCamp, E. Grimley and A. J. Thomson,Q. Biol. Chem., 1967,242, 1347

4 K. J. Bromfield, R. H. Dainty, R. D. Gillard and 13. T. Heaton, Narure, 2969, 223, 735

5 G. R. Gale, J. A. Howlc and A. B. Smith, Arch. Int. Pharmacodyn., 1971, in press

6 S. Reslova, International Symposium “Bacterial, Viral and Anti-Tumour Activities of Platinurn Compounds”, Mich. State Univ., Sept. 1970

7 B. Rosenberg, I,. VanCamp, J. B. Trosko and V. H. Mansour, Nature, 1969, 222, 385

8 €3. Rosenberg and I,. VanCamp, Cancer Res., 197% 3% I799

9 L. VanCamp, 1970, personal communication 10 R. J. Koeiba, S . D. Sleight and R. Rosenberg,

Cancer Cheniother. Rep., 1970, 54, 325 XI 1’. A. Connors and A. Haddow, International

Symposium “Bacterial, Viral and Anti- Tumour Activities of Platinum Compounds”, Mich. State Univ., Sept. I970

716

12 C. Welsch, ibid.


13 R. Him, ibid. I4 J. Vcnditti, ibtd. 15 J. ’Toth-Allen and B. Rosenberg, 1971,

16 11. C:. IIarder and R. Rosenberg, Z n t . J .

17 J. A. Ihwle and G. R. Gale, Bioclicm.

18 J. Drobnik, 1970, personal communication 19 J. Drobnik, A. Krekulova and A. Kubelkova,

20 K. J. Huebner and G. J. ’I’odaro, Proc. Natl.

submitted for publication

Cancer, 1970, 6, 207

l’hurinacol., 1971, in press

submitted for publication, 1971

Acud. Scz. US., 1969, 64, 1087

GLOSSARY Alkylating agent. A reactive chemical which replaces a hydroxylic hydrogen atom by an alkyl group. Bifunctional alkylating agents have two attachment sites (e.g., nitrogen mustard); mono- functional alkylating agents have one available attachment site (e.g., methylmethanesulphonate) Antibodies. Protein components (gamma globulins) of an immune organism which attach, with great specificity, to antigens and incapacitate them. Antigen (antigenicity). Any substance (usually proteinaceous) which when injected into an organism causes the formation of antibodies. Bacteriocide. Chemical agents which kill bacteria, usually important only if they produce tolerable effects in the host organism. Bacteriophages. A class of viruses which attack bacteria only. Carcinogen. Any agent (chemical, physical, bacterial or viral) which can produce a cancer in an organism. Carcinoma. A specific form of cancer which is a malignant tumour of lining cells and glands in the body of an organism. Carcinosarcoma. A mixed tumour with charac- teristics of both a carcinoma and sarcoina (see below). “Cure”. A complete disappearance of all detectable symptoms of a cancer for a minimal period of time (in humans, it is usually about five years). The double quote marks usually imply that the results are reported before this minimal time has elapsed. Cytotoxic. Refers to cell destruction or damage, usually caused by agents deleterious to any essential process of the cell. Cytoxan. Commercial name for cyclophos- phamidc, a very potent anti-tumour agent of the bifunctional alkylating agent class. DNA. Deoxyribonuclcic acid. A very long chain polymer consisting of alternating phosphate and sugar groups with attached purine and pyrimidine bases. The genetic information of the cell is coded in the sequence of these bases. Escherichia Coli (E. coli). A bacterium found in normal intestines. It is probably the most intensivcly studied organism in biology. Genome. The total genetic information of a cell. Interstrand Crosslinks. A chemical (covalent) link between two bases, each situated on one of the

two strands of double stranded nucleic acid (DNA, RNA). I t is generally believed that this link prevents the separation of the two strands which is necessary for genetic replication. Intrastrand purine dimer. A chemical bond (covalent) formed between two adjacent purine bases (adenine or guanine) attached to the same strand of a nucleic acid molecule. In Vitro. Refers generally to experiments done in a cell-free system. Here, however, it also encompasses the growth of mammalian cells in dishes. In Vipo. Refers to experiments done in an intact organism. LD,,. The dose, given under specified conditions, of any agent, which causes death in 50 per cent of the organisms. Leukaemia. A mass of relatively undifferentiated cells in uncontrolled growth, disseminated in the blood system. Specifically a disease of the blood and blood forming organs characterised by a permanent increase in the number of white blood cells. Lysis (Lytic). The bursting of a cell caused by the destruction of the cell membrane. Lysogcnic bacteria. Bacteria that contain the genetic information (genome) of a bacteriophage incorporated in the cellular genome. Melanoma. A tumour containing melanin, the black, polymeric pigment normally made in special skin cells. Purines. Aromatic, nitrogen-containing, ring moleculcs (adenine and guanine) with basic properties. One of the two classes of bases defining the genetic code by their sequences in nucleic acids. Pyrimidines. Cytosine and thymine. The second class of aromatic, nitrogen-containing ring structures, that occur in nucleic acids, and define the genetic code. Repression (derepression). The forcing of a gene into an inactive state. A repressor molecule, believed to be a protein, blocks substances which turn genes on, or interferes with the genes’ ability to eventually produce a specific protein. RNA. Ribonucleic acid. A long chain polymer consisting of alternating phosphate and sugar groups with attached purine and pyrimidine bases. May be the sole source of genetic information in the organism, and additionally acts as an intermediary to transfer the genetic code into specific protein manuf. xture. Rous Sarcoma Virus. An RNA containing virus which is the causative agent of tumours in fowl. Sarcoma (S-180). A specific form of cancer which is a malignant tumour of supporting tissue in the body of an organism. Virus (Virion) Defective-Active. Infectious disease-causing agents which are smaller than bacteria and which always require an intact host cell for replication. They may contain either DNA or RNA as the genetic material. The nucleic acids may be double stranded or single stranded. Defective viruses are incapable of infecting host cells, or cannot replicate once their genome has invaded the cell.


Surface Phenomena on Rhodium-Platinum Gauzes CATALYST ACTIVITY DURING AMMONIA OXIDATION

By J. E. Philpott Johnson Matthey Metals Limited

The rare occurrence of inactive catalyst gauzes for no obvious reason has led to comparative studies of the structures of rhodium-platinum wires from both active and inactive gauzes. Active gauzes showed the regular development of octagonal crystal faces on the nodular growths on the wires. Inactive gauzes showed no crystal development and an amorphous growth appeared on the wires. Segregation of rhodium and iron at the surface occurred in this case, perhaps due to unusual plant operating conditions, and may have caused deactivation.

The use of rhodium-platinum alloy gauze as the catalyst in the modern process for ammonia oxidation is well established, as shown by the large number of papers reviewed previously in this journal ( I ) and elsewhere (2). At the present time there are in the world more than 450 nitric acid plants and almost without exception they use platinum alloy catalyst gauzes, usually of 10 per cent rhodium-platinum.

The oxidation process is highly efficient and over a wide range of operating conditions a nearly quantitative conversion of ammonia to nitric oxide can be obtained. Conversion efficiencies of between 92 and 96 per cent are commonplace and are consistently achieved throughout the lifetime of a plant. In general the shortfall from maximum efficiency is probably due to some decomposition of the ammonia feedstock before it reaches the gauzes, rather than to significant yields from possible alternative reactions ( I , 2) that can take place on the gauzes.

On rare occasions, however, a case is found of a catalyst gauze pad that is inactive. Although apparently indistinguishable from other gauzc pads, the inactive gauze pad does not maintain its initial conversion efficiency

and uneconomical yields are obtained only a short time after igniting the pad. It would appear that the high selectivity of the catalyst gauzes for promoting the desired oxidation reaction steadily declines and that yields from alternative side reactions become significant. Treating the inactive gauzes with constant boiling hydrochloric acid and replacing them in the plant does not improve their performance. Replacement of the inactive pad by a fresh pad of gauzes has always overcome the problem but has done nothing to explain it.

Analytical examinations of inactive gauzes and of the material from which they were woven and cut do not give any indication of the cause of inactivity. The chemical composition of the gauze material has always been found to lie within the tolerance limits. Analysis to determine whether some unusual impurity had been sealed into the wire surface during the wire drawing process, or whether the retention by the gauzes of impurities entrained in the feedstock gas might account for the drop in activity, did not reveal any cause of the inactivity.

Although inactive gauze pads occur in- frequently and are more of an occasional


Fig. 1 Carcful inspa tLon of gauzes fabricated by .Johnson Matthey Metals before dispatrh to nitric nccd plants. Y’he fiat rircuEar pattze mil2 be Enstalled in a mediuin pressure plant and the smaller hemgonal games zn high pressure plants. The largi, rolled czrcular g:cizcze loill be installed En a plant operating at atmospheric presnuro

embarrassment than a constant cause of trouble, a niore detailed examination of them was undertaken as part of a research pro- gramme to study the fundamental mechanisms involved in ammonia oxidation for nitric acid production.

Examination of Inactive Ganzes ’To this end a number of inactive gauzes

from two medium pressure plants were examined at various periods in their lifetime and the results, together with the results from a more general examination made of spcnt gauze pads taken from all types of plant in various parts of the world, were compared with those obtained from an examination of several inactive gauzes from two inactive gauze pads. A description of the results follows with a series of scanning electron microscope and electron microprobe analyser photographs illustrating the state of the gauze surface at various stages.

Platinum Metals Rev., 1 9 7 1 , 15, (2)

It has been previously reported (3) that rhodium-platinum gauzes develop nodules or “brussels sprout” growths on their surfaces while in operation in nitric acid plants. The catalytic activity of the gauzes appears to be related to the development of this nodular growth, since fresh gauzes with smooth as- drawn wire surfaces are inactive and need to be activated before they will oxidise ammonia efficiently. For this reason replacement gauzes are usually installed beneath some of the older activated gauzes already in the catalyst pad. When a new pad is being commissioned, each gauze in the new pad is activated by playing a hydrogen flame over its surface until the gauze just glows red. Alternatively, a few activated gauzes obtained from a plant already in commission are inserted on top of the fresh gauze pad and serve to ignite the remainder.

The photograph in Fig. 2 shows a gauze of 0.003 inch diameter wire with the wire in

53

F‘ig. 2 l O P ( , Rh-l’t gauze ioire 0.003 inch diameter i n the as-drawn condition showing the uniforni grain structure and absence of nodules on the wires

k’ig. 3 The gauze of Fig. 2 after half the normal gauze life installed in a nitric acid plant showing the nodular pattern typicctl of an active gauze

l+‘ig. 4 A n eizlarged a ieu of the crossoz’er point of two gauze wires .from the gaua:! i n Fig. 3 showing the octagonal crystal structure and the nodules. iohich are concmtmted on the wire surfaces between crossover points

installed in a nitric acid plant for half the normal gauze life period. Its surface shows the development of the nodular pattern typical of an active gauze. An enlarged view of the crossover point of two gauze wires from the same gauze is seen in Fig. 4. A clearly developed octagonal crystal structure can be seen in the enlargement and also the development of the nodules, which appear to be concentrated on the surfaces between the crossover points. Perhaps nodular growth at crossover points is inhibited by the slight movement of the wires that occurs while the gauze is in service. The structure seen here is generally typical of active gauzes whether they have been operated in low, medium or high pressure plants.

When individual gauzes from an inactive pad are examined, a markedly different structure is observed. The regular development of octagonal crystal faces cannot be distinguished and an amorphous “cauli- flower”-like growth as illustrated in Figs. 5 and 6 is seen, in contrast to the “brussels sprout” nodules usual on active gauzes.

Segregation at Wire Surfaces The obvious visual difference in these

highly magnified photographs suggested that electron image determinations might produce interesting results. Accordingly, two sets of

the as-drawn condition. The uniform grain active and inactive gauzes were examined, structure and absence of nodules on the each set taken from one of two different individual wires can easily be seen. Fig. 3 medium pressure plants many thousands of shows the same gauze after it has been miles apart. The electron image photographs


Fig. 5 AII inactive puuze after a f h (lays installed in a nitric m i d plant showing the rrbsence of octcrgonul crystal ,faces

Vig. 6 An, edarged v i w of the g a m e toire shown in Fig. 5 with the cnullflozuer-lilce amorphous ,growth clmrcrcteristic of innetiiie gauzes

of both sets of gauzes were similar and those taken from one set are shown.

Examination of the electron images from the active gauzes (Fig. 7) shows that the wires were homogeneous and no unusual features are visible. In the electron images of the inactive gauzes (Fig. 8) a clearly defined concentration of material is seen on the surface of the wires. This segregation on the

Fig. 7 (right) Electron and X-ray images of spent active gauze showing its homogeneity. n ( top) l

Fig. 0 l+:lrrtron and X-rmy images of spent inactiiie gauze showing srgrrgation of material at the surjacr ( I

6 l’t M E X - r a y image Elrctron image of cross-sertion of gauze

r Hh I,a X - r a y image Y 360

the effect is really due to the micro-section being a plane through the middle of the gauze so that more of the wire surfaces is visible at the crossover points where the wires dip and rise in crossing each other.

The composition of the material shown in Fig. 8c is very probably rhodium present as rhodium oxide Rh,OB. A similar electron image was seen showing a concentration of iron, probably as FerOa, which was associated with the surface concentration of rhodium. Neither of the active gauzes examined showed any sign of surface concentration of rhodium or iron oxides.

On both sets of inactive gauzes the cauli- flower-like nodular structure and the concentration of rhodium and iron oxides on the wire surfaces were found to be present on all the gauzes in the pad although they became less severe from the top gauze downwards.

Surface concentrations of rhodium and iron have not been found on material from which the gauzes are cut out so it is thought that they develop within the plant itself. The factor or factors which initiate the con- centrating process may be connected with some flaw in the manufacturing procedure but, since reports of inactive gauzes are related to individual ammonia burners rather than to batches of woven material from individual suppliers, it seems more likely that these factors will be found to lie in some unusual operating condition in the plant itself. A possible cause is a prolonged period of operation at low temperature, thereby en- couraging the slow separation and concentration of rhodium oxide on the surface together with the preferential retention of small particles of iron oxide from the fecd- stock on the rhodium oxide, whereas at

wire surface appears to be more marked at temperatures above 900°C rhodium oxide the crossover points but this is not so because would be expected to volatilise.


Fig. 9 ( ;awe fabrication vn tl7e looms in the .Johnson Matthey Metals g a i m shop. i~h f ) f~ ium-pl f l t in iLn~ gauzes 7 ~ p to 140 in (3.56 metres) wide (ire wot~eri f r o m 0.003 in diamrtw w i r e

‘The development of these inactive surfaces is the subject of further research work and in a later article it is hoped that an explanation will be given of the fundamental causes that lie behind these observations.

Acknowledgements References The author is much indebted to Dr G. J. I

Platinum Metals Electrodeposited from Molten Cyanides By D. Schlain, F. X. McCawley and G. R. Smith US. Dept. of the Interior, Bureau of Mines, College Park, Maryland

While conducting research here at the Metallurgy Research Center on thc electrodeposition of platinum group metals from molten cyanide baths we have prepared platinum metal objects by electroplating or electroforming. The electrodeposition of platinum group metals on various substrates from molten cyanide baths was described by Rhoda ( I ) . We have described our modified methods to electrodeposit thick protective coatings of platinum, iridium (2), palladium (3), and rhodium (4) from molten cyanides.

Three crucibles were electroformed. One is of iridium, one inch inside diameter and $ inch deep with a 5 mil wall. The second crucible is formed of platinum, 2 inch inside diameter and one inch deep with a 5 mil wall. The third, also of platinum, is electroformed with a thermocouple well for differen- tial thermal analysis work, inch inside diameter, 2 inch deep with a 15 mil wall.

Crucible tongs were coated with platinum, 2.5 mil thick on the arms and 5 mil thick on the tips. In addition, such items as thermocouples, a nickel-chromium-iron rod used

, I I hree c:rucibles urtd two pairs of crucilrles tongs fdwictited und coated with plat inum metals. T h e largcst crurible was electrofornied of iridium, the others of plat inum. The tongs it1er~ couted with plntinum. Wall and coating thicknesses range ,from 2.5 mil to 15 mil .


as a seed holder in a molten calcium germa- nate bath, and 8 copper thermal E.M.F. probe have been heavily coated with platinum or iridium for corrosion resistance. Objects were electroformed of platinum or iridium using suitable mandrel metals.

A molten cyanide process has also been developed for treating substrates before plating with platinum group metals in aqueous baths (5 , 6).

References I R. N. Rhoda, Plating, 1962, 49, (I), 69-71 2 R. I,. Andrews, C. 13. Kenahan and D. Schlain,

U.S. Bur. Mines Rept . Invest. 7023, 1967 3 R. L. Andrews, G. R. Smith, C. B. Kenahan

and D. Schlain, U.S. Patent 3,5 17,789 4 G. R. Smith, C. B. Kenahan, R. L. Andrews

and D. Schlain, Pluting, 1969, 56, (7), 805-808 5 S. I). Cramer and D. Schlain, Ibid., (s),

5 16-522 6 S. D. Cramcr, C. €3. Kenahan and D. Schlain,

U.S. Patent 3,3og,2g-o

Pressure and Thermal E.M.F.s TEE EFFECT ON RHODIUM-PLATINUM THERMOCOUPLES 1 A thermal e.m.f. is not only a function of temperature, it is also affected by pressure, a fact that is not as widely known. T o the geophysicist studying chemical and physical behaviour at pressures of several thousand atmospheres correction for the effect of pressure is essential.

In a recently published paper I. C. Getting and G. C. Kennedy (I) describe a technique for determining corrections on single thermo- elements where, under thermally symmetrical conditions, one-half of a homogeneous wire is pressurised while the other half is main- tained at atmospheric pressure. This is a method previously used by Wagner (2), Hridgman (3) and Bundy (4) among others.

Getting and Kennedy's apparatus con- sisted of a piston-cylinder device with talc as a solid pressure medium. The thermocouple wire was fed through a tube at atmospheric pressure to the thermal centre of the furnace where it entered the cell through a pressure seal. Inside the cell the wire was coated with binderless boron nitride to preserve electrical insulation yet ensure uniform pressure transmission. The temperature of both seals was recorded so that the temperature gradient along which the pressure was applied could be calculated. The cell was heated internally by a co-axial graphite heater.

A number of excursions were made into the pressure-temperature field ranging up to a maximum of 1o0o"C and 35 kbars. The thermocouples selected were Chromel : Alumel and platinum: 10 per cent rhodium-platinum since these are two of the most commonly used combinations. These thermocouples have previously been the subject of investigation by Bell et al. ( 5 ) , and Hanneman and Strong (6) among others.

Extrapolation of the results obtained shows that Chromel: Alumel may read as much as z8'C high at IZOO'C and 50 kbars while platinum : 10 per cent rhodium-platinum reads low by a similar amount at zooo"C and 50 kbars.

The authors acknowledge that pressure is only one of several factors affecting the e.m.f. generated by a thermocouple and observe that chemical contamination is a particularly difficult problem. Unfortunately their paper does not indicate whether any steps were taken to measure the degree of contamination and if so how their results were adjusted to allow for this factor. Curiously they also omit an expIanation of the value of extrapolating to 2000 C when the platinum limb of a thermocouple normally melts at 1772'c. The reader is left to infer that pressure raises the melting point sufficiently to make this a meaningful exercise.

These criticisms apart the results should prove to be valuable to workers in this experimentally exacting field of research where reliable data on e.m.f. correction are still very scarce.

P. H. W.

References I I.

The Platinum Metals in Organic Syntheses ORGANOMETALLIC COMPLEXES AS PREPARATIVE REAGENTS

By B. F. G. Johnson University Chemical Laboratory, Cambridge

r , 1 hc. synthesis of organic molecules is of growing importance to the chemical industry but conz1entional methods are becoming increasingly inadequate. 'I'ransition metal complexes, i n par - ticular those of the platinum nzeiuls, provid(> routes in s.vnthetic chemistry to many usefil and interesting compounds. TIrre the principles involved are explained and (I . number of the reactions ore dtwrihetl.

It is now apparent that the application of transition-metal organometallic compounds to the synthesis of organic molecules is one of the most powerful preparative tools available to the chemist. This article is an attempt to present some of the current ideas concerning the structure and reactivity of such organometallic complexes of the platinum metals and to apply them to the preparation of organics.

To date much of the emphasis has been placed on complexes of iron and consequently some of the principles are explained by reference to that metal but there is growing interest in the platinum metals, which havc already proved their versatility in so many fields of chemistry. In no way is this a rigorous and complete exposition but it is hoped that an introduction to these ideas will serve to indicate the synthetic potential of reactions involving organometallic rcagents.

Coordination In synthetic reactions involving metal ions,

activation of simple molecules such as H,,

CO, olefins, acetylenes, aromatic species and many other compounds takes place through coordination. This act of coordination has a number of effects.


Change in Reactivity The act of coordination alters the electron

distribution within the organo group. This very often involves donation of electron density (z) from the organic molecule (e.g., as with olefins) to the metal so that electron distribution within the molecule can be extensive. When coordinated to Pd(II), for example, an olefin, normally susceptible to electrophilic attack, now reacts with nucleophiles.

I

modification in behaviour or change in metal. The bonding of olefins to metal ions is

generally considered in terms of the Chatt- Dewar-Duncanson Model. This simply views the bonding as being composed of two parts :

(u) the donation of electron density f rom the filled ethylene z-orbitals into an appropriate metal 0-orbital, e.g. dspz in the case of four coordinatc platinum(I1) having a square planar configuration.

i Pt 5 P 2

i C

(h ) back donation from the filled d-orbitals of the transition metal (e.g. dxz with I’t(I1)) into the empty anti-bonding orbitals of the olefin.

TT ant i bond I n y .-. _. o r b i t a l

I I i’t

For such a metal the metal-olefin bond

(i) The metal, its electronic configuration

(ii) the auxiliary ligands present; and (iii) the olefin itself. Consider, for example, Zeise’s salt, an

ethylene complex of platinum(I1). Since the metal is in a relatively high oxidation state a drift of electron density away from the ethylene to the metal via the o-bond ((a) above) would be expected. For the same reason little drift of electron density back to the olefin via the x-bond is expected to occur. Consequently the ethylene acquires a net 8 character and undergoes nucleophilic addition reactions.

obviously depends upon :

and oxidation state;

I / ’ 6+ c - .

In contrast for olefin complexes of Fe(O), Ru(O), or Os(O), e.g. C,H,M(CO), (M Fe, Ku or Os), since the metal in this situation has a large degree of electron density associated with it, o-bond formation is poor, whereas back donation would be expected to be good with the formation of a strong ;7-bond. In this case, the net result is electron density build-up on the olefin leading to susceptibility to electrophilic attack.


The role of auxiliary ligands or groups is also understandable under these terms. Highly clectronegative ligands result in electron drift away from the metal and this is re- flected in the enhancement of the activation of the olefin towards nucleophiles, whereas highly electronegative substituents on the olefin (e.g. CF, groups) would cause an even greater electron movement from the metal to the olefin. Many of the reactions of metal-olefin complexes may be rationalised in these simple terms. Other factors, of course, must also be considered. Often, for example, auxiliary ligands produce strong steric effects which cause modification of the reaction path.

Stabilisation of “Unstable” Organic Moleeules

Perhaps one of the most dramatic aspects of this field is the stabilisation of organic molecules which do not exist in the free state. Beyond question the most notable example of this type of behaviour is cyclobutadieneiron(tricarbony1). Cyclobutadiene has excited organic and theoretical chemists

alike for many years but prior to the work of Pettit and his co-workers no good evidence for the existence of this molecule was available. Cyclobutadieneiron- (tricarbonyl) shows many of the properties associated with aromatic systems. Thus the ring system readily undergoes electrophilic reactions (see scheme on right).

An important facet of this work is the ease with which the free organic is produced on oxidation with Ce(IV), for instance liberation of cyclobutadiene in the presence of a dienophile leads to the production of Dewar benzene derivatives. This is important since if such reactions are to have any potential synthetic use then it must be possible to remove the metal under conditions which are not too violent, such that the organic group is not decomposed.

Stabilisation of Unusual Conformers or Tautomeric Forms

Very often the organic molecule under consideration can exist in a number of con- formations or tautomeric forms. In such cases, because of the stereochemical require- ments of the metal ion, the organic group may be “forced” to adopt a particular arrangement. For phenol, for example, two tautomeric forms may be written.

Another example is provided by cyclooctatetraene which coordinates to a variety of metal ions including Fe(O), Rh(1) and Pd(I1). The conformation adopted on coordination depends entirely on the metal ions employed even though all have the same (d*) electronic configuration. Thus with Rh(1) and Pd(I1) the tub conformation is preferred whereas with Fe(0) a chair form is observed (in the solid state). (See Figs. 1-111).

!a) (b) Fe (CO),

In the free state only tautomer (a) is observed.

shown here (right), it is possible to isolate an iron- (tricarbonyl) derivative in which the ketonic form ( b ) is stabilised.

By the reaction sequence 0


It is relevant to note that a further form of CHH, has been noted for osmium complex CHH,Os(CO), (See Fig. IV).

ordination simply redirects the course of this attack. Here the M(CO):, unit may be regarded as a protecting group.

Some Reactions Described Formation of Carbon-Carbon Bonds

Olefins readily undergo nucleophilic addition in the presence of Pd(I1) or Pt(I1) salts. The reactions of many nucleophiles have been examined but possibly those of greatest interest to us are those involving

dichloride or (cycloocta-1,s-diene)platinum dichloride with the conjugate bases of malonic

group (albeit on coordination) Reaction of (cycloocta-1,s-diene)palladium (see below).

Reduction of the Reaction Course esters, keto-esters, or p-diketones leads to

It is then possible to examine the reactivity of such usual modifications of the organa-

carbanions. By such reactions carbon- bond formation is possible*

Finally it is important that we realise the behaviour of organic groups coordinated to metal ions can be modified in rather subtle ways. Cyclooctatetracne does not undergo any of the typical aromatic reactions under the usual “organic” conditions. For example, = Pd or Pt under Friedel Crafts conditions, rather than acetylation, polymerisation occurs with only minute yields of the expected acetyl derivative. In fact the majority of the chemistry of cyclooctatetraene is concerned with such polyrneri- sations. However, recently it has been shown that on coordination to a Fe(CO), or Ru(CO), unit the reactivity of cyclooctatetraene is modified sufficiently to allow acetylation, formylation and other electrophilic reactions to occur

e M CI,

\

complexes (1~2) which contain a new carbon- carbon bond; e.g.

CH!C02R)2

CH(COM4,

The complexes (1~2) have IS and z bonds with the metal and in certain cases undergo further transformations on treatment with base, the course of the transformation depending very much on the strength of the base employed. Treatment of (IU) with a strong

readily. One could consider this modification in reactivity to be subtle in the sense that the molecule is susceptible to electro-

I CH(CO,R),

(5)

philic attack both in the free and coordinating state but that the act of co-

(3)


modified

base produces a bicyclo [6, I , 01 nonene derivative (3) and palladium metal. Another moleculc of malonate gives rise to a compli- cated reaction sequence. Attack occurs intermolecularly at the x-complexed olefinic bond and is followed by a transannular reaction of the eight membered ring to form a bicyclo [3, 3, 01 octane ring system containing two malonate groups (4). I n contrast, if attack of a second carbanion is encouraged by reaction with tertiary phosphine as with complex (2) a cyclooctene is the product when M Pd, but a chelating a-bonded cyclooctane when M Pt (6):

Carbon-carbon bond formation is not restricted to thc nucleophilic addition of carbanions to co-ordinated double bonds. It is also possible by oxidative coupling of olefinic and aromatic compounds in the presence of, for example, palladium(I1) acetate.

Pd(0Ac) ArCH CH, ArH ,Ar Pd ( = ) / N a o % H O A c C J g g ladium acetylacetonate (7) to give allylacetone .I (8) via ligand coupling.

Other coupling reactions find their uses :


Whereas carbon-carbon bond formation of several important industrial processes. By takes place by nucleophilic addition to this means many useful and important CO- olefins coordinated to palladium or platinum containing organics may be produced. Most entities, on coordination to iron, ruthenium important is the carbonylation of ethylene, or osmium tricarbonyls it rakes place by e.g. electrophilic addition. I n general this is not CH, CH, of particular synthetic utility since olefins themselves undergo such reactions. However, CE-I, CH, in particular cases, it is of tremendous importance. One case, that of cyclobutadiene, has been described above in some detail. Other important examples are the cyclo-

CH, CH,

co co

CICH,CH,COCl : Pd

PdCl, , ROH CH,CH,CO,R 1

CH,CH,COCH,CH,CO ;R

CH,CH,CHO C,H, l’dC1; i H, ->

octatetraene and cycloheptatriene complexes Such reactions have been studied extensively of iron or ruthenium tricarbonyl. Both and are, of course, catalytic. However, car-

bonylation of more “exotic” organics pro-

vides a useful route to many interesting organics polymerise under normal electro- cyclic systems, e.g. (9) and (10) philic conditions but, on coordination, Carbonylation of z-allylic derivatives pro- addition reactions take place efficiently, vides a direct route to unsaturated acids,

acid chlorides and esters:

CH, = C HC H,CO,R t Pd + HCI

The carbonylation of acetylenes also allowing a complete systematic chemistry provides routes into useful organic molecules. to be built up. Numerous transition metal complexes are

known to be active for cyclisation or oligo- Carbonylation and Decarbonylation merisation of acetylenic compounds. Of

The carbonylation of olefins in the presence particular use is the employment of transition of transition metal catalysts forms the basis metal units to produce cyclic ketones. Here


the carbonyls of Fe, Ru or 0 s and various Pd derivatives are of particular note.

Ph

WP - (JO Ph C E CPh + CO

Systems containing N may also be carbonylated by these methods.

Large Ring Chemistry It is often of considerable use to be able

to carry out specific substitution reactions on ring systems. Here metal complexes can be extremely useful. Con-

or platinum undergo nucleophilic addition to give complexes of the type:

sider the chemistry of coordinated [;)-ptA" - 50- - C_yq 1,s-cyclooctadiene. Complexes of this 'CI compound may be formed with Fe(O), Ru(O), Os(O), Rh(I), Ir(I), Pd(I1) or Pt(I1). As discussed above (commencing on page 63) for the formation of carbon- carbon bonds, the complexes of palladium

In contrast, the analogous complexes of Rh(I), Ir(I), Fe(O), Ru(0) or Os(O), do not undergo such additions but rather electrophilic reactions of the type:


R

In fact for M Fe, form I11 is observed; for M - Ru, form I1 and for M - Os, a mix- ture of I1 and 111.

form 11. Thus on simply changing from M Fe to M - Ru or 0 s different tautomeric forms of CsH8' may be

to produce allylic derivatives by H abstrac- stabilised and their chemistry examined. tion. These salts then undergo subsequent Thus on reaction with nucleophilic reagents nucleophilic addition to give derivatives in neutral bicyclic or monocyclic derivatives are which an alternative type of substitution was obtained: obtained as shown above.

Earlier we noted the - - 1 o R u ( C O & 1 -+ + I?@- RU(CO), ability of metal containing units to stabilise organic L - J molecules in unusual con-

firmations or tautomeric forms. This enjoys wide R = (0.g 1 CN - synthetic application and here we will consider the cyclooctatetraene complexes, CxH,M(CO):,, of iron, ruthenium and osmium. All three are readily protonated by strong acids such as HHF,, HPFo or

ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES Vapour Pressure and Ireat of Sublimation of Platinum B. R . FLANTE, A. R. SESSOMS and K. n. PITCH, J . Res. X B S , Pt. A, Pliys. Cheni., 1970, 74A, (5), 647-653 The vapour pressure of Pt was measured by the Langmuir method at 17oo-zoooK and the results are tabulated. The mean value of the third law heat of sublimation is 564.49.; 2.1 kJ,'mol, but second law values tended to be lower due to experimental error.

Photoelectric Iletermination of the Work Function of Gold-Platinum Alloys K. ~ O U W M A N and w. 11. M. SACHTLER, J. Catalysis,

Films of Pt, Au and their alloys were prepared by vapour deposition. The photoelectric emission of these films was investigated. Equilibrated alloys of compositions within the miscibility gap of the Pt-Au phase diagram possessed identical work functions. This result agrees with the expectation that the Au-rich alloy envelops crystallites of the coexisting Pt-rich alloy. CO causes an enrichment of the Pt in rhe surface.

Orderiug in Fe-Pt Alloys E. N. VLASOVA and T. P. SAFOLIIKOVA, Fiz. Metal. Metalloved., 1970, 30, (s), 980-985 X-ray studies of the ordering of monocrystalline 32 at.'):, Pt-Fe during isothermal annealing at 750 C indicated initial formation of a metastable homogeneous structure succeeded by separation into two ordered phases FePt and Fe,Pt.

1970, 19, (2 ) , 127-140

IZesistive Hehaviour of Dilute PdFe Alloys about the Curie Temperature

I'hys. Rev. B., 1970, 2, (6), 1587-1592 The behaviour of the magnetic part of the electrical resistivity pm of 0.1-1.0 at.;!, Fe-Pd near the Curie temperature was analysed. The ferromagnetic critical temperature was determined from the location of the maximum in dp,.'dT, and varies with concentration as Cn, where 11 1.65 : 0.05.

Thermodynamic Properties of Solid Nickel- Platinum Alloys K. A. WALKBK and J. B. DARRY, Acta Metall., 1970, 18, (12), 1261-1266 'The activities and free energies of solid Ni-Pt

M. P. KAWATKA, J. I . RUDNICK and J. A. MYDOSII,

alloys at 1625 K were calculated from vapour- pressure measurements. Heats of formation at 298 K were measured by liquid Sn solution calorimetry. The results reflect the ordered structures that exist at low temperatures in the h'i-Pt system.

Magnetic Investigations of the Isoelectronir Palladium-Platinum System

5-8 The magnetic susceptibility of Pd-Pt was measured at 14-800 K, and shows a sharp increase with increasing Pt concentration. New electronic band and density of states calculations are presented, and x(O,c) results for the Pd-Pt system are discussed in terms of these and the Stoner-Wohlfarth enhancement formula.

W. THEUTMAN, %. Angew. PhyS., 1970, 30, (I),

Thermal Stability and Structure of the 7"; Rh-Pt Alloy in Relation to Prior Defor- mation E. I . RYTVIS and L. A. MLDOVYI, Metalloved. Term. Obrabot. Metal., 1970, (I I ) , 53-55 The amount of deformation of an annealed 7(;,> Rh-Pt alloy affects its structure and the rate of creep. At 1400 C the minimum resistance to creep corresponds to IS":, deformation; at 1200 C to 8?, deformation.

Electrical and Tensile Properties of Cu-Tho,, Au-ThO,, Pt-ThO, and Au-Al,O,, Pt-A41,0, N. FUSCIIILLO and M . L. GIMPL, -7. Mater. S'ci., 1970, 5, (12), 1078-1086 Dispersion-strengthened alloys of Pt, Au and Cu containing l h O , and Al,O, were prepared by precipitating the elements from a solution containing a suspension o f the oxide phase. Alloys containing C : Z vol.%, oxide phase could be made into wire. Tensile strength, elongation, hardness and resistivity were measured as a function of temperature up to IOOOT. The alloys exhibit high conductivity and superior strength, hardness and oxidation resistance at high temperatures.

Thermal Expansion of Khodium, Iridium and Palladium at Low Temperatures G. K. WHITE and A. T. FAWLOWICL, J . Loeo Temp.

Coefficients ( x ) of linear thermal expansion of Rh, I r and Pd are 8.45, 6.65 and 11.78 :: Io'/deg K at 283K and 3.50, 3.43 and 6.21 x ro6/deg K at 75K. At temperatures below IOK cc may be represented by

~'Jz.Ys.> 197% 2, (5-61, 631-639


I O ~ " C C - 20T ro.052'l'J (Rh) 1 0 ~ 0 % 9T o.070T3 (Ir) TO"'% 40.'j'I' 0.43'j?'3 (Pd)

The ?' and T3 terms are identifiable with electron and lattice vibrational components.

New Data Concerning the Migration of Hydrogen and 1)euterium 1)issolvcd in Palladium under the Action of an Electric Field A. 1iEROI.D and j.-ti. RAT, c. R., sir. c, 1970, The previously described migration of H, and D L dissolved in a I'd wire under the action of a continuous current cannot be reproduced in the presence of traces of hydrocarbons. The mobilities obtained from the flow of the transported gas are less than those calculated using thermal diffusion coefficients, which indicates an incomplete ionisation of the dissolved atoms.

271, (I3), 701-704

Note on the Debyc: Temperature of Palladium J . s. BROWN, J . Ph-yr. C, Solid State Phys., 1970, 3> (91, L,I75-L177 A comparison of the values of the Debye temperature for f.e.c. I'd is given for several different model calculations, and a correlation with various experimental results is discussed.

Study of the Diffusion of Hydrogen in Pd and I'd-Ag Alloys with a Pulse Method Ir. Z ~ C H N E R , %. Naturf. A , 1970, 25, (IO), 1490- I496 LXffusion coefficients of H, in Pd and I'd-Ag alloys were determined at low H, concentration and 0-60 C by an electrochcmical pulse method. 'l'he pre-exponential factor D, decreases slightly with rising Ag content. The energy of activation depends on the Ag content, going through a minimum at NN 15'2, Ag.

1. Study of the Adsorption of Hydrogen on Filanients of Purr Palladium €3. TARDY and s. J. TEICHNBK, J . Chim. Phys., 1970, 67, (11-12), 1962-1967 The adsorption of H, on evacuated Pd filaments was studied by flash desorption. The desorption curves are complex due to impurities (CO and H,O) which are also desorbed. Gas analysis shows adsorption of a single species of H, on Pd in an amount less than the value corres- ponding to a monolayer. 11. Adsorption of Hydrogen on a Series of Gold-Palladium Alloys Ibid., 1968-1972 The adsorption of H, on Au-Pd alloy filaments was studied. The amount of H, adsorbed increases with the Au content up to 30(%~, then decreases when the Au content is 50'2,. The latter value corresponds to complete filling of the d orbitals of Pd.

Investigation of the Pd-Ba Composition Diagram E . M. SAVITSKII, v. 1'. POLYAKOVA and E. M. KHORLIN, Izv. Akad. Nauk S.S.S.K., Metally,

Ihe composition diagram for up to 33 at.%, Ha-I'd alloys was constructed and showed that BaPd, and BaPd, are present.

Energy Bands in P'-PdIn s. J . CHO, I'hys. Statzts Solidi, 1970, 41, (I), 179-189 The energy bands for ordered P'-PdIn were calculated by the augmented plane wave method. The possible open orbits were studied, and the electronic density of states curve was obtained from the energy bands. Estimates of the electronic specific heat coefficient, the magnetic susceptibility, and the cyclotron effective masses are given. Results are compared with existing optical data.

Remarkable Interstitial IIydrogcn Contents Observed in Rhodium-Palladium Alloys at High Pressures

1970, (6), 143-145 ,.

T. €3. FLANAGAN, €3. BAKANOWSKII and S. MAJCHRZAK, .7. I'hw Chem., 1970, 74, (24, 4299-4300 A H:Pd atomic ratio greater than I was found in an alloy system, Rh-Pd, where the added metal is probably a nonabsorber of H,. At 2300-5100 atm stoichiometric I :I hydrides were obtained for the 20'2, and 30'%, Rh-Pd alloys. Either Rh can absorb H, but at a higher pressure than Pd, or Rh functions as a €1, absorber only when in the I'd matrix

The Thermodynamic Properties of Solid Palladium-rich Pd-Cd, Pd-In, Pd-Sn and

J. n. DAKBY, K . M. MYI.BS and J. N. PRATT, Acta Metall., I97X, 19, (I), 7-14 Vapour pressure measurements were used to calculate the activities and free energies of formation, at 1350 K, of Pd-rich Pd-Co alloys. Entropy of formation values were found by combining free energy results with heats of formation (AHf) at 298 K. AHf values were also found at 298 K for the =-phase I'd-rich alloys of the polyvalent solutes In, Sn, Sb and for the intermediate phases PdSb and PdSb2. Results suggest some correlation between the four alloy systems.

Thermoelectric Power of Palladium Based Dilute Alloys D. GAINON and J . SIERRO, Helv. Phys. Acta, 1970,

The thermopower, S, of I at.?, M-I'd (where M Ti, V, Cr, Mn, Fe, Co, Ru, Re, Os, Te) was measured at 1.5-273 K. For the ferromagnetic alloys a change of slope of S exists near the Curie temperature. Pd-Cr shows a large positive

Pd-Sb Alloys

43, (6-7), 541-554

Platinum Metals Rev., 19 7 1 , 15, (2) 69

value of S at low temperature, but for the other alloys S is both positive and greater than when the same dilute elements are dissolved in noble metals, but is not anomalously dependent on temperature.

Composition 1)iagram of the Ti-Ir System v. N. BKIWENKO and T. D. sIimrA, Izo. &ad.

Studies of the T - I r system indicated a stable CsC1-type phase in 30-40 at.';!;, Ir-Ti at high temperatures based on T - I r stabiliscd with extra Ti . No eutectoid decomposing to P-phase

~ v a u k S.S.S.R., Mctully, 1970, (6), 197-203

at 500"5c;(l solutions of Ru and Ta, explained by the formation of monoatomic films of Ru on the surface of the solid solution, and a work function

K. A. KRIBS and G. J. I.API'.YRI

plexes of Pt and Pd with PPh, and divalent benzonitrile, ethylene and amine complexes with Pd and Pt are described.

The Chemistry of Transition Metal Carbonyls. Synthesis and Reactivity I:. w. ABEI. and F. G. A. STOKE, Q. 12ev., 1970, 24, (41,4983'52 The preparation and properties of many transition metal carbonyls including those of the platinum group metals are described.

ELECTKOCHEMIS'JK Y ISlectrocatillytic Activity of Platinum-Ruth- eninni :Way Black for Mctlianol Oxidation M. WATANABI;, T. SUZUKI and s. MOTOO, Denki Kajiakzi, TWO, 38, (IZ), 92.7-932 'I'he dependence of the activity on the composition of l't-Ru alloys was investigated. Pt and Ru were alloyed with T i and developed in HI; solutions to give the black, which is a f.c.c. solid solution of Ru in 1% The catalytic activity increased sharply till the Ku:l't ratio was 2, then decreased sharply till the ratio was 3. It is proposed that the Pt atom requires 2-3 Ru atoms as its nearest neighhours for maximum clectrocatalytic activity.

Anion Adsorption on Palladium v. s. VII.INSKAYA, K. H. BUKSHTEIK and M. K. TARASEVICH, Elekrrokhimiva, 1970, 6, (IO), 1497- I502 Bond strength and H, chemisorption on Pd decrease and anion adsorption increases when Pd powder is observed in the series of acids H,SO,, II,PO,, HCl, IIHr.

Meelranism of the Chlorine Electrode Ileac- tion on Platinum, Iridiuni and Rhodium in Aqueous Aydrochlorie Acid T. Y O K O Y A M A ~ ~ ~ M. ENYO, Blectroclaim. Acta, 1970, 15, ( I Z ) , 1921-1943 The mechanism of the reaction zCl-+Cl, I.2e was studied on smooth Pt, Ir and Rh in aqueous HCl. For Pt and Ir the reaction occurs in two distinct steps; which of these is the rate determining step depends on the electrode potential. For Rh the results are incomplete.

ELECTRODEPOSITION AND SURFACE COATINGS Precious Metal Plating P. ti. L. VIVIAN, Electroplating Met. Finish.,

A review of electroplating techniques for Pd and Kh is given. The type of deposit, different methods, and the problems involved are discussed. Pt and Ru are briefly mentioned. A short account of electroless plating is also given.

1970, 23, (I I), 20-22, 24, 26, 28


The Nucleation and Growth of Electroless Metal Deposited on Plastic Substrates A. KANTBLL, Trans. Inst. Metal Finish., 1970,

A technique is described for obtaining electron micrographs of very thin electroless metal films deposited on plastic substrates. During the early stages of growth, electroless metals are deposited as island structures, growth beginning at active sites created by the SnCl, 'PdCl, treatment. I hese active Pd sites are less numerous on surfaces where the depositing metal is chemically bonded to the plastic than when it is not.

Electroplating of Osmium A. J. AITLERY, J . filectrochem. Soc., 1970, 117, (IZ), 1610 Attempts were made to form an 0 s electrode using a Au cathode, and a graphite anode in a molten electrolyte of 81,1(: OsC1, in KCN-NaCN. At 10-20 mA/cm2 a bright, adherent though granular deposit was obtained. At higher current densities black deposits occurred. Typical roughness factors for bright deposits were 6-7.

48, (51, 191-198

,-

HETEROGENEOUS CATALYSIS Reaction between Deuterium and Cyclic Olefins on Platinum/Alumina in the Liquid Phase J. J. PHILIXWN and K. L. BUKWELL, J . Am. Chem. Soc., 1970, 92, (21), 6125-6133 'The liquid phase reactions between D, and cyclopentene, cyclohexene, cycloheptene, cyclooctene, bicyclo(~,~,o)-z-octene and I-hexenc on Pt A1,0, were studied in various solvents. The exchange reaction proceeds rapidly, the D* /H* ratio increasing over the low value obtained with no solvent or in TIfF. The distribution of products and effect of solvents are discussed.

Poisoning Studies in a Single-pellet Catalytic

J. I,. HAIIN and B. 0. PETERSON, Canad. J . Chenz. lipignx., 1970, 48, (2), 147-150 The activity of a 0.25~x~ Pt/q-A1,0, catalyst was measured using the cyclopropane hydrogenolysis reaction. The catalyst was progressively poisoned from the outside to the centre plane non- uniformly. Results suggest a bi-modal pore size distribution in the pellet.

Mathematical Description of Platforniing Carried out in Severe Conditions YU. M. KHOKOV, G . AI. PANCHENKOV and I. Y A . SHAPIKO, Khim. l'ekhnol., Topliv Masel, 1970,

A matheinatical model of the reactions occurring during petroleum reforming over Pt catalysts is based on the conversions between gas, paraffins, naphthalenes, and aromatic hydrocarbons.

Reactor

(II), 37-40

Structure of Platiniim/Alumina Catalysts for Gasoline Reforming M. MOSER, L. VAJTA and I BENYI, Kent. Kozlenz.,

Electron microscopy showed the distribution of Pt in Pt,'Al,O, catalysts. Micrographs are given of Sinclair Raker 0.35':;. Pt 'A1,0, and Soviet

1970, 33, (3), 255-263

AP-56 0.55-0.60"(, I't 'Al,O,.

The Role of C5- and C,,-I)eliydrocyclisatiorr in the Aromatisation of r~-Octane on Plati- num/~llumiiia Catalyst

Nefzekhirniyu, 1970, 10, (6), 821-825 Studies of the conversion of n-octane and rz-pro- pylcyclopentanc on Pt 'A1,O:: with added alkali, ( 0 . 6 ~ ~ 0 Pt 0 . 8 ~ ) ; , Na2OJ/y-A1&L,, showed that aromatisation of n-octane is accompanied by C,,-dchydrocyclisation to form alkylcyclopcntancs in both acidic and alkaline catalysts and that, on acidic catalyst, alkylcyclopentancs play a significant part in aromatics formation. Decreasing the acidity of Pt'Al,O, by Na,O addition causes unsaturated hydrocarbons to appear in the conversion products.

Isomerisation and Dchydrocyclisation of Hexanes over Monofimctional Supported Platinum Catalysts F. M. DAUTZENBEKG and J. c. Pr.KrTmuw, .7. Caralysis, 1970, 19, (I), 41-48 Isomerisation and dehydrocyclisation reactions of hexanes in the presence of Pt,'A1,0, catalysts werc studied. The dehydrocyclisation of iz-hcxane to C,H, goes by two different routes; by a Pt- catalyscd six ring closure, or, by a thermal six ring closure of hexatrienes by dehydrogenation of n-hcxane over Pt.

Electron Microscope Investigation of Plati- num Catnlysts. I. Platinum on Aluminium Oxide I.. M. KEFI!I.I, Zh. Fiz. Khinz., 1970, 4, ( I I>, 2820-2823

The formation of Pt crystals on Als03 by the thermal decomposition of €I,PtCl, comprises the formation of a crystal lattice from Pt atoms, its coarsening, growth of these first crystals on single centres, their agglomeration, and the role of the carrier in the process.

Rheniforming Scores High in Commercial Runs G. D . GOULD and c. s. McCOY, oil G'as.7., 1970, 68, (48, Nov. 30), 49-53 The performance of Re-Pt catalysts for petroleum reforming is reviewed. They are found to maintain selectivity, to give stable yields and can bc regenerated. They have a lower fouling rate and greater stability than Pt 'A1208 catalysts. They operate efficiently at reduced pressures, which increases the yield and quality of the product.

V. G. VIASOV, YU. V. FOMICHIW alld R . A. KAZANSKII,

Mixed Adsorption Catalysts. V. Catalysis of Hydrogen Peroxide by Platinum-Silver Sys- tems on 1)iamagnetic Charcoal from Sugar I . A. Z u m v r c r r , Zh. I'iz. Khiin., 1970, 44, (IO), 2536-2540 Studies of the activity of Pt-Ag catalysts supported on batches of decalcified diamagnetic sugar charcoal in the reaction of H,O, at 23, 35 and 5 5 ' C showed that reductions in activity are caused by formation of mPt.nAg complexes on the surfice, where m and n are the simplest stoichiometric ratio. Apparent activation energies and the pre-exponential multiple in the Arrhenius equation are dircctly related but the activity of the catalysts is inversely related to them.

Contrast between Sickcl and Platinum Catdysts in IIydrogenolysis of Saturated I Iydrocarbons 11. MATSUMOTO, Y. SAITO and Y. YONEDA, .7. Catalysis, 1970, 19, ( z ) , 101-112 The mechanisms of hydrogenolysis on Ni,'SiO, and Pt SiO, are compared. The reaction on Pt occurs via heterolytic splitting of the C-H bond on adsorption. On Ni the splitting is homolytic. This is due to the greater stability of Pt-11 coordination over Ni-H coordination.

Adsorption of 15cnxene and Cyclohexane on Zeolite Y Supported Platinum Catalyst M. KOHAYASIII and T. SHIKASAKI, Kogyo Kagaku Zasshi, 1970, 73, (6), 1245-1247 The adsorption of (:,€lo and cyclohexane on Pt,'Zeolite Y catalysts containing water was studied. 'The water did not desorb on adsorption of cyclohexane, but did with C,H,. On changing the carrier gas from X, to H, adsorbed C,H, was convertcd to cyclohexane which was desorbed. The results indicate three types of catalyst site; a vacant site, sites with adsorbed water and having Pt particles, and sites with adsorbed water but no Pt particles.

Effect of the Nature and the Amount of Secondary Components of Binary Pal- ladium Alloys on their Catalytic Activity in Relation to the Dehydrogenation of Cyclo- hcxane V. M. GKYAZNOV, V. P. POLYAKOVA, E. M. SAVITSKII, L. FRADES, E. V. KARAPOVA, 8. KIIUKES and G. V. SIIKOLA, Izv. Akad. Nauk S.S.S.R., Ser . Khim., 1970, (II), 2520-2524 Studies on the catalytic dehydrogenation of cyclohexanc showed that activity increased with Pt content up to r.5'%; Pt-I'd but that it decreased with Ag content in the range 20 up to SO'^;, Ag-Pd. 51)il Ni-Pd is more active but IO~;;! Xi-I'd is less active than I'd. Apart from Pt-Pd alloys, the apparent activation energies of these alloys in this reaction are similar to that of Pd. The activity of R-Pd alloys is not large and is unstable.


Relation between Drift Potential of Cata- lyst and Reaction Rate in Liquid-phase Hydrogenation Processes. VTI. Investi- gation of the Catalytic Properties of Kaney Nickel I’romotecl by I’allacliinn v. A. DKUL’, T. D. GLADYSIIEVA and D. v. SOKCK’SKII, Kinet. Karuliz., 1970, 11, (5), 1274-1278 ‘Ihe introduction of I’d to Kancy Xi catalysts does not change the effectiveness of the catalyst surface but greatly increases its useful area, apparently because Pd increases the amount of dissolved H, and its diffusion rate. The greater number of active centres may be due to the formation of Ni-Pd centres.

Adsorption and Catalytic Yropcrties of Pallaclium-Iriclinm Electrode Catalysts A. A. SUTYAGINA, I.. G. KOPEVA and G. P.

Khini., 1970, 25, ( s ) , 562-567 A study of the adsorptive and catalytic properties of electrodeposited Pd, Ir, and Pd-Ir alloys showed that H, adsorption decreases with increasing Ir content and that catalytic activity relates to alloy composition; e.g. the catalytic activity of :-IS%, lr-Pd in hydrogenation and CH:,NO, elcctroreduction in 0.1 N II,SO, was greater than that of pure Pd or Ir.

Adsorption of IIydrogen on IIydrogenation Catalysts in Solution. V. Adsorption and Heat of Adsorption of Hydrogen on 0 s and Ku Blacks in 0.1. N €II,SO, Solutions YU. A. POIWYALIN and G. P. GRECHUSIIKISA, Zh. Fiz. Klaim., 1970, 4, (IO), 2529-2531 Charging curvcs were used to study the adsorption of H, on 0 s and Ku blacks in 0.1 N H,SO, at 0-50”

conditions than with Co catalysts. The isomeric distribution of products is not altered by the conditions in the area studied. The influence of the concentrations of the reactants and catalyst was investigated for cyclohexene.

Decarbonylation of Allylic Alcohols Using Itlioclium (1) Complexes

Tetrahedron Z2ctters, 1970, (so), 4401-4403 Ikcarbonylation of allylic alcohols, c.g. converting cis-but-2-ene-1,4-diol to I-propanol was carried out using (Ph,P),RhCl at IIO-I~O"C in aceto- and henzonitrile.

A Study of tlie Hydrogenation of Cyclo- alkenes with IIomogeneous Rhodium ( h i -

Y . TAKBUCHI, Diss. Abstr. H , 1970, 30, (IO), 4572-4573 The use of (Ph,P),RhCl as a homogeneous catalyst in the hydrogenation of cycloalkenes in a benzene or benzene-ethanol solution is reported. Effects of using different solvents and varying the ligands of the Rh(1) complex are discussed.

Speed of Homogeneous Catalytic Hydro- genation of Unsaturated Compounds with RhCI[ P(C,3€16):j]:j

197% 25, (91, 1068-1069 'The rate of hydrogenation depends on the nature of the unsaturated compound. Olefins and esters react more quickly if they contain terminal double bonds. For olefins the rates are; I-olefins . '2-ci.7- -2-truns- ,-> 3-trans-olefins; also, alkenes 1% alkynes. Substitution of a H atom by halogen decreases the reactivity.

The Reactivity of the Hydrogenation Cata- lysts MCH(CO)[I'(C~H~)~~]~~ (Me Rh, Ir) on Unsaturated Compounds w. STKOIIMEIBR and s. HOFMANN, Ibid., (II), 1309-1 3 10 The Kh complex was more active and selective than the Ir one in all cases. This behaviour, and the difference in adduct formation and dis- sociation in benzene between the two complexes is discussed in the light of increased electron density of the Ir atom over the Rh.

Further Observations on the Catalytic Transformation of Renzoic Anhydrides into Fluorenones and Ijiphenyls J. BLUM, D. MILSTBIN and Y. SASSON,J. Org. Chem.,

A study of the catalytic conversion of benzoic anhydrides into fluorenones and biphenyls by several Kh complexes indicated that mixtures of aromatic anhydrides react generally as if they were mixed anhydrides, leading to the formation of assvmetricallv substituted products.

A. BMBKY, A. C. OEIIISHIAGEK and A. M. USHAU,

plexes as Catalysts

W. STROHME:II',K and R. ENDKES, %. Nuturf. n.,

1970, 35, (IO), 3233-3237

Homogeneous Hydroformylation of Alkenes with Hydridoearbonyltris(tripheny1phos- phine)rhodium(I) as Catalyst c. K. mowN and G. WILKINSOS, J . Chem. SOC., A, Znorg. I'hys. Thcor., 1970, (17)~ 2753-2764 RhH(CO)(PPh,),, is an excellent catalyst for hydroformylation of alkenes at z5,C at I atm. I:rom alk-I-ems high ratios of straight chain to branched chain aldehydes can be produced. The dependence of rates and products on catalyst and substrate concentrations and partial pressures of H, and CO, temperature and added excess of PPh, are described.

The Protonation of Ruthenium- and Rhodium-bridged Carboxylates and Their lJse as IIomogeneous Hydrogenation Cata- lysts for Unsaturated Substances

nuDDIcI< and G . WILKINSOX, J . Chem. Soc., A, Znorg. Ph-ys. Theor., 1970, (IS), 3322-3326 The protonation of rhodium(I1) acetate by non- complexing, non-oxidising acids such as HBF4 gives the green Kh"'. The interaction with PPh, and CO gives complexes Rh(PPh,),Blj, and Rh(CO)(PPh,),HF4. The acetate Ru,(OCOMe), and its adducts with PPh, and pyridine were characterised. Methanolic HHF, solutions of Kh(1I) and Ku(I1) acetates and of Ku,(OAc),lCl in the presence of PPh, are active catalysts for the homogeneous hydrogenation of alkenes, alkynes and other unsaturated substances.

1'. LEGLDINS, K. W. MITCIlELI,, G. I.. KEMPEI., J. D.

IIomogeneous Polymerisation of Butadiene Catalysed by Ruthenium Complex-Tertiary Phosphine System K. IIIKAKI and H. HIKAI, Macromolecules, 1970, 3, (4), 382-387 Hutadienc was polymcrised using dichloro(dodeca- 2,6, I o-tricne- I, ~z-diyl)ruthcnium( 1V)- or dichloro-p- chlorobis(2,7 - dimethylocta-2,6 - diene- 1,8-diyl(diruthcnium(IV)tertiaryphosphinc catalyst. The polybutadiene had cis-1,4-, trans-1,4- and trans-~,z-unit contents of 37-60, 20-32 and 13-34"4>; the molecular weighr was 2.6-4.8 x 10,. The n.m.r. spectra of the catalysts was investigated.

CHEMICAL TKCHNOLOGY Anodic Ilischarge of Chloride Ions on Pt-Ir Alloy Electrodes G. PAITA, G. PIOKI and A. NIDOIA, J . Electrochem.

The behaviour of Ti-supported Pt-Ir alloys in the electrolysis of NaCl was examined as a function of Ir content, NaCl concentration and electrolysis time. An Ir content as low as 0.5'x1 was sufficient to eliminate the passivation effects. Not less than ~-IO(%, Ir is necessary to have low potentials after thousands of hours.

SoC., 1970, 117, (101, 1333-1335

Platirium Metals Rev., 1 9 7 1 , 15, (2) 74

ELECTRICAL AND ELECTRONIC ENGINEERING Semiconductors Produced by Doping Oxide- glasses with Ir, Pd, Kh or Ru c. c. SAKTAIS, w. D. KYDEN and A. w. LAWSON, g. Non-crystallim Solids, 1970, 4, 231 Semiconductors were produced by diffusion doping oxide glasses with more than I wt.';,,. of Ir, Pd, or Ru and by implanting 40 keV l r ions into several oxide glasses. The properties and methods of conduction in the semiconductors is discussed.

TEMPEKATUKE MEASUREMENT Kcw Reference Tables for Platinum 1 O(yo Rhodium/Platinum and Platinum 13'%, Khodium/Platinum Thermocouples - An Interim Report K . E. BEDPOKD, Z.S.A. Trans., 1970,9, (3), 248-253 Existing reference tables for Pt :Io'?,,Kh-l't and Pt : 13';&h-Pt thermocouples are known to be partially

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