VARYING VALENCY OF PLATINUM, ETC. 133

XVL- Varying Vulency of Platinum with Respect to Mercaptanic Badicles.

By SIR PRAFULLA CHANDRA RAY. TEE chloromercaptide (EtS),PtCl, containing tervalent platinum, obtained by the interaction of platinic chloride and ethyl mercapt,an (T., 1919, 115, 872), is also produced from diethyl disulphjde under similar conditions ; during the reaction chlorine is evolved :

Et*S*S*Et + PtCl, + (EtS),PtCI.

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134 RAY : VARYING VALENCY OF PLATINUM

An alternative explanation is that, on account of its greater affinity for sulphur, the platinum not only parts with three of its chlorine atoms but has its additional latent ralencies revived, the chloromercaptide being in reality a derivative of quinquevalent

platinum and a sulphonium compound, Et .g>PtCl.

The quinque- and the sexa-valency of platinum are established by the compounds, (C,H4),S2,PtC13 and (C,H4),S3,PtC1,, already described (T., 1923, 121, 1283); these are examples of the sul- phonium derivatives which the author has been investigating during the last seven years. Diethyl sulphide also yields with platinic chloride two chloromercaptides having the empirical formulze (Et,S),PtCl, and (Et,S),YtCI,.* The former has been obtained in well-dehed crystals and has been proved in acetone solution to be a non-electrolyte. Cryoscopic molecular weight determination in benzene solution also confirms the same conclusion.

1 : 4-ThiazanY S<C2H4>NH, C H yields with hydrogen chloride the

expected hydrochloride, C,H,NS,HCl. Davies finds' that the compound with platinic chloride has the formula, B,HCl,PtCl, (T., 1920, 117, 29s) and he erroneously regards it as the chloro- platinate of the base; had it been so, it should have conformed to the formula (B,HCl),,PtCl,. The compound in questlion is possibly a chloromercaptide, having the formula C1,Pt :S<C*H4>NH,HCl, C H

in which platinum is sexavalent. Direct evidence of the variation in the valency o€ platinum has

been obtained by the interaction of platinic chloride and the following mercaptans or rather their potassium salts, which have been found to be more reactive :-( 1) 2-thiol-5-thio-4-phenyl-

4 : 5-dihydro-1 : 3 : 4-thiodiazoleY ~Ph">t?*SH, and (2) dithio-

ethylene glycol, C,H,( SH)2.

Et-S

2 4

2 4

c s---s

* These can be represented on the basis of Wemcr's co-ordination theory :

or, according to TschugaeiT and Subbotin (Bey. , 1910, 43, 1200),

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WITH RESPECT TO MERCSPTANIC RBDICLES. 135

Tt: rval ent PI ai; i imm . The product of interaction in each case has been found to be n

well-defined compound, which admits of reproduction under the conditions of formation; these have been studied with great care. It; has already been shown that if to a concentrated aqueous solution of the potassium salt of the above thiodiazole a dilute solution of chloroplatinic acid is added in a thin stream, a product is obtained which coiisists of a mixture of equal proport,ions of compounds of tervalent and bivalent platinuiii (T., 1919, 115, 875); by suitably adjusting the concentrations of the participants, the compound of tervalent platinum has now been isolated in a state of purity. By slightly modifying the process, the corresponding chloromercaptide has also been obtained.

Ter-, Quadri-, Quinque-, Xexa-, and Och-valenzt Platinum. The niercaptan most suitable to the preparatioii of this series is dithioethylene glycol; although it is a dithiol, only one atom of hydrogen of the thiol groups is replaceable by potassium. The substitution of an atom of potassium seems to exercise a sort of inhibitory influence on the second hydrogen atom of the thiol group -in fact, the latter becomes so inert as not to be assailable by the chlorine atoms of platinic chloride. Even chloropicrin, which is a very reactive agent, yields with the mercaptide only the compound [(SH*C,H,-S),C],O (T., 1919, 115, 1308). ~~-

In the present instance, the reaction takes place as follows :- -

xSH*C,H,*SK + PtCl, --f Pt(S*C,H,*SH),, where x = 3, 4, 6, 6, or 8. By using solutions of the reagents of definite strengths and regulating the temperature of the reaction, compounds have been obtained in which platinum functions as ter-, quadri-, quinque-, sexa-, and octa-valent, respectively. For instance, at the tempera- ture of the laboratory (25-30") sexavalent platinum compounds have generally been obtained; but by suitably varying the con- centrations of the parent solutions, quinquevalent compounds have been secured at this temperature. If, however, instead of changing the strength of the above solutions, the temperature of the solution of the potassium salt be reduced to 5-15' (the platinic chloride solution being kept between 25-30'), only octavalent compounds will be produced; similarly, by regulating the range of temperature between 60' and 65", quinquevalent compounds are formed; at about 80", quadrivalent ones are obtained, whereas at about 100" the product is uniformly tervalent. At intermediate temperatures mixtures are formed. These reactions have been repeated in almost all cases two to three dozen times under the

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136 U Y : VARYINQ VALENCY OF PLATINUM

above conditions, with identical results. In fact, it has been well established that the particular valency which platinum will assume is a function of either of the two variables, concentration and temperature.

This result might well have been expected from a consideration of the kinetic theory of molecules. As increase of temperature h s the effect of increasing the mobility of the molecules, the platinum atom is not placed in a favourable position to attract its full quotum of mercaptanic radicles. Conversely, if the temperature of the solution is lowered, the molecular velocity will diminish and con- sequently the platinum atom will be in a position to develop its maxi- mal group valency. It is also a well-known fact that increase of temperature tends to dissociate complex or heavier molecules into simpler ones, and the particular instance here in the case of com- pounds of platinum, the complexity of which diminishes with increasing temperature, falls within the scope of this general observation. In other words, the higher the temperature of reaction the lower the valency of platinum.

The place of platinum in the periodic table would naturally lead us to expect that, like iridium, it should behave as tervalent and, like osmium, as quadri-, sexa-, and octa-valent. Ruff and Tschirch have shown that the formation of the fluorides, OsF4, OsFE, OsF,, depends on the temperature, the rate of flow of the fluorine current, and the particular physical condition of the osmium (Ber., 1913, 46, 929), and this fact is fairly well borne out in the case of the platinum derivatives which form the subject of the present communication.

It is not easy to give equations of the reactions involved in the formation of the above compounds and to account for the vari- ation in the valency of platinum. The interaction of diethyl disul- phide (Et,S,) and chloroplatinic acid results in the formation of the compound (EtS),PtCl with evolution of chlorine. As diethyl disulphide itself results from the oxidation of ethyl mercaptan, the liberated chlorine cannot further act on the former and hence the presence of any impurity in the shape of oxidation product in this chloromercaptide is precluded. Platinum is evidently tervalent in this compound. When, again, chloroplatinic acid acts on potassium thiazole, the platinum parts with all the chlorine atoms, but contrary to expectation a derivative is obtained in which the metal functions as tervalent. Of course by doubling the formula the metal may be represented as quadrivalent ; when, however, it is borne in mind that the chlorides of iron and iridium, the analogues of platinum in the t,ransitional group, have the simpler formulze FeC& and PrCl,, respectively, it is scarcely likely

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WITH RESPECT TO MERCAPTANIC RADICLES. 137

that the platinum mercaptide should have a more complex formula. Similar arguments would support the formula (SH*C,H,*S),Pt for the dithioethylene glycol derivative. The formation of quadrivalent platinum mercaptide may naturally be expected ; it is not easy to account for the existence of quinque-, sexa-, and octa-valent mercaptides. From considerations of the physical properties of chloroplatinic acid, for example, ionisation, absorption spectrum, and heat of neutralisation, the formula H,PtCl6 assigned to it. As a working hypothesis, the formation of the above compounds may be explained according to the following equations, although objection may be raised that no direct proof of the evolution of hydrogen is available :

10SH*C2H,*SK + 2H,PtC16 = 2Pt(S*C,H,*SH)5 + 6SH*C2H4*SK + H,PtCl, = Pt(S*C2H4*SH)6 + 6KC1 +H2 . (2) 6SH*C2I-I,*SK + 2SH*C,H4*S[H] + H&?tcl6 =

Pt(S*C,H,*SH), + 6KCl + 2H, . . (3)

10KC1+ 2HC1+ H, . . (1)

In the last reaction, the two molecules of free mercaptan are produced by the hydrolysis of two molecules of potassium mer- captide, the motive of the reaction being the affinity of the sulphur atom of the univalent radicle SH*C,H,*S* for platinum, and hence in the formation of the octavalent compound the hydrogen atom shown in brackets is displaced so as to enable the sulphur atom to enter into direct relatlionship with the metal, and satisfy its maximum valency. It is well known that certain radicles, simple or compound, enable certain elements to develop their maximum latent valencies. Thus sulphur, which in regard to chlorine is either bi- or quadri-valent, behaves as sexavalent when combining with fluorine or iodine ; platinum in respect to the radicle SH*C,H,*S. thus has varying valencies depending on the temperature and concentration of the latter.

On the other hand, it might be urged that chloroplatinic acid would act as if it had the formula PtC14,3HC1; there is then the possibility of chlorine being liberated, in some instances a t any rate, which would oxidise a portion of the dithioethylene glycol to (C,H,S,), ; the latter, being insoluble in ordinary solvents, .might be expected to contaminate some of the products. The presence of this oxidation product is, however, highly improbable. Let it be supposed that the reaction is only quantitative in the case of quadrivalent platinum and that the other products are merely mixtures. These, according to the results of the actual experiments, should be represented as

F*

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138 R,AY : VARYING VALENCY OF PLATINUM

Pt(S*C,H,*SH), $- .'c ; Pt(S*C,H,*SH), + 2~ ; Pt(S*C,H,*SH), + 4~ ; where x = C2H4SZ."

In other words, the amount of the impurity occurs in exact multiple proportions of the molecule C,H,S,. In mixtures, however, one would expect the impurity to occur in indefinite proportions.

Another equally untenable position to which the above sup- position would lead is that the lower the temperature of the reaction the larger the amount of the oxidation product, the insximum oxidation taking place at 5-15' and the minimum at loo", that is, at the temperature yielding the tervalent platinum compound. The presence of any accidental foreign substance thus seems to be out of question. Indeed the octadic character of platinum, far from being an anomaly, is to be welcomed as justifying its place in group viii of the periodic system.

E X P E R I M E N T A L . Tervalent Platinum.

Thiodiaxole and Platinic Chloride.-To 0-5652 grain of the potass- iuiii salt, dissolved in 10 C.C. of water, were added with stirring 2 C.C. of chloroplatinic acid (1 c.c = 0.0301 Pt). The flocculent, orange precipitate obtained was washed with water, dried in a vacuum desiccator, powdered, and treated successively with hot alcohol and benzene (T., 1919, 115, 876) to extract the impuri- ties (Found : Pt = 22.62; S = 31.88. C,,H,,N,&Pt requires Pt = 22.59; S = 33-03 per cent.). If, however, dilute solutions of the reactants be used, a chloromercaptide will be formed (see under quinquevalent platinum).

Dithioethylene Glycol and Plutinic Chloride.-The m d u s operandi is the same as described under sexavalent platinum, the temper- ature of the mercaptide solution being, in this case, about 100" (Found : Pt = 41.05 ; S r= 39.66 ; C = 15.24 ; H = 3.31. C,HlSS6Pt requires Pt = 41.13; S = 40.51 ; C -1 15-13; H = 3.15 per cent .) .

Quadrivalent Platinurn. Dithioethylene Glycol and Plutinic Chloride.-The quadrivalen t

compound of platinum produced by the interaction of dithioethylene glycol and platinic chloride has already been described (loc. cit., p. 876); but in the present instance the potassium derivative of the mercaptan was employed. By using it in the same concentration as in the cases of ter-, quinque-, sexa-, and octa-valent derivatives, but increasing the temperature to 80', the desired

* Analysis cannot discriminate between SHC,H,-S and C,H,S,, the differ- eiice being onIy one atom of hydrogen.

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WITH RESPECT TO MERCAPTANIC RADICLES. 139

compound was obtained (Found : Pt = 34.34; S = 45-68 ; C = 16-57 ; H = 3.33. C,H,,S,Pt requires Pt = 34.39 ; S = 45.14 : C = 16.93; H = 3.54 per cent.).

Triethylene Trisulphide and Platinic Chloride.-The product of interaction is a crystalline compound conforming to the formula (C,H,),S,,PtCI,, in which platinum behaves either as tetrad or hexad (see above).

Quinquevalent Platinum. Diethyl Disulphide and Platinic Chloride.-When an alcoholic

solution of the components is heated under reflux on the water- bath for three to four hours, the solution gradually becomes turbid, an orange precipitate forms, and chlorine is continuously evolved. The compound has the empirical formula (C,H,*S),PtCI, but in reality it is a pentad derivative of the metal. The same compound is also formed in the cold when a concentrated alcoholic solution of the parent substances is set aside for twenty-four hours or more [Found : Pt = 64-51 ; C1 = 9-95; S = 18.11. Pt(C,H,*S),Cl requires Pt = 55.02; C1 == 10.09; S = 18-19 per cent.].

It is, in fact, the same compound which has already been described as formed by the interaction of ethyl mercaptan and chloroplatinic acid. If instead of this simple mercaptan one with a complex radicle, for example, thiodiazole, be used, a corresponding chloromercaptide will be obtained.

Thiodiazole and Plutinic Chloride.-To 4 C.C. of diluted chloro- platinic acid (= 0.0400 gram Pt) were added drop by drop with constant stirring 7.5 C.C. of a dilute solution of the potassium salt (= 0.1058 gram). The precipitate was washed with water, dried in a vacuum, and treated successively with alcohol and benzene (Found : Pt = 28-19; CI = 4-86. C,6H,,N4C1S6Pt reqUkeS Pt = 28.86 ; C1 = 5.00 per cent.).

Triethylene Trisulphide and Platinic Chloride.-The trisulphide has also been shown to yield another compound with platinic chloride which has the formula (C,H,),S,,PtCI,, one atom of sulphur being detached from the trisulphide during reaction. The platinum here may be regarded as ter- or quinque-valent.

Dithioethylene Glycol and Plutinic Chloride.-To 0.4330 gram of the potassium salt, dissolved in 8-4 C.C. of water a t the ordinary temperature (25-30°), were added with vigorous shaking 23 C.C. of platinic chloride solution (1 c.c = 0-0067 gram Pt). The light brown precipitate was treated as described under sexavalent platinum. The same compound was obtained when the experiment was conducted under the same conditions as given below under sexavelent platinum, the only variation being that the temperature

I?* 2

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140 R&Y: VARYING VALENCY OF PLATINUM, ETO.

was kept between 60-65" (Found : Pt = 29.78; S = 48.01 ; C = 18.46 ; H = 4-54. CPOH25S10Pt requires Pt = 29.54 ; S=48*50 ; C = 18-13; H = 3.78 per cent.).

Sexavalent Platinum. As the mereaptide, C,H,(SH)(SK),* is the parent substance from

which most of the derivatives of platinum have been obtained, and as it has not been described before, its preparation is given here in detail. A large excess of concentrated alcoholic potash is added to dithioethylene glycol. The mixture, which solidifies when stirred, is rapidly filtered with suction, and the solid washed with alcohol. Care should be taken to limit the quantity of alcohol used, for the potassium salt is appreciably soluble in that menstruum. The solution remains clear only for about half an hour and then begins to turn turbid owing to aerial oxidation and the formation of the disulphide, C,H,S,.

Dithioethylene Glycol and Plat inic Chloride.-The hexad deriv- ative is the one which was almost invariably formed when about 12 C.C. of platinic chloride solution (1 C.C. = 0.0260 gram Pt) were added to 0.5500 gram of the potassium salt of dithioethylene glycol, dissolved in 15 C.C. of water a t temperatures between 25-30'. The platinum chloride solution was introduced in a thin stream into the vigorously a3gitated liquid and the operation was finished in less than five minutes. The granular, light-brown precipitate was vigorously shaken, and a large volume of water added to the mixture to preclude the possibility of the formation of potassium chloroplatinate. It was washed first with water, then with alcohol, and finally with ether, and dried in a vacuum over sulphuric acid (Found : Pt = 26.00; S = 51.40; C = 18.94; H = 3.40. C,,H,,S,,Pt requires Pt = 26.09 ; S = 50.55 ; C = 19.07 ; H=3.97 per cent . ) .

Diethyl Sulphide and Platinic Chloride.-A concentrated alcoholic solution of the above two components was set aside for two to three days. The crystalline products which were obtained were dissolved in boiling alcohol. The crop which was deposited on cooling con- formed to the formula (Et,S),PtCl, and had the m. p. 198". On concentration of the mother-liquor, the product of the formula (Et,S),PtCl,, M. p. 77", was obtained t (Pound : Pt = 44.01 ; C1 = 16.05. Calc. for C8H,,Cl,S,Pt, Pt = 43.97; C1 = 15.85 per cent .) .

* Analysis of the potassium salt. C,H,S,K requircs K = 29.55 per cent.

7 Both these compounds have already been described, Lut the method of formation was quite different (Juhresber., 1888, I, 1419; Tschugaeff, Eoc. cit.).

Found : K = 29-99.

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PRENYLTRIMETHYLAMMONIUM PERHALOIDS. 141

Oct avalent Platinum. Dithioethylene Glycol and Platinic Chloride.-The conditions of the

experiment were almost the same as described under sexavalent platinum, the only difference being that the temperature was kept at 5-16" (Found : Pt = 21.00; S = 54-79; C = 19-97 ; PI: = 3.89. CI6H,,,S,,Pt requires Pt = 20-94 ; S = 54-41 ; C = 20-36 ; H=4-25 per cent .).

The absence of chlorine was proved in all these compounds. Diethyl Xulphide and Platinic Chloride.-The preparation of the

compound ( Et28),PtC1, has been described under sexavalent platinum [Found : Pt = 37.64; C1 = 27.20; M , by the cryoscopic method (in benzene), = 540. C8H2,C1,S,Pt requires Bt = 37.96; Cl = 27.36 per cent.; H == 519.1

CHEMICAL LABORATORY, COLLEGE OF SCIENCE,

UNIVERSITY OF CALCUTTA, [Received, April 3rd, 1922.1

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