MERCURY MERCAPTIDE NITRITES AND THEIR REACTION, ETC. 101

XI.-Mercury Memaptide Nitrites and tl&r Reaction with the Alkyl Iodides. Part 111. Chain Com- pounds of Sulphw.

By PRAFULLA CHANDRA RiY.

THE present communication deals mainly with a class of thio- compounds which may be conveniently termed potential mer- captans. Thiocarbamide, as also the substituted thiocarbamides,

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102 RAY: MERCURY MERCAPTIDZ NITRITES AND THEIR

thioacetamide, and thiobenzamide, may be, among others, placed under this group. It has already been shown that under the influence of suitable reagents, for example, monochloroacetic acid, iodine, etc., some of them assume the tautomeric form of imino- mercaptans, and thus become reactive (T., 1914, 105, 2159; and T., 1916, 109, 698). It occurred to the author that a class of corresponding nitromercaptides might be obtained from these by reaction with mercuric nitrite, and from the latter, again, a new series of disulphonium compounds. This anticipation has not been realised in the expected direction. The main interest in the investigation would, however, seem to centre round the fact that a series of chain compounds of sulphur has been obtained, some containing as many as six sulphur atoms. The isolation of the long expected dimercuric di-iododisulphide, I*Hg*S*S*Hg*I, has also been effected.

Thiocarbamide, for instance, under the influence of mercuric nitrite would be expected to yield the compound

thus : NH,= C( S-HgNO,) :NH,

NH2*C(SH):NH + Hg(N02), = NH2*C(S*HgN02):NH -F HNO,.

This reaction actually proceeds as indicated above, but the result- ing compound has been found to be incapable of existence as such; in the nascent stage it assumes the stable form by the conversion of the bivalent into the quadrivalent sulphur atom by fixing a molecule of mercuric nitrite, thus :

H-gN 0, 1

HgNO, I

(compare T., 1916, 109, 133). Thiocarbamide, however, yields the above compound only under

special conditions, which are described in detail later. The main product of the reaction is also a nitrite, but a purely inorganic one, having the formula 3(SHgNO,),HgO. Before we discuss its constitution further, it is necessary to add that the mono- and di- alkylated thiocarbamides, thioacetamide, thiobenzamide, as also the thiocarbimides, by reaction with mercuric nitrite yield the same substance.

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REACTlON WITH TILE ALKYL IODIDES. PART 111. 103

Mechanism of t h e Reaction.

Thioacetamide and thiobenzamide will be first considered. Under the influence of mercuric nitrite they assume the tautomeric form, thus:

R*C(:NH)*SH (where R is an alkyl or aryl group),

and the initial reaction is as follows:

R*C(:NH)*SH + NO,* Hg*NO,= R*C(:NH),S.HgNO, + HNO,.

Scission, however, takes place, as shown by the dotted line. The radicle, R*C( :NH)-, acting on three molecules of water, generates acet- or benz-aldehyde, as also the corresponding acids, with the elimination of two molecules of ammonia,

2Ll*C(:NH)* +2H,U+H~OH=R*C0H+R.CO2H+3NH,.

The radicle *SHgNO,, on the other hand, might be expected to condense to NO,HgS*SHgNB, ; the compound actually formed is, however, an oxidation product of the formula NO,HgS*O*SHgNO, ; the liberation of nitrous acid, as shown above, evidently assists this process. This compound is, however, formed only in rare instances; in nine cases out of ten the radicle assumes the more stable form, 3($HgNO2),Hg0.

Thiocarbamide and its alkylated derivatives equally yield this substance. It is only in the case of thiocarbamide, and under special conditions, that the compound shown above is formed; here also scission takes place, as shown by the dotted line, thus:

N H,* C(: N 11 ) : S- Hg NO,.

The radicle *SHgNO, becomes detached and exists in the per- manent form, 3(SHgNO,),HgO. I n the filtrate, ammonia is found in quantity; whilst in the case of the interaction of diethylthio- carbamide and mercuric nitrite, instead of ammonia, ethylamine is obtained.

It is worthy of note that in the case of mono- and di-alkylthio- carbamides no tendency towards the formation of the intermediate sulphonium oxynitrite has been observed. This is what might have been expected. The molecule, being already loaded with one Gr two alkyl groups, a t once decomposes, and does not lend itself to the formation of the cyclo-compound.

The carbimides also yield the same product, namely, 3( SHgNO,),HgO, although they cannot behave as imino- mercaptans. Here also it is the tendency of the bivalent sulphur

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104 RAY : MERCURY MERCAPTII IE NITRITES AN11 THEIR

atom to beco,me quadrivalent, that may be regarded as the under- lying principle of the reaction, thus :

The rupture takes place along the line of least resistance, and

the radicle >S<HgN''2 decomposes into the stable radicle

*SHgNO, with the evolution of nitrous fumes, whilst the organic portion of the complex RN:C < with a molecule of water yields a primary amine and carbon monoxide.

The formula of the subdance 3(SHgN02),Hg0 is only the empirical one based on analysis; it represents, however, an un- saturated compound. I n order to obtain an insight into its real constitution, the formula should be doubled, thus :

or

w?

t3 (SHgNO,) ,HgOl2

HgNQ2 HgNO, HgNO, S lIgNO, I I I I --s ----- I I I

Hg-0S .W &&,; :NO, No.'O-Wg

SS-HgNO, = NO,Hg .,3. S---- s--

HgNO, YgNO, Yg-NO, IIgNO, I 1

I I I N 0,Hg S * S --S---S--S*S*H gNO, + 2 N,O,.

H g O---- Hg--- G I n other words, as soon as there is an opportunity for the formation of the stable radicle .SHgNO,, every three of these take up an additional molecule of mercuric nitrite (that is, the radicles HgNO, and NO,), and the two complexes coalesce into a single molecule with the evolution of two molecules of nitrogen trioxide.

On a previous occasion (T., 1916, 109, 133), in explaining the formation of the compound Et$32Hg(N0,),,Hg0 by the interaction of ethyl disulphide and mercuric nitrite with the evolution of nitrous fumes, it was assumed as a working hypothesis that the two ato'ms of bivalent sulphur became quadrivalent. I n the present) investigation this hypothesis has been elaborated and found t o hold good throughout, not only in explaining the formation of the compound under discussion, but also that of the compound NH,*C(:NH)*S*HgNO,, and also the reaction between thiocarb- imides and mercuric nitrite. The hypothesis, being in conformity with d l the observed facts, now stands on a solid foundation.

By treating the compound, Hg,S30,N3, which is highly reactive, with the alkyl iodides, Borne interesting chain com- pounds of sulphur have been obtained, notably one of three sulphur atoms, having the formula HgI*SEtI*S*SEt, in which one

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REACTION WITH THE ALKYL IODIDES. PART 111. 105

sulphur atom is quadrivalelit and the remaining ones bivalent, and dimercuric di-iododisulphide.

It is the affinity of the sulphur atom for the radicles *HgI and -HgNO, respectively tha t may be regarded as the underlying prin- ciple in the formation of derivatives of this type. From analogy, also, one might have expected a compound of the formula NO,Hg*S*S*HgNO,, and not NO,Hg-S*O-S*HgNO,~ b u t the mode of its formation, as also of dimercuric di-iododisulphide, explains the *difference in their constitution. The former is produced by ' wet ' reaction in the presence of nascent nitrous acid, which acts as a powerful oxidising agent, whereas the latter is the product of a reaction which precludes the possibility of oxygen taking any part whatever.

It will be noticed that, whenever there are more than two atoms of sulphur in a molecule, some (but Rot all) can become quadri- valent. Thus the sulphonium derivative of ethylene mercaptan, empirically formulated as (C,H,S,),,HgI,,EtI, should be repre- sented as

,S- s, O,H,( HgI Et\C,H,,

\S--d,/ 5 I /

t- t in wliicli formula only two of the four sulphiir atoms are quadri- valelit) (T., 1916, 109, 605). The componnd

has only one quadrivalent sulphur atom, whereas in the compouiicl I3( SHgNO,),HgO],, containing six sulphur atoms, the two extreme members in the long chain are bivalent, the intermediate ones being quadrivalent. I n connexion with this, it is of interest, to note tha t Auld, in his recent investigation on alkali polysulphides (T., 1915, 107, 480), suggests t ha t calcium polysulphide should be forinu-

lated as Ca<ll>S:S:S:, t ha t is, the sulphur atoms a t one end of

the chain are quadrivalent, whilst the atom a t the other end is b i v a1 en t ,

Methyl iodide, when heated on the water-bath in contact with the above complex inorganic oxynitrite, yields as the main pro- duct, besides nitromethane, the compound Me2S,,Hg12,MeI, which has been previously described (T., 1916, 109, 606) as having been obtained by treating mercury methylmercaptide nitrite with

s S

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106 RAY: MERCURY MERCAPTIDE NITRITES AND THEIR

methyl iodide. The present reaction, however, is of interest, inasmuch as a purely inorganic salt, and not a nitromercaptide, yields a compound of the disulphonium series. When the higher alkyl iodides are substituted, the reaction assumes various degrees of complexity.

It may be added here that the compound Et,S,Hg(NO,),,HgO, when heated with ethyl iodide is converted into the corresponding disulphonium compound, Et,S2HgI,,EtI.

E X P E R I M E N T A L . Interaction of Mercuric Xi t r i te and Thiocarbamide.

A very dilute, aqueous solution of thiocarbamide is added in a thin stream from a 5 C.C. pipette, with constant shaking, to a fairly concentrated solution (about 100 c.c.) of mercuric nitrite (in the shape of sodium mercurinitrite; T., 1907, 91, 2031). A curdy, whitme precipitate is formed, which should be collected a t once; the operation should, in fact, be performed within five minutes. The filtrate is set aside, when i t begins slowly to deposit a yellow, heavy, granular powder; to i t is now added from time to time, at intervals of twenty minutes to half an hour, 5 C.C. of the tliiocarb- amide solution as before. Successive crops of the yellow salt are thus continuously obtained. The reaction should be allowed t o proceed for several hours. During the course of the reaction bubbles of gas are given off, and the odour of nitrous fumes is distinctly perceptible.

The curdy, white precipitate as obtained above, when dried in a vacuum over sulphuric acid, assumes a very faint yellow tint. It has the constitution

HgNO, NH,*C(:NH)-S--Hg

\/

I

0 and dissolves in hydrochloric acid, evolving nitrous fumes :

Found : C = 2-00. 0.1222 gave 7.8 C.C. a t 3 2 O and 760 mm. 0.1004 ?, 0.0872 HgS and 0.0414 BaSO,. Hg-74.87;

CH303N,SHg, requires C=2*23; N=7.82; S=5*96; Hg=74*49 per cent.

The cornpoutid [3(SHgNO,),HgO], is, as explained above, the stable modification of that obtained by the interaction of mercuric nitrite and thiocarbamide. The substituted thiocarbamides, thio-

N=7.00.*

S = 5.66.

* Another preparation gave N = 7.17.

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REACTION WITH THE ALKYL IODIDES. PART III. 107

acetamide, thiobenzamide, and the thiocarbimides yield only this variety, to the exclusion of the former. As it was difficult t o believe that the product obtained in each case was an inorganic salt of identical composition, it was subjected repeatedly t o com- bustion analysis, but the amount of carbon was negligible, as it varied from 0.2 to 0.5 per cent. This is no doubt due t o traces of the organic reacting agents being co-precipitated.

The compound is heavy, granular, and yellow, and can be dried in a steam-oven. It is insoluble in water o r acetone, but dissolves in hydrochloric acid, especially on warming, with effervescence and copious evolution of nitrous fumes. When boiled with water, it decomposes and is converted into black mercuric sulphide :

0-1206 gave 0.1065 HgS and 0.0742 BaSO,. Hg=76*13;

0-1328 gave 0.0838 BaSO,. S=8-66. 0.1172 ,, 3.8 C.C. N, a t 3 1 O and 760 mm. N=3*60. [0*2028 ,, 0.0012 CO, and 0.0036 H,O. C=0*16; H=0*20.] Hg,S30,N3 requires Hg = 76.19 ; S = 9-14 ; N =4.00 per cent.

If this compound, instead of being removed, is left in contact with the mother liquor for a week, or sometimes even for a forb night, it slowly undergoes a remarkable change in composition, a dull red, and on some occasions a scarlet, modification of mercuric sulphide being produced. The formation of the dull red, as also of the crystalline, form of the sulphide by the wet process has not, so far as we are aware, been previously noticed.

An analysis of the red sulphide, necessarily impure, gave Hg = 83-43, S = 14.29, whilst theory requires Hg = 86.20, S = 13.80 per cent.

When diethylthiocarbamide is used in the reaction, a compound of the formula NO,Hg-S*O*S*HgNO, is occasionally also formed :

0.1010 gave 0.0810 HgS and 0.0760 BaSO,. Hg=6*14;

0.1694 gave 5.2 C.C. N2 a t 2 9 O and 760 mm. Hg2S20,N2 requires Hg=69.94; S=11*19; N-4-90 per cent.

S=8.45.

S = 10.34. N=3*44.

Interaction of Mercuric Nitr i te and Allylthiocarb imide.

I n this preparation particular care should be taken not to add an excess of the thiocarbimide. The following method is recom- mended. A very dilute solution of allylthiocarbimide in alcohol is added in a thin stream, with constant shaking, to a fairly concen- trated solution of the nitrite. If the former happens t o be present even in slight excess the precipitate a t once turns black, and is

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108 MERCIJRY MERCAPTTDE NITRITES ANT, THETR REACTION, ETC.

ultimately converted into mercuric sulphide. nitrous fumes are evolved.

During the reaction

The presence of allylamine in the filtrate was proved.

Interactioi,, of tire Compound I3(SHgNO,),HgO], rind t he A 7kyl lOdideS.

(a) M c f i ~ y l Zod&-As pointed out above, methyl iodide yields the disulphoniurri coitipound, Me,S,,HgI,,n'IeI. The method of procedure is exactly the saine as in the interaction of mercury mercaptide nitrites and the alkyl iodides. The product, purified by precipitation from its acetone solution with ether, melted a t 162O :

0.1552 gave 0.0296 CO, and 0*0200 H,O. 0.0864 required 23.1 C.C. AgNO, solution in acetone=3'78 C.C.

0.1872 gave 0.0550 Hg. Hg = 29.38. C,H,I,S,Hg requires C = 5-22 ; H = 1.30 ; I =55% ; Hg= 28-95

(b) Ethyl lodide.-In this case the reaction is by no means so simple as above; the mother liquor contains nitroetliane and un- changed ethyl iodide, and when it is evaporated a deposit' of red mercuric iodide is left. The yellow residue in the flask is repeatedly exhausted with acetone, which dissolves the organic constituents. The insoluble portion consists mainly of impure diiriercuric di-iodo- disulphide, I*Hg*S*S*Hg*I.

The acetone filtrate on evaporation gives a mass of yellow crystals, and by careful fractionation a product melting a t 86---88O can lie separated. I t approximates t o the formula Et,S,HgT, or

C=5*20; H=1*43.

N / lO-AgNO,=O.O48O I. I = 55-60.

per cent.

IIgI E&S-S*E~ .

1 1

Small quantities of the compound Et2S2,HgI,,EtI (in. p. 1lao), and another substance with a higher melting point, are also' among the products. It is not, however, easy to obtaiii thein in a pure state.

Analysis of the Substance Melt ing a t 86-88O.

0.1372 gave 0.0378 CO, and 0-0351 H,O. 0.2412 ,, 0.0760 Hg, 0.1947 AgI, and 0.2374 BaSO,.

02234 gave 0.0708 Hg. Hg=31-69.

C=7*51; H=2-84.

Hg=31.51; I=43*62; S=13*52.

C,H,,T,S,Hg requires C = 7-89 ; H = 1-64 ; Ng = 32.89 ; I = 41:77 ; S = 15.79 per cent.

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AZOXYC.4TECHOL ETI-IERS AND RELATED SUBSTANCES. 10'3

Dimercuric di-iododisulphide, as prepared in the above manner, is always contaminated with some of the unchanged compound, [S(SHgNO,),HgO],. It was therefore dried, powdered, and boiled with ethyl iodide, this process being repeated, and after each treat- ment with ethyl iodide the product was repeatedly exhausted with acetone so as to remove the soluble constituents referred to above:

0.2616 gave 0-1480 Hg. Hg=56*59. 0.2374 ,, 0.1346 Hg and0.1565 BaS04. Hg=56*170; S=9.05.

Hg,I,S, requires Hg=55*71; S=8*91 per cent. Dimercuric di-iododisulphide is a pale yellow, granular powder.

It slowly darkens in diffused daylight; on exposure to direct sun- light this process is hastened, but when kept in the dark the original yellow colour is restored. Similar instances of reversible phototropic properties are only met with in the class of organic colouring matters known as the fulgides.

I avail myself of this opportunity t o express my siiicere thanks to Mr. M. L. Dey, M.Sc., for his ungrudging help in the tedious estimation of sulphur in these conipouncls and for some suggestions as t o their constitution.

CHEMICAL LABORATORY, PRESIDENCY COLLEGE, CALCUTTA. LRccciucd, JLirie Z ' i t h , 19lti.J

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