NITROMERCAPTIDES AND THEIR REACTION WITH ALKYL IODIDES. 131

S I.--.Nitr.omercixptides and their Reactio~a with the Compounds of the Disulphoniuwa Alky l Iodides.

Se r ips. By PRAFULLA CHANDRA RAY.

THE reactivity of the mercaptans towards the mercury haloids is well known. Ethyl mercaptan, f o r instance!, readily acts on mer- curic chloride and iodide, giving rise to the formation of the compounds EtS*I?gCl and EtS-HgI, which may be termed chloro- and iodo-mercaptide respectively. I n the course of previous investigations the close analogy which obtains between mercuric chloride a-nd mercuric nitrite has often been pointed out (T., 1912, 101, 965). So close is this analogy that when a compound of mercuric chloride with an alkylamine is obtained a corresponding one with mercuric nitrite can almost be predicted (T., 1913, 103, 3). The explanation lies in the fact that both these salts are very feebly ionised in aqueous solutions. Recently it occurred to1 the author that mercuric nitrite when treated with the mercaptans might yield a series of nit'romercaptides. The expectation has been realised, but the phenomenal reactivity of mercuric nitrite with regard to the mercaptans results, not only in the formation of nitromercaptides of the type R*S*HgNO, (R = alkyI), but also of compounds of the type R*S*HgNO,,Hg(NO,),, that is, both sub- stitutive and additive products (P., 1914, 30, 140), and often mixtures of both in varying proportions. The subject has recently been more thoroughly and systematically investigated, with the result that, not only has the new and interesting series of the expected organic nitrites been isolated in a state of purity, but additional light has been thrown on their const,itution by their behaviour towards the alkyl iodides.

Although from their mode of formation, described in detail below, there is scarcely any room for doubt that these mercapkides conform to the constJtutiona1 formula R*S*HgNO,, it was thought

a* 2

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132 RAY : NITROMERCAPTIDES AND THEIR

desirable further to settle this question by acting on them with the alkyl iodides ; ethyl nitroniercaptide’, for instance, would be expected t o actt on, say, ethyl iodide in the following manner :

the products being ethyl disulphide, mercurous iodide, and nitro- ethane. This is what actually happens, only in place of mercurous iodide, mercuric iodide is formed, the extra atom of iodine being derived from the ethyl iodide itself, which might decompose under favourable conditions. The most notable feature of the reaction, however, is that the ethyl disulphide, a t the moment of it5 forma- tion, combines with a molecule of mercuric iodide) and another of ethyl iodide, which is always added in excess, to form an additive compound of the empirical formula, Et$3,,Hg12,Etl, in the shape of glistening, yellow tablets. Simultaneously, a t least two more compounds are formed, consisting of the above components, but evidently in different proportions, but i t is not an easy task to isolate the latter in a state of purity. Methyl mercaptide also behaves similarly, and the various other alkyl iodides may also be substitated for ethyl iodide, the reaction being of general applicability, salts of the type R,S,,HgI,,R’I being invariably formed, where R and R’ represent different alkyl radicles.

A t first sight these1 compounds appear to be simply “ molecular’’ and of an additive character, but in reality they are derivatives of the sulphonium series with t’wo sulphur atoms in the chain. Smiles has shown that mercuric iodide dissolves readily in contact with alkyl sulphidee, generating well-defined salts of the empirical formula RIt’S,HgI,, and he suggests that these are t o be regarded as sulphouium mercuric iodides. I n the presence of mercuric iodide the bivalent sulphur becomes quadrivalent, and he f ormu- lates these compounds as SRR’IgHgI (T., 1900, 77, 161 ; 1907, 91, 1396).

The key t o the constitution of the present series of compounds is furnished by an extension of Smiles’ hypothesis t o the alkyl disulphidee. In the presence of mercuric and alkyl iodides the two bivalent sulphur atoms of the alkyl disulphide become quadri- valent, thus favouring the formation of salts of the type

SRR’I*SRI*HgI. The reactivity of mercuric nitrite equally favours the formation

of sulphonium derivatives with one and two atoms of sulphur respectively. F o r instance, ethyl sulphide has been found to yield a compound of the formula Et,S,Hg(NO,),, which should be regarded as a sulphonium mercuric nitrite, hTO,-SE~*HgNO,. When ethyl disulphide is acted on by mercuric nitrite, nitrous fumes are evolved and a white, crystalline nitrite is obtained, con-

2EtS.HgN02 + 2EtI = EkS, + Hg,I, + 2EtN02,

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REACTION WITH THE ALKYL IODIDES. 133

forming to the formula Et2S,,Hg(N0,),,Hg0. The reaction becomes almost inexplicable if this compound is regarded simply as an additive one, as nitrous fumes may be expected to be disengaged whenever mercuric nitrite acts on a mercaptan, thus:

mSH + Hg(NO,), = *S*HgNO, + HNO,. I n the present instance there is no room f o r such a reaction. What evidently happens is that both the bivalent sulphur atoms become quadrivalent, thus : Et.S*S*Et, and two molecules of mercuric nitrite are now fixed, giving rise t o the hypothetical compound:

vo2 EtS------ $Et

I"3, ONIO*Hg I I

As the chain i.s lo,aded nitrite, however, it has

YgNO? Y O 2 EtS------;SEt + N,O,.

I I 0--- Hg

with heavy radicles derived from mercuric t o part witlh a portion of the latter in ' the

shape of nitrogen trioxide, generating a compound, which is a t once a disulphonium salt and a cycloid. The formation of this interesting oxynitrite as suggested above, not only brings it into line with the proposed constitution of the disulphonium series of mercuric iodides, which forms the1 subject matter of the present communication, but may also be taken as a further confirmatory proof of this. These evidently contain one or two, as the case may be, asymmetric sulphur atoms. It should be possible to resolve them into their enantiomorphs by suitable methods. It is note- worthy that Hilditch and Smiles treated ethyl disulphide with a mixture of ethyl iodide and mercuric iodide in acetone solution and obtained a series of sulphonium iodides of entirely different fomula+--all of them being derivatives of a single sexavalent sulphur atom (loc. c i t . ) .

EXPERIMENTAL. Nitromercapt ides.

Ethyl Nitromercnptide, EtlS*HgNO,.-A dilute alcoholic solu- tion of the mercaptan is added with constant stirring t.0 a fairly concentrated solution of sodium mercuric nitrite, care being taken that the latter is always in excess. After an interval of a minute or two a crystalline, nacreous precipitate, with a faintly yellow tint, is obtained. During ths reaction the solution becomes warm and nitrous fumes are liberated. The salt is washed and dried, preferably in a vacuum, over sulphuric acid. If the mercaptan solution is concentrated and if i t is added all a t once to the mercuric nitrite solution a pasty mass and sometimes a grey pre- cipitate is the product, which on analysis is found to be a mixture of different salts. Ethyl nitromercaptide dissolves readily in hydro-

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134 RAY : NITROMERCAPTIDES AND THEIR

chloric acid with the evolution of nitrous fumes and the garlic-like odour of mercaptans. It is almost insoluble in water; 20 C.C. of water a t 31O dissolving 0.0016 gram and a conductivity determina- tion gavel the following numbers:

24. 21.

130.5 4873 132.7 0746

The results arel not very trustworthy, but they indicate that there are only two ions present :

0.1946 gave 0.0522 CO, and 0.0314 H20. 0.0823 ,? 3-6 C.C. N, at 2 8 O and 760 mm. N=4*78. 0’1680 ,, 0.1265 MgS. Hg=64*91.

C = 7.32 ; H= 1.79.

C,H,O,NSHg requires C = 7.82 ; H = 1.63 ; N = 4.56 ; Hg=65*15 per cent.

illethyl Nitromercnytide, MeS*HgNO,.-The method of prepara- There is much

The salt tion is exactly the same as in the preceding case. less tendency towards the formation of the pasty mass. is obtained as a white, crystalline product:

0.1560gave7.0 C.C. N, a t 3 3 O and 760 mm. N=4.79. 0.3400 ,, 0.2660 HgS. Hg=67.44.

CH,O,NSHg requires N = 4.78; H g = 68.25 per cent. Direct estimation of sulphur in the above1 compounds involves

great difficulties. Fusion with potassium nitrate and sodium carbonate invariably gives low results. Thus in the case of ethyl nitromercaptide the percentage1 of sulphur was found to be 7.25, that required by theory being 10.43.

Interaction of the Nitromercaptides and the Alky l Iodides.

Ethyl Nitromercaptide and Ethyl Iodide : Formation of t?be Compoztnd Et2S2,Hg12,EtI.-The nitromercaptide is shaken with an excess of the’ alkyl iodide, when the1 deep red colour of the latter, due t o free iodine dissolved in it, is a t once discharged. The mixture is now digested on a water-bath f o r two to three hours. The completion of the reaction is indicated by the formation of two distinct layers, the lower one being thick and of deeper t int and the upper one much lighter. The heavy bottom layer on cooling deposits yellow prisms and tablets. The lighter liquid is subjected to distillation. The! first fraction consists almost entirely of unchanged ethyl iodide, the succeeding ones of ethyl iodide and nitroethane, and ultimately the temperature1 remains stationary a t 113O, t’he boiling point of nitroethane. The isomeric et8hyI nitrite is also formed, and in some experiments the amount was quantita- tively estimated by the method described in a previous paper

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REACTION WITH THE ALKYL IODIDES. 135

(T., 1915, 107, 1251). The residue in the flask consists of a dark brown liquid of the consistency of treacle. The crude, yellow crystals obtained as above are dissolved in acetone and reprecipi- tated by the addition of water. Care should be taken that the ether be not added in excess, for the first crop-the product of fractional precipitation-is the purest. It has been found throughout the series that. a t least three distinct compounds are simultaneously formed. This is particularly noticeable in the case of the inter- action of methyl iiitromercaptide and ethyl iodide (see below).

The ethyldisulphoniummercuri-iodide, Et,&,HgI,,EtI, as pre- pared above consists of yellow crystals It is insoluble in water or alcohol, and when gently heated in a bulb tube a heavy liquid condenses in the upper stem, a sublimate of iriercuric iodide is deposited, and a charred residue is left in the bulb. When i t is subjected t o dry distillation in a very small flask immersed in an oil-bath, a t first ethyl iodide distils and later a mixture of ethyl iodide and ethyl disulphide, the temperature finally rising t o 1 4 3 O (the boiling point of ethyl disulphide is 15l0), and a, strong, disagreeable, garlic-like odour is perceptible.

Method of Analysis.-As the compounds of the present series have molecular weights ranging from 704 t o 760, the percentage of carbon, which is very low, is scarcely a safe guide in assigning formulae t o them. The estimation of iodine, therefore, was consi- dered preferable. Carius’s method in the presence of mercury and halogens is quite unsatisfactory. After several failures the follow- ing inethod, which is a modification of that adopted €or the estima- tion of mercury in cinnabar, was adopted and gave fairly accurate results.

The substance, contained in a porcelain boat, was placed in a t’ube 1 2 mm. in diameter and a layer of powdered copper 22 cm. in length was placed next to it, the heating being performed in a current of carbon dioxide derived from magnesite. The whole of the iodine is taken up by the copper, forming cuprous iodide. This method has the additional advantage of simultaneously yielding the mercury in the free state. The cuprous iodide when boiled with sodium hydroxide solution reladily gives up its iodine and the sodium iodide in the filtrate is estimated in the usual way. Care should be taken that the weight of the substance to be analysed does not exceed 0.35 gram; otherwise the result is apt to be too low:

melting a t 112O.

0.2385 gave 0.0862 CO, and 0.0510 H,O. 0.2917 ,, 0.2839 AgI ,, 0.082 Hg. 1=52*51; Hg=28.18.

C,H,,I,S,Hg requires C = 9.84 ; H = 2.05 ; I = 52.05 ; H g = 27-32 per cent.

C = 9.86 ; H = 2.38.

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136 RAY : NITROMERCAPTIDES AND THEIR

B'thyl Nitromercaptide atid 2lleth.yl Iodide : Formatiou of t?ie Compound, E t,S,, HgI,, MeI.

A pale yellow, crystalline compound is obtained, which is further purified by dissolving in acetone and precipitating by the addition of ether. It melts sharply a t 86O:

0.2710 * gave 0.2722 AgI and 0.0769 Hg. 1=54.25 ; Hg =28*37. C,€I,,I,S2Hg requires I = 53.06 ; Hg = 27.85 per cent.

Methyl Nitromercaptide and Ethy l Iodide.

It has been already pointed out that a t least three distinct compounds are simultaneously formed, and this could be well followed out in the course of the present reaction. After about three hours' digestion of the components on the water-bath, three distinct layers were recognisable, the bottom layer being viscid and of a golden-yellow colour, the middle layer rather thick and brown, and the upper layer thin and reddish-brown. The upper and middle layers were carefully decanted while still hot, whilst the bottom layer, being viscid, remained adhering t o the flask. The middle portion on cooling solidified to a crystalline, brown mass. It was dissolved in acetone and shaken with ether, when a good crop of the disulphonium compound was precipitated in minute, yellow crystals. The filtrate on evaporation gave a dark brown, semi-crystalline mass of the consistency of treacle. i t was redis- solved in acetone and once more treated with ether, when a fine, cryst'alline powder was deposited and a t the same time a viscid liquid separated out, which on keeping solidified to a mass of crystals ; yellow, minute, oily globules were also found scattered throughout.. These crystals melted a t 63-65O. The filtrate from the second treatment on evaporation left a brown, slightly viscous, crystalline residue. The upper layer, which consisted chiefly of unchanged ethyl iodide, on evaporation left a few drops only of a greenish-yellow oil, the amount of which was too small for purposes of analysis. The bottom golden-yellow liquid on cooling was found to be intermixed with yellow crystals. As i t was evidently a mixture no analysis was undertaken. The largest yield, however, was that of the dis?cZphoniunz derivative, Me@,,HgI,EtI, the melt- ing point of which was 69-71O.

I. The product was simply recrystallised from acetone, bu t not precipitated by ether :

0.3593 gavel 0.3584 AgI and 0.1097 Hg. 1=53.93; Hg=30.54.

++ The substance analysed was not purified by recrystallisation and hence the percentage of iodine is rather high.

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REACTION WITH THE ALKYL IODIDES. 137

11. I n this case the substance was precipitated from acetone

0.2139 gave 0.0617 Hg. Hg=28.85. C,H,,13S,Hg requires I = 54-11 ; Hg = 28.41 per cent.

It has almost invariably been noticed that unless the product is purified as above i t is apt t o be contaminated with a substance containing a higher percentage of mercury.

Analysis of the second crop (m. p. 63-65O) :

0.3084 gave 0.314 AgI and 0.0918 Hg. I=55*02; Bg=29.77. It will thus be evident that the second crop is slightly richer

both in the percentage of mercury and of iodine, although the at,omic ratio of both remailis constant, namely, 1 : 3.

solution by means of ether :

Ethyl Nitronzercaptide and n-Propyl Iodide : Formation of the Compound, E$S,,HgI,, C,H,I.

The components after being heated as above gave a dark brown bottom layer, which yielded dark brown, shining crystals, slightly moist to the touch. These were dissolved in acetone and reprecipi- tated by ether. The colouring matter was thereby removed, and a pale yellolw, crystalline powder was obtained. I ts melting point was not very sharp, lying between 7 5 O and 7 8 O :

0.2744 gave 0.2596 AgI and 0.0715 Hg. I = 51.12; Hg= 26.06. 0.3080 ,, 0’0836 Hg. Hg=27.14.

C7131,13SzHg requires I = 51.07 ; Hg = 26-81 per cent.

illethyl Nitromercaptide and n-Propyl Iodide : Formation of the Compo und, Me,S,,HgIz,C3H,I.

The crystalline mass obtained by treatment of the components as described above W~LG precipitated from acetone solution by ether. I n this manner yellow, mealy crystaIs were obtained, the melting point of which was not very sharp, being between 99O and 102O:

0.3314 gave 0.3204 AgI and 0.0912 Hg. I=52*24; Hg=27*52. C5H1313SLHg requires I = 53.06 ; Hg = 27.86 per cent.

Ethyl Disulphide and Nercuric Nitrite : Formation of the Compound, Et$32,Hg(N0,),,Hg0.

On gradually adding an alcoliolic solution of the disulphide to mercuic nit-rite with brisk stirriiig nitrous fumes are disengaged and a crystalline powder is precipitated, which, under the micro- scope, is found to consist of needles. The salt readily dissolved in hydrochloric acid with copious liberation of nitrous fumes:

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138 SALWAP : STUDIES OK THE OXIDATION OF UNSATURATED

0.2178 gave 0.0552 CO,. 0.1173 ,, 4.8 C.C. W, a t 30° and 760 mm. N=4*43.

C = 6.91.

0.1082 ,, 0.0805 HgS. Hg=64.15. C,If,,O,N,S,Hg, requires C= 7.62 ; N = 4.45 ; Hg = 63.50 per cent.

CHEMICAL LABORATORY, PRESIDENCY COLLEGE,

CALCUTTA. [Received, December 16th, 1915.1

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