ABSORPTION SPECTRA OF SOME SULPHUR COMPOUNDS. 2287CCXL-The Colouy* aid Absoqhoub Spectra qf SomeSulphur Compounds.By JOHN EDWARD PURVIS, HUMPHREY OWEN JONES, andHUBERT SANDERSON TASKER.IN a previous paper (Jones and Tasker, Trans., 1909, 95, 1904) thepreparation and properties of some alkyl dithio-oxalates weredescribed. These esters were found to exhibit a distinct yellowcolour, whilst oxalates and oxalyl chloride are colourless.The dithieoxalates were found to have normal molecular weightsin solution, so that it appears as if their colour had been producedowing to the replacement of oxygen by sulphur.It was therefore decided t o study the absorption spectra of theseand some other sulphur compounds of similar structure in order toascertain, if possible, the cause of the colour of thieoxalates.Thevarious ethyl and phenyl mono-, di- and tri-thiocarbonates wereprepared and examined, as were also the corresponding dithio-oxalates, dithiomalonates, dithiosuccinates, and several other com-pounds containing two atoms of sulphur in the molecule. Theresults are described and discussed in this paper. We are not, atpresent, prepared to suggest a hypothesis to account for the resultsobtained; but those so far recorded for a number of coloured com-pounds of simple structure seem to be of value, and the publicationof them may serve a useful purpose.Each compound was obtained as pure as possible, its absorptionspectrum studied in solution of various concentrations in pure ethylalcohol, and the results are represented by curves in the usual way.A large number of the substances show no band due to selectiveabsorption, and, in these cases, it will be sufficient if the reciprocalsof the wavelengths of the last transmitted lines at a thickness of30 mm., and sometimes also of 2 mm., of solution be recorded; whenthe substance exhibits a band, the position of its head is also noted.The following compounds were examined2288 PURVIS, JONES, AND TASKER: THE COLOUR ANDT hio car6 onat es.Diethyl thiocarbonate, OEt-(TO-SEt, was prepared by the actionof ethyl chlorocarbonate on sodium ethyl mercaptide (Sa.lomon,J .pr. Chem., 1873, [ii], 7 , 255).Diethyl thioncarbomte, OEt-CS-OEt, was prepared as describedby Debus (Annulen, 1850, 75, 136), by the action of heat on ethylxanthate, and was separated from the compound OEt.CS*SEt,which is formed at the same time, by repeated fractional distillation,until the product boiled between 161O and 161'5O.Several analyses established the purity of the substance, whichhad a marked yellow colour.(For example: Found, S=23*9.C,H,,O,S requires S=23*9 per cent.) We were not able to preparethis compound by the action of thiocarbonyl chloride on sodiumor potassium ethoxide.Diphenyl thioncarbonute, OPh-CS*OPh, waa prepared by theaction of thiocarbonyl chloride on aqueous sodium phenoxide(Bergreen, Ber., 1888, 21, 346; Eckenroth and Koch, Ber., 1894,27, 1369).The compound has been described a8 crystallisiag in colourlessplates, but it was found that, after repeated recrystallisation fromalcohol and other solvents, the compound still retained a verydistinct cream colour.The colour was not intense, and smallquantities of the substance might be taken to be colourless, whereasin large quantities the colour is unmistakable.Diethyl dithiocarbonate, SEt*CO*SEt, was prepared by the actionof carbonyl chloride on sodium ethylmercaptide (Salomon, J . p ~ .Chern., 1872, [ii], 6, 443).Diphenyl dithiocmhorutte, p-repared by the action of carbonylchloride on sodium thiophenoxide, crystallises from alcohol in longneedles, melting at 43O, and is quite colourless.Diethyl thionthiocarbonate, OEt-CS-SEt, prepared by the actionof ethyl bromide on potassium xanthate (Salomon, Zoc. cit., p. 445),shows a, distinct yellow colour very similar to that of diethyl thion-carbonate.DiethyZ tm'thiocarb onate, prepared by the action of thiocarbonylchloride on sodium ethylmercaptide, is a deep reddish-orange liquid,boiling at 240°/760 mm.and at 118-119°/10 mm. (Debus,tlnnalen, 1850, 75, 147).Diphenyl trithiocarbortate was prepared by the action of thio-carbonyl chloride on sodium thiophenoxide. It crystallises fromalcohol in short prisms, melting at 43O, and showing a golden-yellow colour lighter than that of the ethyl compound:C,,H,,S requires C = 59.5 ; H = 3-82 per cent.0.1998 gave 0'4335 CO, and 0.0690 q0. C=59*2; H=3*84ABSORPTION SPECTRA OF SOME SULPHUR COMPOUNDS. 2289Diethyl monothio-oxalate, prepared by the action of sodium ethyl-rnercaptide on ethyl chloroglyoxylate (" chloroxalic ether "), asdescribed by Morley and Saint (Trans., 1883, 43, 400), is a liquidboiling at 216O, which shows a very pale yellow colour when examinedin thick layers.The various alkyl dithio-oxalates have already been described(Jones and Tasker, Zoc.cit.).Diethyl dithiornalonate, prepared by the action of malonylchloride on sodium ethylmercaptide, is a colourless liquid, boiling at135O/10 mm. On distilling under atmospheric pressure, this esterappears to undergo decomposition with the formation of derivativesof ethyl mercaptan :0.3421 gave 0.5443 CO, and 0.1894 H,O.C,H,,O,S, requires C = 43-8 ; H = 6.25 per cent.Biphenyl dithiomalonat e, prepared by the action of malonylchloride on phenyl mercaptan or its lead salt, crystallises in long,colourless needles, melting at 94-94'5O :C=43.4; H=6*15.0.2700 gave 0.6151 CO, and 0-1055 H,O.C,,H,,O,S, requires C = 62.5 ; H =4.17 per cent.Diethyl dithiosuccimte, prepared by the action of succinylchloride on sodium ethylmercaptide, is a colourless liquid, boiling at165O/10 mm.The product when first formed was slightlyfluorescent; the fluorescence persisted after distillation, but wasremoved by washing with dilute sodium hydroxide solution :C =46.4 ; H = 6-91.C = 62.1 ; H = 4.34.0.2355 gave 0.4010 CO, and 0.1465 H,O.C8H1,0,S, requires C =46*6 ; H = 6.8 per cent.Diphenyl dithioszcccinat e, prepared by the action of succinylchloride on phenyl mercaptan, crystallises from alcohol in colourlessneedles, melting at 90-90'5O :0.1887 gave 0.4375 CO, and 0.0807 H,O.It may be mentioned that succinyl chloride, which is describedas a liquid, when pure sets to a crystalline solid, melting at 17O.Ethyl ethylthiolacetate, SEt*CH,*CO,Et, prepared from ethylchloroacetate and sodium ethylmercaptide in the cold, is a colourlessoil, boiling a t 187-188O (Claesson, Bull.SOC. chim., 1875, [ii], 23,E thy1 ethyl thiolthioacetate, SEt*CH,*CO*SEt, was prepared bythe action of chloroacetyl chloride on sodium ethylmercaptide ; thereaction was started in a freezing mixture, and completed at 1000.The compound is a colourless liquid, boiling at 101-102°/5 mm.:C,H,,OS, requires S = 39.0 per cent.C = 63.3 ; H = 4-75.C16H140,S, requires C = 63.6 ; H = 4.64 per cent.445).0.2163 gave 0.6095 BaS04. S=38*72290 PURVIS, JONES, AND TASKER: THE COLOUR ANDs-Diethglthiolethae, SEt-CH,*CH,*SEt, prepared by the actionof ethylene dibromida on sodium ethylmercaptide at looo, is acolourless liquid, boiling at 210° (Ewerlof, Ber., 1871, 4, 717;Meyer, Ber., 1886, 19, 3266).Phenyl mercaptan was obtained from Kahlbaum, and thiocarbonylchloride from Schuchardt; both were purified by distillation.Di-phenyl disulphide was prepared and purified by repeated crys-tallisation until quite colourless.We are indebted to Professor Pope for a specimen of pure benzylsulphide.Carbonates.An examination of the absorption curves (Figs. 1 and 2) showsthat well-marked bands are exhibited by diethyl dithio- and trithio-carbonates (MI 1000-solutions), a less pronounced band by diethylthioncarbonate (MI 100-solution) and by diphenyl carbonate anddithiocarbonate ( H / 1000-solutions), and by diphenyl thion- andtrithio-carbonates (M / 10,000-solutions).Table I gives the limits ofgeneral absarption in oscillation frequencies at a thickness of 30 mm.,and, when stated, also at 2 mm.; the position of the head of theabsorption band, when one is present, is also given.TABLE I.Strength ofCO(OEt), (colourless) { 5;:; (2 nmi.)CO(OEt)(SEt) (colonrless) ... { $$: (2 n,m.)CS(OEt), (yellow) { t$;oSubstance. solution..........CO(OPh), 9 2 ......... M/100CO(OPh), ,, ......... 1w/1000CO(OEt)(SEt) ,, ... M/lOOO...............CS(OEt), ,, ..............M/lO,OOOCS(OPh), (cream coloured) ... M/100CS( 0 Ph), ... nq1000CO(SEt), (colonrless) ......... M / l O OCO(SEt), 9 , ......... ll1/10,000CO(SPh), 9 , ......... M/1000CS(OEt)(SEt) (yellow) ......... M/100CS (0 E t)( SEt) , , ......... Jf/lOOOCS(SEt), (orange) ............. Jf/lOOCS(SEt), ,, ............... llf/lO,OOOCS(SPh), (goldei~-yellow). ..... M/100CS (SPh), 2 8 ..,..# ~!/10,000f Jl/lOY Y............... CSCI, (orange-red) -\ M/lOOOHead ofband.3760-328036604058360031603300Limit ofabsorption.4406462035753584343541734254304739803336345335133722340531732801--269530303010350ABSORPTION SPECTRA OF SOME SULPHUR COMPOUNDS. 2291The results given above show that in general the replacement ofan ethyl by a phenyl group causes a shift in the limit of generalabsorption towards the red end of the spectrum.Further, the replacement of oxygen by sulphur in ethyl carbonateand ethyl thioncarbonate causes a very marked increase in theabsorption.The consideration of the cause of the colour and bands exhibitedby these compounds is complicated by the differences which existbetween the ethyl and phenyl esters.Diethyl carbonate showsFIG. 1.Oscillation frcqucncics.31 33 35 37 39 41 43 45merely general absorption but no band, whilst diphenyl carbonateshows a well-defined band (Fig. 2), with its head about 3740,(oscillation frequency) almost identical in position with that ofphenol. This band may therefore be attributed to the presence ofthe phenyl groups, the group O:C<o, having no tendency to producea band.This is the only case in which the modification of thecurve by the substitution of phenyl for ethyl is in the direction ofband formation; usually a band shown by the ethyl ester is partlyand completely obliterated in the phenyl ester, as, for instance, i nthe dithiocarbonate and in the dithio-oxalate, which will be discussed02292 PURVIS, JONES, AND "ASKER: THE COLOUR ANDlater. In the compound CS(OPh),, the band shown by diphenylcarbonate h a been displaced slightly towards the red end of thespectrum, whilst in diphenyl trithiocarbonate the band is so changedthat its form suggests a compromise between the vibration dueto the phenyl groups, and those due to the group S:C<,., whichproduce the band found in diethyl trithiocarbonate.In consequence of these complications introduced by the presenceS*FIG. 2.Oscillai!ion frepmicics.31 33 35 37 39 41 43 45of phenyl groups, the curves of the ethyl esters only can be con-sidered completely comparable with one another.Considering firstthe phemmenon of colour, it is obvious that the mere replacementof one or two oxygen atoms by sulphur does not give rise to colour,since diethyl and diphenyl dithiocarbonates are colourless ; but itis also clear that t>he group :C:S must be regarded as a powerfulchromophore.The following compounds all exhibit colour which may be regardedas caused primarily by the :C:S group : CSCb (orange-red), CS(OEt)AP,SORPTIOX SPECTRA OF SOME SULPHUR COMPOUNDS.2293(yellow), CS(OPh), (cream), thiobenzophenone, CS(Ph), (blue). I nthe case of thiobenzophenone and dimethoxythiobenzophenone, wehave confirmed the results obtained by Gattermann (Ber., 1895, 28,2868) as regards the properties of the compounds and the fact thattheir molecular weights in solution are normal. We have also beenable t o prepare these compounds by the interaction of dry silversulphide and the corresponding chloride. The colour originating inthe :C:S group is very considerably modified by the group to whichit is attached, since in the cases mentioned above it varies fromdeep blue to cream.The difference between the intensity of the colour exhibited bythe compounds CS(OEt), and CS(OPh), is much more marked thanthat between diacetyl and benzil, but the explanation is possiblysimilar to that suggested by Baly and Stewart (Trans., 1906, 89,502) to meet the case of these substances.Until there is more exact knowledge as to the relation betweenthe absorption of light and the structure of organic compounds,i t is not desirable to formulate further hypotheses, but the strikingdifference between the groups :C:S and :C:O may be explained assuggested by Hewitt at the International Congress of AppliedChemistry, 1909, on the following consideration.The attractionbetween carbon and sulphur is less than that between carbon andoxygen, as evidenced by the ease with which the sulphur is replacedby oxygen in the thioketones, thioncarbonates, and thiocarbamides.The mass of the sulphur atom to be held by the smaller force ofattraction is greater, and consequently the period of any vibrationset up would be slower.The bands exhibited by the three compounds CO(SEt),,CS(OEt)(SEt), and CS(SEt), possess a similar shape and persistency,but are shifted successively towards the red end of the spectrum,and become much broader.It is possible that these bands may ariseowing to the formation of linkings between the sulphur atom,which exhibit a greater tendency to become quadrivalent than doesoxygen.0xdat ee.Table I1 gives, for the oxalates and thio-oxalates, the strengthof solution, position of head of band in oscillation frequency, andthe limit of absorption through 30 mm.of solution.Fig. 3 contains the curves for those substances which show bands2294 PURVIS, JONES, AND TASKER: THE COLOUR AND' ~ ' A I ~ J A 11.Strength of Limit ofSubstance. s o h tio 11. Head of hand. ahorption.(CO,Et), (colom.less) . . , . , . , . . M/ 10 __ 3513- (GO&), 9 1 ......... M/lOOO 4423C0,Et 'CO'SEt (almostCO,Et*CO*SEt ,,colourless)(CO'SEt), (yellow).. ..........(CO *SE t), , , ............(CO*S*C,Hv), , , ............(CO *S 'CaH,), , , ............(CO*SPh), ,, ............(CO'SPh), ,, ...........M/100M/lO,OOOMf 10M/lOGOM/10M/lOOOM/lOMf1000M/100iM/lOGORapid extension ofabsorption between3640 and 4000, in-cl icating potential [ band. 1374036403620liapid e s tension ofabsorption between3110 and 3850.3400359327703320246831442484303823803050Table I11 gives similar data, including the limit of absorptionfor a thickness of 2 mm.of solution, for the thiomalonates andother compounds examined, which are all colourless, and none ofwhich show bands.TABLE III.Substance.CH,(CO*SEt), .....................Strengthof solution.J M / l O O O\ M/1000 (2 inni.)M/lOOO .................. CH,(CO*SPh), { M/looo (2 niin.)M/lOOO .................. { M/1000 ( 2 mni.) (CH,*CO *SEt ),Limit ofabsorption.372740633405400538554199M/lOOO 3447 { M/looo (2 mm.) 4005 .................. (CH,*CO'SPh),Nf 1000 4365(CH;SEt), { Jf/1000 (2 mni.) 4603 ........................V/lOOO ..................BEt*CH,-C0,Et { M/1ooo (2 mm.)M/lOOO ............... SEt-CH,*CO*SEt { M/1000 (2 mm.)4354442238304113In all the above cases, the replacement of oxygen by sulphurproduces a very great increase in the absorptive power of thecompound; this is particularly well illustrated by a comparison ofethyl oxalate and monothio-oxalate (table 11) and of the two la&compounds in table 111ABSORPTION SPECTRA OF SOME SULPHUR COMPOUNDS. 2295In the colourless compounds, the replacement of ethyl byphenyl produces a considerable increase in absorption, but this isnot so marked in the coloured compounds, since in the dithio-oxalate the absorptive power of the phenyl compound is inter-mediate between those of the ethyl and propyl compounds.The potential band exhibited by phenyl oxalate is probably dueto the phenyl groups, as in the case of phenyl carbonate, since itsposition is close to that of t'he phenol band.FIG.3.Oscillation frequencies.29 31 33 35 37 89 41 43 45The table and the curves show that both colour and an absorptionband are produced by the structures:R*S*$XO rind Et*S*$XOR-SCO EtO*C:O 'but when R=Ph the band is almost obliterated, it9 in the case ofthe dithiocarbonate. Neither colour nor band is shown by any ofthe other compounds which were examined containing two atomsof sulphur in the molecule. It may therefore be concluded thatthe above structure is associated with the existence of the colourand the band2296 ABSORPTION SPECTRA OF SOME SIIT,PHIJH COM POUNDS.Colour of OcrnZyZ Chloride in Solution.It was observed that, although oxalyl chloride itself and itssolutions in substances like ether, chloroform, and paraffins werequite colourless, yet it forms yellow solutions with phenol, anisole,piperonal, dipentene, and alkyl sulphides.The colour of thesesolutions is similar to, but deeper than, that of the alkyl dithio-oxalates, but the solutions were too unstable to allow of anexamination of their spectra.Oxalyl chloride therefore forms coloured solutions with certainsubstances which also give coloured solutions with tetranitro-methane (Werner, Ber., 1909, 42, 4324). The production of colourfrom oxalyl chloride by admixture with other substances is possiblydue to the formation of additive products with these substances,which, in virtue of the presence of oxygen, sulphur, or ethenoidlinking in the molecule, are capable of forming such additivecompounds.Much further work will be required before definite hypotheses canbe formulated to account for the behaviour of these sulphur com-pounds, and it is hoped that the study may be continued andpossibly extended to some corresponding selenium compounds.The absorption spectra of phenyl mercaptan and benzyl sulphidehave also been examined for comparison with phenol and benzylalcohol.These substances show no band, and the limits of absorp-tion are given in table IV.TABLE IV.Strength of Limit ofSubstance. solution. absorption.M/100 (30 mm.) 3320\ MllOOO (30 mm.) 3460M/100 (30 mm.) 3532........................... C'GHs'SH.....................{ M/lOOO (30 mm.) 3608 (C,H,*UH,),SIt is remarkable that the pronounced band in phenol has beencompletely obliterated by the replacement of oxygen by sulphur,and that tshe three bands in benzyl alcohol (Baly and Collie, Trans.,1905, 87, 1332) have disappeared in benzyl sulphide.The results obtained in the examination of benzyl mercaptan arenot trustworthy on account of the ease with which it is oxidised insolution.The oblitera.tion of bands is possibly to be attributed to thegreater absorptive power of the sulphur compoundsMARSH : DISSOLUTION OF POTASSIUM MERCURI-IODIDE. 2297Cenernl Results.An examination of tjhe absorption spectra of sulphur compoundshas shown that:(1) The replacement of oxygen by sulphur causes a markedincrease in the absorptive power of the compound, and, indeed, oftenresults in the production of colour. An absorption band alsoappears in some cases.(2) Definite absorption bands are shown by sulphur compoundspossessing the following structures, but are not shown by thecorresponding oxygen compounds :0. S* s o -,-yo *s*y:oS:c<@ s:c<"o: o:c<,* s:c<,* *o*c:o *s-c:o(1.) (11.) (111.) (IT. 1 (V.) (VJ. 1Of these, compounds of the type I, 11, IV, and VI are yellow in(3) The group S:C< must be considered a powerful chromophore.(4) I n certain aromatic compounds, such as phenol and benzylalcohol, the replacement of oxygen by sulphur results in obliteratingabsorption bands.(5) It has also been found that, although oxalyl chloride itselfis colourless, it gives yellow solutions with a number of unsaturatedcompounds and compounds containing oxygen or sulphur.colour, and V may be considered as faintly coloured.The expenses of this work were largely defrayed by grants fromthe Government Grant Committee of the Royal Society, and thespectra were examined by means of a spectroscope kindly placed atour disposal by the same body. For both these favours we are gladto make this grateful acknowledgment.UNIVERSITY CHEMICAL LABORATOKP,CAMBRIDGE