142 CHALLENGER AND KIPPlNG :XVI. - Organic Derivatives of Silicon. X I I . *Dibenzylethylpropylsilicane and Sulphonic AcidsDerived fi.orn It.By FREDERICK CHALLENGER, B.Sc., and FREDERIC STANLEY KIPPING.WHEN the study of organic derivatives of silicon was commenced byone of us, the principal object in view was the preparation of anoptically active compound containing one asymmetric silicon group.After a short experience of the behaviour of silicon derivatives, theplan which seemed to cffer the best prospect of success was t osyn thesise some asymmetric silico- hydrocarbon, SiR,R,R,R,, whichcould afterwards be sulphonated, and then to resolve the dl-sulphonicacid which would be thus obtained.I n pursuance of this plan, phenylmetbylethylpropylsilicane,SiPhMeEtPr, and phenylbenzylethylpropylsilicane, SiPhEtPr*CH,Ph,were first prepared; but on attempting to sulphonate these compounds,the phenyl group was eliminated as benzene and tertiary silicols wereformed (Kipping, Trans., 1907, 91, 221).I n the case of the phenylbenzyl derivative, this unexpectedbehaviour did not necessitate any change in the original scheme, as itwas found that a sulphonic acid could be obtained from the benzyl-ethylpropylsilicol, CH ,Ph*SiEtPr*OH, which was produced from thesilico-hy drocar bon.Further investigation showed, however, that this sulphonic acid wasderived from the oxide, (SiEtPr-CH,Ph),O, and therefore containedtwo asymmetric silicon groups ; t h i s fact, of course, upset the original* Parts X and XI, Tram, 1909, 95, 302 and 489 respectivelyORGANIC DERIVATIVES OF SILICOX.PART XII, 143plan, but at the same time opened out an alternative one, for if thedl-sulphonic derivative of benzylethylpropylsilicyl oxide which was thusobtained proved to be the dE and not the internally compensated com-pound, it might be resolved into its optically active components. Thesepossibilities were ultimately realised, and in later investigations theresolution of the homologous sulphonic acid derived from benzylethyl-i8obutylsilicyl oxide, (C,H,*SiEt CH,Pb),O, was also accomplished(Kipping, Trans., 1907, 91, 234; Luff and Kipping, Trans., 1908,93, 2090).These acids, which owe their optical activity to the presence of lwoasymmetric silicon groups, are the only active silicon compounds whichso far have been described; they hold this position, not because theoriginal object has been abandoned, but because all attempts to attainit resulted in failure.Thus, during the progress of the experiments referred to above, twoother asymmetric silico-hydrocarbons, namely, benzylmethylethyl-propylsilicane, SiMeEtPr- CH,Ph, and benzylethyl propylbobutyl-silicane, C,H,*SiEtPr*CH,Ph (Kipping, Trans., 1907, 9 1, 717 ;Kipping and Davies, Trans., 1909, 95, 69), were prepared andsulphonated, and many attempts were made to resolve the dl-acidsthus produced, Although, however, the externally compensatedcharacter of the acids could hardly be open to queetion, no definiteevidence of their asymmetry was obtained on fractionally crystallisingtheir salts with active bases.Our knowledge of asymmetric substances is still so incomplete thata reason for these repeated failures can hardly be suggested with anyconfidence.It seemed possible, however, that by preparing a com-pound in which the groups combined with the silicon atom were morewidely different than those in the two acids under discussion, thechances of being able to accomplish a resolution would be increased.Now as most of the readily available alkyl and aryl halogen com-pounds had already been utilised in the preparation of the fourasymmetric silico-hy drocarbons referred to above, the simplest way ofobtaining a new asymmetric sulphonic acid of the desired characterseemed to be to prepare a silico-hydrocarbon containing two benzylgroups and two different alkyl groups, and then to convert this corn-pound into an asymmetric acid by sulphonating one of the benaylgroups.The present paper contains a record of the experiments which haveled to the production of such an acid, namely, dibenzylethylpropyl-silicanemonosulphonic acid, CH,Ph*SiEtPr*CH,*C,H,*SO,H ; thedisulphonic acid, SiEtPr(CH2*C,H,-Su,H)2, derived from the samesilico-hydrocarbon has also been obtained.l)ibenxyZethyl~ropyZs~~cane, SiEtPr(CH,Ph),, was prepared by tli144 CHALLENGER AND KIPPING :interaction of benzylethylpropylsilicyl chloride (Kipping, Trans., 1907,9 1, 722) and magnesium benzyl chloride ; a simpler method, whichwas afterwards adopted, consisted in preparing dibenzylethylsilicylchloride directly from etbylsilicon trichloride and then treating thisproduct with magnesium propyl bromide.The compound thus obtained, like all those silico-hydrocarbonswhich contain a benzyl group, is readily attacked by chlorosulphonicacid at the ordinary temperature, and under suitable conditions ityields a monosulphonic acid, which, however, is invariably accompaniedby a disulphonic acid, It would seem that in both cases only one ofthe possible structural isomerides is formed in appreciable quantities,namely, the para-derivative.The isolation of these two sulphoriic acids was by no means a simpletask, but it was at last accomplished by two methods, namely, by frac-tionally crystallising the mixture of strychnine salts, or of Z-menthyl-amine salt8, prepared from the product of sulphonation.Thedisulphonic acid, which has the symmetrical constitution given above,and is consequently of little interest, has not been examined muchfurther than was necessary for establishing its composition. Itsstrychnine salt is more soluble in water than the salt of the mono-sulphonic acid, and decomposes from about 226'. Its 1-menthylaminesalt is practically insoluble in light petroleum, and melts at 205-20S0.The ammonium, sodium, and barium salts are crystalline.The strychnine and the 1-menthylamine salts of the dkmonosulphonicacid are not resolved during the prolonged course of fractional crystal-lisation which is necessary in separating them from the derivatives ofthe disulphonic acid.The strychnine salt crystallises well, andmelts at 199'.The 1-menthylamine salt,CH,Ph 'SiEt Pro CH,*C,H,*SO,H, C10H21N, 2 H,O,crystallises from moist light petroleum in lustrous plates, and is verysimilar in properties to the corresponding salts of the monosulphonicderivatives of benzylmethylethylpropylsilicane and benzylethylpropyl-isobutylsilicane. This fact was by no means promising, and seemed toindicate that attempts to resolve the new dZ-acid would be just asunsuccessful as those already recorded in the case of the acids justmentioned. Fortunately, however, the great uncertainty of conclusionsbased on analogy in dealing with asymmetric compounds was againillustrated, as, after a few failures, the acid was easily resolved into itsoptically active components.An account of the resolution experiments and of the propertiesof the active acids will be given in the near futureORGANIC DERIVATIVES OF SILICON.PART XII. 145EXPERIMENTAL.Prepurution of Dibenxylet?~ylsiZicyl Chloride, SiEtCl(CH,Ph),.Ethylsilicon trichloride (1 mol., 250 grams), diluted with about sixtimes its volume of dry ether, and magnesium powder (1 atom) areplaced together in a large flask, which is provided with a tap-funnel, astirrer, and a suitable outlet tube.A little benzyl chloride (2-3 c.c.) and a small quantity of anethereal solution of magnesium benzyl chloride (prepared in a test-tube) are now added, and the flask is gently warmed. I n a short timea reaction sets in, accompanied by the separation of magnesiumchloride, and, as soon as this reaction becomes fairly vigorous, the flaskis immersed in melting ice and the stirrer is started.Benzyl chloride(2 mols.) is then run in drop by drop, an operation which occupies abouttwo and a-half hours; when the whole of it has been added, thecontents of the flask are heated under a reflux condenser during threeto four hours. After cooling the product, the granular precipitate ofmagnesium chloride is separated by filtration in absence of moisture(compare Kipping, Trans., 1907, 91, 216) and is washed several timeswith dry ether; on evaporating the combined ethereal filtrate andwashings, there remains a yellow liquid, which fumes in moist air.This liquid is first roughly fractionated under 100 mm.pressurefrom an ordinary distillation flask. Very little passes over below1 6 5 O , but between this temperature and 210' a fairly large fraction iscollected. The thermometer then rises quickly to 2 3 8 O , and anotherlarge fraction distils from 238' to 390'. Distillation may be continuedup to 320°, or even higher, but this fraction has been only superficiallyexamined; the dark green liquid which then remains in the flask issometimes pasty, owing to the presence of magnesium chloride.By systematically fractionating the liquid boiling between 165' and210', using a long-necked flask with a rod-and-disk column, benzyl-ethylsilicon dichloride (Kipping, Trans., 1907, 9 1, 720) is obtained asan oil boiling a t 168-170°/100 mm.The rest of the originaldistillate when similarly fractionated yields a liquid passing overbetween 246' and 251°/70 mm., almost the whole of which, however,boils constantly at 249'. The yield of this product is 40-50 per cent.of the theoretical. The fractions boiling at about 300'/40 mm. containa small quantity of tribenzylsilicyl chloride which separates incrystals on cooling. The formation of this substance is probably dueto the presence of silicon tetrachloride in the ethylsilicon trichloridewhich was employed, and not to the displacement of an ethyl by abenzyl group; from a longer experience of silicon compounds itis concluded that such displacements, at one time thought to bepossible (Robison and Kipping, Trans., 19OS, 93, 440), do not occur.VOL. XCVII.148 CHALLENGER AND KIPPING :The liquid boiling at 249O/70 mm. consists of dibenzylethylsilicylchloride. It was analysed by decomposing it with dilute ammonia andtitrating the neutral solution with silver nitrate ; 1 C.C. = 0.003509gram C1 (Hipping, Trans., 1907, 91, 217) :0.9788 required 35.9 C.C. AgNO,.C1,HI9ClSi requires C1= 12.9 per cent.Dibenxylethglsilicyl chloride is an almost colourless oil, possessing,especially when freshly distilled, a fine bluish-violet fluorescence,which is probably due t o traces of impurity. It has an aromatic,pungent odour, fumes in moist air, and is rapidly decomposed bywater, giving dibenzylethylsilicol, which passes spontaneously intodibenzylethylsilicyl oxide (m. p. 56') when it is kept over sulphuricacid for a week or two.c1= 12.8.DibenxylethylpropyZg~Z~cane, SiEtPr(CH,Ph),.Dibenzylethylsilicyl chloride (1 mol., 170 grams) is mixed with anethereal solution of magnesium propyl bromide (l& mols.), and theether is distilled off.Very little, if any, action takes place until mostof the ether is removed, when a slight separation of magnesium chloro-bromide is observed. The mixture is then heated for about twohours at 140-180°, at the end of which time it is cooled and treatedwith water. The oil which separates is extracted with ether andfractionated under 90 mm. pressure.Distillation begins at about 250°, the thermometer quickly risingt o 262O. Most of the product then passes over between 262' and270°, and only a small quantity of high boiling residue remains in theflask.After further fractionation, pure dibenzylethylpropyhilicane,boiling at 262-265'/90 mm., is obtained. The yield is 70 to 80 percent. of the theoretical :0.1417 gave 0.4166 CO, and 0.1181 H,O.(A)" 0.2244 gave 0.0464 SiO,. Si= 9.7.(B) 0.1202 ,, 0.0253 SiO,. Si=9.89.C,,H,,Si requires C = 80.68 ; H = 9.2 ; Si = 10.05 per cent.The first samples of dibenzylethylpropylsilicane were prepared bythe interaction of benzylethylpropylsilicyl chloride and magnesiumbenzyl chloride. Benzylethylpropylsilicyl chloride ( 1 mol., 20 grams)is added to an ethereal solution of magnesium benzyl chloride(1% mols.), and, as no sign of a reaction occurs at this stage, theether is distilled off and the residue is heated a t about 140' duringone to two hours.The pasty mass of oil and magnesium chlorideis cooled and treated with water. and the oil extracted with ether.When the crude product is distilled under 100 mm. pressure, itC=80.17; H=9.24.* A and B were different preparationsORGANIC DERIVATIVES OF SILICON. PART XII. 147begins to boil at about 210°, and from this temperature to 240'a little dibenzyl passes over; the thermometer then rises rapidlyto 260°, and the silico-hydrocarbon begins to distil. From the liquidcollected between 260' and 280°, dibenzylethylpropylsilicane isobtained by further fractional distillation :0,1948 gave 0.5790 CO, and 0.1628 H,O.0.4567 ,, 0.0945 SiO,. Si = 9.73.C19H,,Si requires C = S0.68 ; H = 9.2 ; Si = 10.05 per cent.Although the yield by this method was very satisfactory, the taskof preparing benzylethylpropylsilicyl chloride, even in an approxi-mately pure condition, is far more troublesome than that ofpreparing pure dibenzylethylsilicyl chloride ; for this reason,practically the whole of the silicane used in this investigation wasobtained by the method described on p.146.DibenzyZeth?/l~opylsiEicane is a colourless liquid with a beautifulviolet fluorescence. It has a pleasant aromatic odour, and is lighterthan water.C= 81.06 ; H = 9.3.It is miscible with most organic solvents.Xulphonation of DibenzyEethylprop~Isilicane.Knowing from previous experience (Kipping, Trans., 1907, 91,223) that sulphuric acid is not a satisfactory sulphonating agentin the case of the silico-hydrocarbons, chlorosulphonic acid was usedin the sulphonation of dibenzylethylpropylsilicnne, and, as it seemedvery likely that both benzyl groups might be attacked, chloro-sulphonic acid (18 mols.), dissolved in a large volume of chloroform,was gradually added to the well-cooled silicon compound, also inchloroform solution.When nearly two-thirds of this solution had beenrun in, a test portion of the product was poured into water and thechloroform mas boiled off; repeating this test at intervals during theaddition of the chlorosulphonic acid, the aqueous solutions of theproduct gradually altered in character. At first they containedvisible drops of unchanged silico-hydrocarbon ; later on, however,they were clear and apparently free from oil while hot, but becamewhite and opaque when cooled, or they were white and opaque whenhot but became quite clear on cooling,Thinking that solubility in water was sufficient evidence thatsulphonation was complete, and as it was very important not touse too large a quantity of chlorosulphonic acid, the addition of thisreagent mas generally stopped as soou as a sample of the productgave a clear solution in hot or cold water.Further investigationshowed, however, that this test was not trustworthy, and that evenwhen the sulphonation product gave a perfectly clear solution inwater (after removiug the chloroform by steam distillation), theL 148 CHALLENGER AND KIPPING :solution might nevertheless contain considerable quantities oi un-changed silico-hydrocarbon; it was also found that when even thetheoretical quantity (1 mol.) of chlorosulphonic acid was employed, aconsiderable quantity of disulphonic acid was formed.In these circumstances various proportions of chlorosulphonic acidwere tried, and the following method of preparation was finallyadopted.A solution of the hydrocarbon (b.p. 262--266O/90 mm.) inchloroform (6 vols.) is cooled in ice, and a solution of chlorosulphonicacid (1% mols.) in chloroform (12 vols.) is added to it drop by dropwhile a rapid stream of dry carbon dioxide is passed through themixture. Hydrogen chloride is evolved almost immediately, and theliquid soon assumes a red colour, which darkens slightly as the.process continues.After keeping the mixture at Oo for a short time, it is poured on ice,and, from the very slowly settling emulsion thus obtained, thechloroform is separated by steam distillation.If the distillation is continued after all the chloroform has beenremoved, oil continues to pass over in small quantities during two orthree hours.This oil is more quickly separated by extracting withether ; it consists almost entirely of unchanged dibenzyletbylpropyl-silicane, but sometimes contains relatively very small quantities ofdibenzylethylsilicyl oxide (m. p. 56O), a fact which seems to show thatthe not very highly purified samples of the silico-hydrocarbon used inthe preparation of the, sulphonic acid contained small quantities ofdibenzylethylsilicol.The almost colourless aqueous solution of the sulphonic acid, whichhas been exhaustively extracted with ether, does not show thepeculiar behaviour referred to above, which, therefore, must beattributed to the presence of the silicane.It is very remarkable,however, that the silicane should dissolve in an aqueous solution ofthe sulphonic acid.Isolation of the Sulpiionic Acids.Many difficulties were met with in attempting to isolate thesulphonic acids produced in the manner described above. Theammonium salt was first prepared and freed from mineral salts by themethod previously used in other cases (Kipping, Trans., 1907, 91,225), but the crude salt was a syrupy or pasty substance, and couldnot be obtained in crystals. Prom the crude ammonium salt, manysalts of organic bases were obtained by precipitation ; of these, thestrychnine salt alone gave crystalline deposits from suitable solvents,and consequently this base was first employed for the purpose in viewORGANIC DERIVATIVES OF SILICON.PART XII. 149I n later experiments, when the properties of the sulphonic acids wereknown, I-menthylamine was used instead of strychnine, but as thereis little to choose between the two methods, they are both described.Method I.-The aqueous solution of the product of sulphonation isneutralised with sodium carbonate and treated with a concert tratedsolution of strychnine hydrochloride. The precipitate which is firstproduced dissolves on stirring, and, after some time, the solutionacquires the appearance of raw white of egg, but on adding morestrychnine hydrochloride a yellow oil is precipitated.'I! he almostclear supernatant liquid is decanted, and the oil is then stirred with alittle more of the solution of strychnine hydrochloride, after which itis extracted five or six times with boiling water and, lastly, with hot8 per cent. aqueous acetone.The remaining oil is then dissolved in alcohol, the solution dilutedwith about half its volume of water, and cooled i n ice ; the crystallinedeposit which is thus obtained is further purified by repeated crystal-lisation from aqueous alcohol, and finally from anhydrous ethyl acetatecontaining a trace of acetone. This product is the strychnine salt ofdl-di benzyleth y lpropylsilicanemonosulphonic acid.The aqueous extracts of the crude strychnine salt, and also thoseobtained with 8 per cent.aqueous acetone, deposit white, ashestos-likeneedles, together with a considerable proportion of oil. Afterseparating the crystals by the aid of the pump, the oil is againextracted twice with hot water, by which means a further quantity ofthe crystalline compound is obtained. The insoluble oily residue thenconsists principally of the strychnine salt of the monosulphonic acid,and is treated accordingly,The salt which is soluble in hot water is dissolved in acetone, whichcontains a very small proportion of water, and the solution is allowedto evaporate spontaneously. The substance which is then deposited,after having been recrystallised from methyl alcohol, consists of thestrychnine salt of dibenzylethylpropylsilicanedisulphonic acid.Nethod 11.-The aqueous solution containing the sodium salts ofthe sulphonic acids is treated with excess of a solution of I-menthyl-nmine hydrochloride, and the precipitated oil is washed with water ;this oil is then repeatedly extracted with boiling light petroleum(b.p. 40-60O). From these extracts the crude Z-menthylsmine saltof dI-dibenzylethylpropylsilicanemonosulphonic acid is deposited inlustrous plates on cooling and stirring well with a little water. Thissalt, however, still contains some Z-menthylamine salt of ihe di-sulphonic acid, from which it is separated by repeated recrystallisationfrom moist light petroleum. I n these operations, petroleum of verylow boiling point gives the best results, because, although the pureZ-menthylamine salt of the disulphonic acid is insoluble even in ligh150 CHALLENGER AND KIPPING :petroleum boiling at 60--80°, it dissolves to a considerable extent inpresence of the salt of the monosulphonic acid.That portion of the precipitated oil which is insoluble in lightpetroleum is dissolved in a small quantity of methyl alcohol, andtreated with ethyl acetate until the well-stirred solution becomesvery slightly turbid.If kept over sulphuric acid, nodular masses ofthe I-menthylamine salt of dibenzylethylpropyIsilicanedisulphonicacid are deposited. From the mother liquors, a further amount of theZ-menthylamine salt of the dl-monosulphonic acid can be obtained byeva.porating them and extracting the residue with light petroleum.St~yclmine dl-Di6enz?lIetl&yt~To~yIs~~~canemo~o~u~~onate,This salt separates from aqueous alcohol or aqueous acetone inhydrated crystals, which melt below 100' and contain 3 moleculesof water:0.9135 of air-dried salt lost 0.0686 H,O.C,,H,,O,N,SSi,3H,O requires H,O = 7.2 per cent.When the hydrated salt is dissolved in ethyl acetate it quicklyseparates again in colourless needles, which still contain water ofcrystallisation and lose weight at 100'.When heated, these do not soften until 160°, but resolidify above thattemperature, and then melt at 199O, the melting point of the anhydroussalt .H,O=7*5.The anhydrous salt was nnnlysed :0,1592 gave 0.4044 CO, and 0.0970 H,O.0,8305 ,, 0.0717 SiO,.Si = 4-06.The anhydrous salt is only very slightly soluble in dry ethylacetate, but dissolves readily in acetone, ethyl or methyl alcohol,chloroform, or toluene. It crystallises in leaflets from benzene, inwhich, however, it is very soluble. Short, stout, prismatic needles areobtained from a mixture of ethyl acetate and acetone. Lightpetroleum and ether have no solvent action.The specific rotation of the anhydrous salt was determined in 98per cent. methyl-alcoholic solution :0.8771, made up to 25 c.c., gave, in a 2-dcm. tube, Q - 0.58'; whenceI n spite of the fact that the isolation of this strychnine salt is onlyaccomplished after a very laborious series of crystallisations fromtwo solvents, the preparation melting at 199' is not a resolutionproduct of the dl-monosulphonic acid, as will be shown later.Conclusive evidence that the salt is really derived from dibenzyl-C = 69.3 ; H = 6.7.C,,H,,O,N,SSi requires C = 68.9 ; H = 6.94 ; Si = 4.09 per cent.[a], -8.26'ORGANIC DERIVATIVES OF SILICON.PART XII. 151ethylpropylsilicanemonosulphonic acid is afforded by the results ofanalyses of several other compounds prepared in the course of thisinvestigation.Strychnine DibenxyZe~hyZ~opyZs~Z~canedisuZphona~e.The pure preparations of this compound, isolated in the manneralready described, consist of a white, gritty powder, which turns brownat 226O and melts completely a t 2314 above which temperature itrapidly decomposes.Under the microscope it is seen to consist of short, rather ill-defined, prismatic needles :0.1894 gave 0.4559 CO, and 0.1170 H20.C = 65.63 ; H= 6.86.0.1780 ,, 0,4293 CO, ,, 0.1098 H,O. C=65*78 ; H=6.86.C,lH70010N,S,Si requires C = 65.8 ; H = 6.35 per cent.Owing to the slight solubility of the salt in 98 per cent. methylalcohol, the specific rotation was determined in 90 per cent. methyl-alcoholic solution :0.6162, made up to 25 c.c., gave, in a 2-dcm. tube, Q - 0.75"; whenceAlthough the strychnine salt of the disulphonic acid might beexpected to have a higher specific rotation than that ([a]D -8.26') ofthe salt of the monosulphonic acid, it seemed probable that the verygreat observed difference might be due to the different proportionsof water in the methyl alcohol employed in determining the twovalues.This conclusion was confirmed by determining the specific rotationof strychnine dibenzylethylpropylsilicanedisulphonate in methylalcohol containing 36 per cent.OF water :0.5298, made lip to 25 c.c., gave, in a 2-dcm. tube, a - 0 . 9 5 O ; whenceThe salt is very sparingly soluble in cold methyl or ethyl alcohol,but "is moderately soluble in the hot solvents, and also in boilingwater ; in ethyl acetate, acetone, benzene, and light petroleum it ispracticaily insoluble, but it dissolves freely in chloroform and inLqueous acetone. The crystals deposited from aqueous solutions meltat about l l O o , and. are doubtless hydrated, as, when dried a t loo",their melting point rises to 226-231'.[a], - 15*21°.[a], -32.4'.l-Jfenthylamine dl-BibenxylethyipropyZsiZicanernonosu1phortccte.This salt crystallises from moist light petroleum in high1 lustrousplates containing 2 molecules of water of crystallisation.Thehydrated salt liquefies at temperatures far below looo, but whe152 CHALLENGER AND KIPPING :kept over sulphuric acid it is completely dehydrated, and then meltsat 99':1.3661 lost 0.0855 H,O. H,O = 6.26.C,,H,70,NSSi,2H,0 requires H,O = 6.55 per cent.The equivalent of the anhydrous salt was determined by boilingwith excess of N/50-sodium carbonate and then titrating with hydro-chloric acid, using litmus as indicator. This method gave the value5 16.4, that required by theory being 5 17.8.The molecular weight of the anhydrous salt was determined by thecryoscopic method in benzene solution :Substance.Solvent . E. M. w.0.795 gram 17 *6 grams 0 -12 1875The calculated value is 517.8.The molecular weight was also determined by the ebullioscopicmethod in methyl-alcoholic solution :Substance.0.089 gram0.207 ,,0.348 ,,0.723 ,,1'006 ,,Solvent. E. M. w.70.0 grams 0.035 3050.075 3320.130 3220.260 3340.360 336These results correspond with those given in benzene and in methyl-alcoholic solutions respectively by the I-menthylamine salt of benzTl-methylethylpropylsilicanesulphonic acid (Ripping, Trans., 1907, 9 1,737), and as the salt is doubtless highly ionised in the latter solvent,the observed values are such as might have been expected.The specific rotation of the anhydrous salt was determined inmethyl-alcoholic solution :0.707, made up to 25 c.c., gave, in a 2-dcm.tube, a - 0.76' ; whenceI-MentTylamine dl-di6enxyletT~yZ23rop~Is~licanenzonosuIp?~onate is in-soluble in water, but dissolves freely in all organic solvents. It maybe recrystallised from aqueous alcohol and from aqueous acetone, butby far the most suitable solvent is petroleum of low boiling point;from this liquid the hydrated salt separates almost completely oncooling, but if the solution is boiled for some time, water is expelled,and the solution of the anhydrous salt does not deposit crystals untilit has been stirred with water.[.ID - 13.4'.Metallic Salts of dl-DibenzyZethyZpl.oioyZsiZicarnemonosuZ~~oitic Acid.The sodium salt was prepared by decomposing the pure Z-menthyl-amine salt with a slight excess of sodium carbonate and distilling offthe liberated base in steam; the very great frothing which occurs iORGANIC DERIVATIVES OF SILICON.PART XII. 153the latter operation may be overcome by dropping alcohol continuouslyinto the liquid.On neutralising the residue with a few drops of acetic acid andevaporating, a soapy mass separates from the cold concentrated solution,but on adding water again and leaving the solution at the ordinarytemperature, the salt is deposited in crystals; it is fairly readilysoluble in cold water, and extremely so in alcohol. It is precipitatedfrom its aqueous solution by sodium hydroxide, carbonate, or acetate.The ammoniuum salt was obtained from the pure strychnine saltas a sticky mass on evaporating its aqueous solution.It is morereadily soluble in water than the sodium salt, and its solution frothsreadily.The barium salt was precipitated in flocculent, oily masses when asolution of the sodium salt was treated with a solution of bariumchloride. It is only sparingly soluble in cold water or alcohol, butdissolves fairly readily in warm aqueous alcohol.I-Mmthylamine Dibenxylethy~ropylsilicanedisulphornote.This salt crystallises from a mixture of ethyl acetate and methylalcohol in nodules, which contain water of crystallisatioo, but which,when anhydrous, melt at 205-208O.The anhydrous salt is readily soluble in ethyl and methylalcohols, but is insoluble in water, acetone, ethyl acetate, lightpetroleum, or benzene..Metallic Salts of the Disulphonic Acid.The ammonium salt of the disulphonic acid was prepared by treatinga warm alcoholic solution of the strychnine salt with excess ofammonium hydroxide; on evaporation of the filtered solution itremained as a yellow solid, which mas purified by recrystallisationfrom a mixture of ethyl acetate and methyl alcohol. It was thusobtained in lustrous plates, readily soluble in the common alcoholsand in cold water, but insoluble in ethyl acetate, acetone, or lightpetroleum.The equivalent of the compound was determined by boiling thesalt with excess of N/5O-sodium carbonate, and then titrating thesolution with acid. The results obtained were 239.4 and 237.4, thetheoretical value being 3 3 8 -4.The sodium salt forms stellate crystals, and is readily soluble inwater, fairly so in alcohol. I n benzene, ethyl acetate, or acetone itis insoluble.The barium salt was precipitated as a granular powder on adding asolution of barium chloride to a neutral solution of the ammoniu154 FRANKLAND AND TWISS: THE INFLUENCE OF VARIOUSsalt.aqueous alcohol :It is sparingly soluble in water, and crystallises well from0.3594 gave 0.1445 BaSO,. Ba = 23-67.C19H,,0,S,SiBa requires Ba = 23.76 per cent.The authors are indebted to the Government Grant Committee ofthe Royal Society for a grant in aid of this research.UNIVERSITY COLLEGE,NOTTINCHAM