TRANS-CTCLOPENTANE-1 : 2-DICARBOXYJAIC ACID. 2639CCXLVI1.-Besolution of trans-cycloPentune-I : 2-di-carboxylic Acid.By LEONARD JAMES GOLDS WORTHY and WILLIAM HENRYPERKIN, jun.IN accordance with the theory of Le Be1 and van't Hoff, manyof the dicarboxylic acids of the cyclic hydrocarbons should becapable of resolution into optically active modifications. Hitherto,only two acids of this type have been investigated in this respect,and the first to be resolved was tmns-hexahydrophthalic acid :CO,H H\//\$!H,*CH2*YCH,*CH;CH CO,lfI n 1899, Werner and Conrad (Bey., 32, 3050) showed that thisexternally compensated acid may be resolved into its activemodifications by the fractional crystallisation of the quinine salts,and the active acids were found t o have a,, + 1 5 - 2 O and --18*5Orespectively.These invetigators also showed that, whilst the e s -ternally compensated acid is almost insoluble iii water and melt2640 GOLDSWORTHY AND PERKIN : RESOLUTION OFat 215O, the d- and I-modifications melt a t 179--183*, and axemuch more soluble; again, the anhydrides of the active acids melta t 164O, or considerably higher than that of the dl-acid, whichmelts at 140O. Furthermore, the conversion of the acids intotheir anhydrides is attended by a reversal and a t the same timeconsiderable increase of the rotation, since the 6-acid (a, + 18.2O)yields an anhydride with a, - 76-7O; the) dimethyl est'ers have thesame sign as their acids and the rotations a, + 28*6O and - 39*Gorespectively. At a later date (Ber., 1905, 38, 31121, Buchnerand von der Heide investigated tl.ans-cyclopropane-I : 2-dicarb-oxylic acid,and showed that this acid can be resolved into its active com-ponents by the fractional crystallisation of the salts with brucine,quinine, or cinchonidine.The active acids melt a t 175O, that is,a t the sme temperature as the &-acid, and have a, +84-5O; allattempts to prepare the anhydrides of these acids have been un-successful, since they distil unchanged and are not acted on byacetyl chloride.Some years ago, a series of experiments was commenced inthe Laboratories of ManChester University by one of us in con-junction with Mr. H. D. Gardner with the object of effectingthe resolution of tmns-cy dopentane-1: 2-dicarboxylic acid,(Perkin, T., 1887, 51, 244), but the investigation was notcompleted.We have now taken up the subject again and find that resolutionmay be readily and completely brought about with the aid ofbrucine.When the dl-acid is combined with bruciiie and the mixed saltsare recrystallised from water, the salt of the d-acid separates firstand is readily obtained pure by.repeated recrystallisation. TheZ-acid may then be recovered from the mother liquors in themanner described on p. 2643. The observed rotations of the d-and7-modifications were a,, + 87.6 and - 85.9 respectively, and thoseof the corresponding ethyl esters, a, 4- 70*31° and - G9.76O. Thed- and I-modifications of cyclopentane-1 : 2-dicarboxylic acid melta t 1 8 2 O or 2 1 O higher than the melting point of the dl-modifica-tion (m.p. 1 6 0 O ) . For the sake of ready comparison, the rotationsand melting points of the trma-cyclopropane-, -pentsane-, and-hexane-1 : 2-dicarboxylic acids are appeiiclecl in tabular form 'I'ltANS-CYCLOYENTANE-1 : 2-DICARROXPIJC ACID. 2641&I. p. of M. p. ofal,. a],. d- and I- inactive(1-acid. l-acid. ncids. acid.fr/c I LS -cycZoPropane -trL~rLs-cycloPentane-t mns -cycloHexane -Z : 2-dicarhoxylic acid . . . . . ... . + 84.9 ' 84.5" 175" 175"1 : 2-dicarboxylic acid .. . . . . . . . -t 87.6" -- 85.9" 181" 1 tic)"1 : 2-dicarboxylic acid ......... +18.2' -18.5" 178-183' 215'It would be interesting t o fill up the gap between trans-cyclo-propane-1 : 2-dicarboxylic acid and the corresponding cyclopentane-dicarboxylic acid by the resolution of t~a.ns-cyclobutane-1 : 2-di-carboxylic acid,?€I,* H*CO,HCH,*CH'CO,Hbut, unfortunately, the preparation of this acid (T., 1894, 65, 585)in quantity sufficient for resolution is most troublesome and,although experiments with this object have been commenced, wehave not yet been able to separate the active modifications in apure state.EXPERIMENTAL.d-t rans-cycloPen tan e- 1 : 2-dicar b o x ylic A cid.The dl-t~~ns-cyclopentane-1 : 2-dicarboxylic acid employed inthese experiments was prepared by the method described by Perkin(T., 1887, 51, 240; compare T., 1894, 75, 586).The pure acid,in quantities of 15 grams, dissolved in hot water, was mechanicallystirred, and brucine (90 grains) gradually added, when the alkaloidreadily dissolved.The excess of brucine was filtered off, wellwashed with hot water, and the filtrate and washings were con-centrated on the water-bath until crystals just commeiiced t o formon the surface. When the liquid was cooled and vigorously stirred,a copious crystallisation took place, and the whole became semi-solid ; the crystals were then collected and repeatedly recrystallisedfrom hot water. During this operation, the progress of the separa-tion of the brucine salt of the d-acid from that of the Z-modi-fication was followed with the polarimeter, and the table givenbelow shows that the separation is nearly complete after six crys-tallisations, since the difference between the rotation of this cropand of that obtained as the result of the twelfth crystallisationis very small.Weight ofNo.of subst,ance. 0 b served SpeciGccrystallisation. Gram. rotation. rotation.1st crop 0.8250 - l-Q!P -32.1'3rd 9 9 0.4566 - 1.14" - 25.0'6th ), 0.5050 - l*liiO - 22-8012th )) 0.2612 - 0.51" - 19.92642 GOLDSWOHTIIY AND PERKIN : RESOLUTION OPA specimen of tlie pure bruciiie salt was subsequently preparedby adding excess of bruciiie to the hot dilute aqueous solution ofthe pure d-acid (see below), and, after filtering, the solution wasallowed to crystallise slowly over sulphuric acid, when large,brilliant, tabular crystals separated. As these crystals efflorescein a vacuum desiccator, they were dried by exposure t o air, andthen analysed :0.1314 gavel 0.2782 CO, and 0.0859 H,O. C=57*7; H=7.3.0.5079 ,, 32.6 C.C.N, at 19.8O and 753 mm. N=5-1.2C23H2s0,hT,,C7H,,0~,9H,0 requires C = 57.4 ; H = 7.2 ; N = 5- 1per cent.That the salt has this composition was confirmed by the factthat 0.2316 gram, heated for one hour a t 125O, lost 0.0336 H,O,whereas the calculated loss for 9H,O is 0.0339 gram.I n order t o obtain the pure d-acid, the brucine salt from thetwelfth crystallisation was dissolved in hot water, the brucineprecipitated by ammonia and, after filtering and washing, thesolution of the ammonium salt was concentrated and acidifiedwith hydrochloric acid when, on cooling, the d-acid separatedin plates, and melted a t 178-180°. After completely decolorisingwith tlie aid of animal charcoal, and twice crystallising fromwater, the acid melted a t 18lo, and 0.1752 dissolved in water(20 c.c.) gave, in a 2-dcm.tube, a rotation of +1*535O, whencea, +87*6O. On titration, 0.1778 required 0.0898 NaOH forneutralisation, whereas this amount of an acid, C,H,(CO,H),,should neutralise 0.0900 NaOHThe d-ethyl ester, C,H,(CO,Et),, was prepared by boiling thed-acid with five times its weight of 10 per cent. alcoholic sulphuricacid for six hours; water was then added, the ester extracted withether, and, after washing with water and dilute sodium carbonate,the ethereal solution was dried, evaporated, and the ester distilledunder diminished pressure.It boiled constantly at 170°/100 mm., and 0.2596, dissolved inacetone (20 c.c.), gave, in a 2-dcm.tube, a rotation of + 1*825O,whence a, +70*3lo.The d-Anilide, C,H,(CO*NH.C,H,),.-In order to prepare thisderivative, the d-acid was heated with thionyl chloride in a sealedtube in boiling water for an hour, the clear liquid evaporated onthe water-bath, and the residual acid chloride dissolved in benzeneand mixed with excess of aniline. The benzene was removed byevaporation, the residue stirred with dilute hydrochloric acid, andthe crystalline precipitate collected and recrystallised twice froTRANS-CYCLOPENTANE-1 : 2-DICAKBOXYLIC ACID. 2643iuetihyl alcohol, in which itt is sparingly soluble, separating as avoluminous mass of needles melting a t 245-247O (uncorr.) :0.2756 gave 21.7 C.C. N, a t 18.4O and 762 mrn.N=9*1.C,,H,,02N, requires N= 9.1 per cent.0.1708, dissolved in acetone (20 c.c.), gave, in a 2-dcni. tube,the rotation + 1*880°, whence a, + 110*lo.Attempts which were made with the object of preparing theanhydride of the d-tram-acid were not successful and the resultsobtained seem t o throw some doubt on the existence of thisanhydride. Since, however, trans-cyclohexane-1 : 2-dicarboxylic acid(trans-hexahydrophthalic acid) yields an anhydride without diffi-culty (Baeyer, Annale?z, 1890, 258, 179), there is every reasonto suppose that the anhydride of tram-cyclopentane-1 : 2-dicarb-oxylic acid should also be capable of existence, but i t is doubtfulwhether the substance described by Haworth and Perkin (T., 1894,65. 985) can be accepted as this anhydride.I-trans-cycloPentane-1 : 2-dicarboxylic A cid.I n order to obtain this acid, the mother liquors from the firstsix crystallisations of the Srucine salt of the dl-acid (p. 2641) wereconcentrated until crystals began to appear on the surface of thebrown liquid. The salt, which separated in quantity on cooling,was dissolved in hot water, the solution decolorised with animalcharcoal, and the crude Z-acid isolated in the manner describedin the case of the d-acidThis acid is readily obtained pure simply by recrystallising fourtimes from water, i t then melted sharply at 180-181°, and 0.2363,dissolved in water (20 c.c.), gave, in a 2-dcm. tube, a rotatiqn of- 2*03O, whence a, - 85*9O, On titration, 0.3110 required 0.1568NaOH for neutralisation, whereas this amount of an acid,C,H,(CO,H),, should neutrslise 0.1575 NaOH.The 1-ethyl ester, C,H,(CO,Et),, obtained in the manner describedin detail in the case of the ester of the d-acid, distilled a t170°/100 mm., and 0.3326, dissolved in acetone (20 c.c.), gave,in a 2-dcm. tube, a rotation of -2.3Z0, whence u, -69-76O.THE UNIVERSITY MUSETJM,OXFORD