THE RESOLUTION OF THE KETO-D~LACTONE ETC. 1407 CLIV. -The Resolution of the Keto-dilactone of Benzophenone-2 4 2 4'-tetracarboxyEic A cid. By WILLIAM HOBSON MILLS and CHARLES REYNOLDS NODDER. IT follows from the theory of the tetrahedral distribution of the four valencies of the carbon atom that it spirocyclic compound of the type should exist. in two enantiomorpho,us forms 1408 MILLS AND NODDER RESOLUTION OF KETO-DlLACTONE Previous atteiiipts to oblaiu experimental confirmation of tho inolecular asymmetry of such coiiipounds by resolution into optically active antipodes have however been unsuccessful (Marck-wald Ber. 1906 39 1176; Leuchs and various pupils Ber. 1912, 45 189 2114; 1913 46 2420) although Leuchs and Gieseler were able to obtain bis-6-bromo- y -valerolactone-aa-spirane which contains only two asymmetric carbon atoms in three inactive modifications and they attributed the existence of the third form to the presence of a third centre of asymmetry in the substance, due to its spirocyclic configuration.A spirocyclic compound of the type in question which appeared specially suitable for investigation is the keto-dilactone (I) of benzophenone-2 4 2’ $’-tetracarboxylic acid (11). This compound was prepared by one of us (Proc. Camb. Phil. Soc. 1915 18 149) from di-mxylyl ketone by oxidation to benzo-phenonetetracarboxylic acid and dehydration of the latter by heat-ing with hydrochloric acid. The method of synthesis together with the fact that ths product possesses the correct molecular weight, as we have found by the ebullioscopic method in acetone solution, leaves no doubt that it possesses the structure represented above.After unsuccessful attempts with the commoner alkaloids we have succeeded in resolving this substance into two optically active modifications with specific rotations [aID of approximately k 17O by means of a synthetic optically active base a-phenylethylamine (Hunter and Kipping T. 1903 813 1147; LovBn J . pr. Chem., 1905 [ii] 72 307). Using the d-base the I-acid was obtained, and the d-acid was isolated from the filtrate with the aid of the I-base. The 1-Keto-dilactonic A cid.-The following experiment is described as an example of several which have been carried out with similar results. The keto-dilactonic acid (5.75 grams) was suspended in methyl alcohol (100 c.c.) and a solution of cl-a-phenylethylamine (4.09 grams) having [a]’;;’ 39*64O in methy OF BENZOPHENONE-2 4 2' 4'-TETRACARBOXYLIC ACID.1409 alcohol (12 c.c.) was added drop by drop. The temperature rose from 2 2 O to 2 6 O and a clear solution was obtained after the addi-tion of about two-thirds of the base. After all the base had been introduced dry ether (110 c.c.) was added. The salt rapidly crystallised crystallisation being assisted by rubbing with a glass rod. The crop thus obtained (about 7 grams) was recrystallised from a mixture of methyl alcohol (210 c.c.) and ether (330 c.c.). The recrystallised salt (about 2 grams) was decomposed by treat-ment with hydrochloric acid (D 1-08> and the liberated keto-dilactonic acid carefully washed with water and dried.It was dissolved in niethyl ethyl ketone in which it is more readily soluble than in the other common solvents and polarimetrically examined ; 1.0375 grams in 30 C.C. gave aEo -2.25O (Z=4) whence [a];' - 1 6 . 3 O . Of this product 0.943 gram was combined as before with 0.671 gram of d-base. About 1 gram of salt was obtained which on decomposition gave 0.6127 gram of acid. This was polarimetric-ally examined 0.6127 in 13-1 C.C. gave ug5 - 1-58O ( I = a) whence The I-keto-dilactonic acid was recovered from s o h -tion and analysed (Found C = 59.4 ; H = 2.44. C,,H,O re,quires C=59*99; H=2*37 per cent.). The highest specific rotation which we have observed for the Z-acid in the experiments which we have carried out up to the present is [a];' -17.4O in methyl ethyl ketone solution.The d-Keto-Iactonic d cid.-The filtrate from which as described above the first crop of d-base-Z-acid salt had been deposited gave, on acidification 1.3 grams of an acid which proved to be destro-rotatory; 0.679 gram in 30 C.C. of methyl ethyl ketone gave u$ 0 ~ 7 1 ~ (1=4) whence [a] 7.9'. This acid was then combined with I-a-phenylethylamine having [a] - 38*5O in the following manner. The acid (1.23 grams) was suspended in methyl alcohol (10 c.c.) I-base (0.87 gram) dissolved in methyl alcohol (2 c.c.) was added and the salt precipitated with dry ether (6 c.c.). The acid (0.6585 gram) liberated from this salt was again combined with I-base (0.47 gram). The salt thus obtained gave on decom-position 0.559 gram of acid which was polarimetrically examined ; 0.559 gram in 13.1 C.C.gave a 1.50° (1=2) whence [a] 17'5O. From this acid by repeating the above process 0.426 gram of acid was obtained on which the following observation was made : 0.426 gram in 13.1 C.C. of methyl ethyl ketone gave a 1*1l0, whence [a] 1 7 . 1 O . This acid was then recovered from solution and analysed (Found C = 59.70 ; H = 2.38. C17H,0 requires C = 59.99 ; H = 2.37 per cent.). The optically active forms of the keto-dilactonic acid are con-- 16.9O 1410 ATKINSON HEYCOCK AND POPE THE PREPARATION AND siderably more readily soluble than the racemic form in all solvents examined. When saturated solutions of the d- and Z-modifications in methyl ethyl ketone are mixed an immediate copious precipitate of the racemic form is produced. To show the dependence of the optical activity on the lactonic structure of the compound a solution of the d-acid in approxini-ately 1 per cent. sodium hydrogen carbonate was examined in the polarimeter . The rotation was observed to diminish gradually, sinking to the half value in about twenty-four hours and disappearing completely in about four days. Further experiments on larger quantities of material are in progress in order to extend these observations and particularly to determine the specific rotation of the optically pure acids. One of us (C.R.N.) is indebted to the Department of Scientific and Industrial Research for a grant for which he desires to express his thanks. UNIVERSITY CHEMICAL LABORATORY, CAMBRIDGE. [Received November 2nd 1920.