ACTION OF PHOSPHORUS HALIDES AND THIONYL CHLORIDE ON BENZILIC ACID*

By S. A. SETLUR AND V. V. NADKARNY (From the Department ofChemistry, St. Xavier's College, Bombay)

Received July 5, 1940 (Communicated by Dr. B. Sanjiva Rao, M.A., Ph.D.) KLINGER AND STANDKE4 who studied the reaction of phosphorus penta­ chloride on benzilic acid mention the reported preparation of benzilic acid chloride by Cahours as a liquid of B. P. 270 0 C. and state that on investiga­ tion they found that the liquid was only a mixture of benzophenone and benzophenone chloride. By the action of five moles of phosphorus penta­ chloride on a mole of benzilic acid they obtained a liquid which was assumed by them to contain benzilic acid chloride Ph"'c(OH in addition to Ph/ "COCl Cl c-chlorodiphenylacetic acid chloride Ph"c/ They however gave no Ph / "COCl evidence for the existence of the former, although the existence of the latter Ph. ,NHPh was moved by them by preparing its di-anilido derivative )c( . • Ph '-CONHPh Bickell reports that with five moles of phosphorus pentachloride at 120-30° e-chlorodiphenylacetic acid chloride is formed. The reaction between the acid and phosphorus oxychloride was investi­ gated by Bistrzycki and Herbst." The main product of the reaction was reported to be a-chlorodiphenylacetic acid. It is clear, therefore, that there is no definite information in chemical literature regarding the action of phosphorus pentachloride on benzilic acid. The present authors have studied the action of phosphorus halides on ben­ zilic acid in connection with other synthetic work. In the Klinger and Standke's method (loc. cit.) of preparing benzilic acid amide the yield ob­ tained is found to be small when one mole of phosphorus pentachloride is made to react with a mole of benzilic acid. This low yield is probably con­ nected with the formation of the chloro-acid in preference to the acid chloride. Since a comparatively mild chlorinating agent like phosphorus oxy-chloride

* This paper formed part of the thesis on which Mr. S. A. Setlur was declared eligible to receive the M.Sc. Degree of the University of Bombay. 266 Action ofPhosphorus Halides & Thiollyl Chloride on Benzilie Acid 267 reacts only with the alcoholic -OH in the molecule leaving the carboxylic -OH unattacked, it is highly improbable that phosphorus pentachloride should first attack the carboxylic -OH. Definite experimental evidence obtained by us indicates that phosphorus pentachloride does attack the alcoholic -OH group first. For, we have isolated c-chlorodiphenylacetic acid as the main product of the reaction in benzene solution of one mole of phosphorus pentachloride, on one mole of benzilic acid. Phosphorus oxy-chloride separates as a lower layer and is removed. It is found that no benzilic acid amide is obtained when the reaction product is treated with solid ammonium carbonate, thus indicating that no acid chloride is formed. With excess of phosphorus pentachloride, a-chlorodiphenylacetic acid chloride is formed as evidenced by the fact that the product of reaction, on treatment with ammonium carbonate, gives benzilic acid amide in good yield. In this case the C-CI linkage is rapidly hydrolysed to C-OH by the water present, while the -COCl is changed to -CONH;1 by ammonia. This is independently Confirmed by the fact that the chloro acid, on treatment with ammonium carbonate and ammonia, gives almost quantitatively benzilic Ph NH acid and only a very small yield of a-aminodiphenylacetic acid >c< 2 Ph/ "COOH The action of phosphorus trichloride on benzilic acid, which has not been studied hitherto, also gives a-chlorodiphenylacetic acid. Hans Meyer" obtained benzophenone by the action of thionyl chloride on benzilic acid. By the action of thionyl chloride on benzilic acid in carbon tetrachloride solution at room temperature for a number of days, Stolle" obtained a-chlorodiphenylacetic acid. But on refluxing benzilic acid (one mole) with thionyl chloride (six moles) in carbon tetrachloride solution he obtained «-chlorodiphenylacetic acid anyhydride. Our work confirms generally Stolle's results. We have found that a practically theoretical yield of the chloro-acid can be obtained by the action of about 1·2 moles of thionyl chloride on dry benzilic acid at room tempera­ ture, if care is taken to avoid loss of thionyl chloride. Experimental Action offive moles of phosphorus pentachloride on a mole of benzilic add.-IO g. of dry benzilic acid and 50 g. of phosphorus pentachloride are ground together in a dry mortar. Within a short time a vigorous reaction starts at some point in the reaction mixture and soon spreads throughout the mixture developing heat and a copious evolution of hydrochloric acid fumes: A3 F 268 S. A. Setlur and V. V. Nadkarny

A liquid is formed, and the unreacted crystals of phosphoiUS pentachloride remain at the bottom. The supernatant liquid is transferred to a large beaker containing 60 g. of solid ammonium carbonate. The pestle is washed with a little benzene and the washings are added to the ammonium carbonate. When the vigorous reaction subsides, a little concentrated ammonia is added and the mixture is warmed on the water-bath. It is then cooled and filtered. The solid is recrystallised from choloroform. The yield is 7 g. of benzilic acid amide m.p. 1530 C. On acidification the filtrate does not deposit any benzilic acid. Action ofone mole ofphosphoruspentachloride on a mole ofbenzilic acid.­ 2·2 g. of dry benzilic acid and 2 g. of phosphorus pentachloride, both dis­ solved in benzene, are mixed together and kept overnight at room temperature in a filter flask. The greater portion of benzene is evaporated at room tem­ perature by applying suction to the flask when the liquid is found to separate into two layers. The lower layer is of phosphorus oxychloride. The large crystals that separate from the concentrated benzene solution are found, on recrystallisation, to have a m.p. of 1200 (decomp.). Yield is 1·5 g. Action of phosphorus trichloride on benzilic acid.-2 g. of dry benzilic acid and 2 C.c. of phosphorus trichloride are mixed in a filter flask, which is then slightly warmed and kept corked overnight. Excess of phosphorus tri­ chloride is removed by applying suction at room temperature. The residue is extracted with dry benzene. From the benzene solution crystals having m.p. 1200 (decomp.) and identical with a-chlorodiphenylacetic acid separate. Yield is 1·5 g. Action of thionyl chloride on benzilic add.-Dry powdered benzilic acid (10 g.) is taken in a conical flask fitted with a cork carrying a tube bent twice at right angles and terminating in a calcium chloride tube. Thionyl chloride (3 c.c.) is added and the mixture shaken and kept overnight. Large crystals are formed and on washing with a little benzene-petrol mixture give m.p. 119-200 (decomp.). Yield is 10 g. Summary Klinger and Standke's claim of having prepared benzilic acid chloride by the action of phosphorus pentachloride on benzilic acid is untenable. Even comparatively mild chlorinating agents like phosphorus trichloride, phosphorus oxychloride and thionyl chloride react with benzilic acid replac­ ing the alcoholic -OR by -Cl and giving a-chlorodiphenylacetic acid. The same product is obtained in benzene solution at room temperature by the action of one mole of phosphorus pentachloride on a mole of benzilic acid. Action ofPhosphorus Halides &; ThioJtyl Chloride OIl. BenziNe Acid 269 Excess of phosphorus pentachloride then reacts with the carboxylic group giving «-chlorodiphenylacetic acid chloride. Thionyl chloride reacts with benzilic acid at room temperature giving a good yield of «-chlorodiphenylacetic acid. The authors wish to thank Prof. R. N. Bhagvat, M.A., B.SC., Director, Department of Chemistry, St. Xavier's College, Bombay, for his kind interest throughout the work.

REFERENCES I. Bickel .. Berichte, 1889,22, 1538. 2. Bistrzycki and Herbst .. Ibid., 1903,36, 145. 3. Hans Meyer .. Monatshefte fiir Chemie, 1901,22,791. 4. Klinger and Standke .. Berichte, 1889,22, 1211. 5. Stolle .. Ibid., 1910,43,2471.