Triptycene 1-Carboxylic Acid and Related Compounds. The Decomposition of Ditriptoyl Peroxide

Abstract

Triptycene-1-earboxylic acid (9,10-o-benzenoanthracene-9-carboxylic acid) has been prepared and with it a number of other triptycene derivatives. The acyl peroxide prepared from this acid decomposes in benzene at 80° somewhat faster than benzoyl peroxide. The readiness of formation of the triptycyl free radical under these conditions is indicated by the appearance of about 40 % of triptycene among the products, which is supplanted by a like amount of 1-iodotriptycene when the decomposition is conducted in the presence of iodine. The ability of the triptycyl radical to capture a hydrogen atom from benzene indicates that, as would be expected from previous observations, the stability which characterizes the triphenylmethyl radical is totally lacking in the triptycyl radical. A product results to the extent of about 16% which is believed to arise from a carboxyl inversion reaction like that of Leffler17 which is a polar rearrangement proceeding concurrently with the free radical decomposition. 1-Iodotriptycene, obtainable from the decomposition of the peroxide, appears to be totally inert to displacement reactions in boiling ethyl alcohol as had previously been observed for 1-bromotriptycene. Taken in conjunction with recent results of Doering and of Roberts, this indicates that benzene rings fused on the bridges of bicyclo-[2,2,2joctane have a strongly deactivating influence upon the carbon-bromine bond at position 1, which may be due in part to an electronegative inductive effect and, in part, to a stiffening of the internal bond angles of the cage ring system.2. © 1954, American Chemical Society. All rights reserved.