Preparation of C¹⁴-Labelled Acids From C¹⁴o₂ and Aryl Lithium Compounds

A simplified technique was developed for carbonation of Grignard reagents or organolithium compounds, with C 14 O 2 generated from barium carbonate. 3,4-(Dibenzyloxy)-bromobenzene was treated with n-butyl lithium in ether and then with C 14 O 2 to give 3,4-(dibenzyloxy)-benzoic acid-carboxyl-C 14 . The yield was 74% based on barium carbonate. 2,6-Dichlorobenzoic acid-carboxyl-C 14 (yield 77%) and 3,5-dichlorobenzoic acid-carboxyl-C 14 (yield 76%) were prepared from the corresponding dichlorobromobenzenes by a similar sequence of reactions. Attempts to synthesize 2,4- and 2,5-dichlorobenzoic acids by this route gave poor yields of unidentified acids, from which the expected products could not be isolated.