Substituent effects of halogen atoms on regioselective tritiation of benzanilides

RhCl3 catalyzed regioselective tritiation of benzanilide and para-halobenzanilides with HTO was studied to examine the substituent effects of halogen atoms on the tritium incorporation to the anilino benzene ring. It was established by chemical degradation that the tritiation occurred with virtually 100 % regioselectivity at the o-positions of both the benzene rings in the benzanilides. The p-substituted halogen atoms increased the tritium incorporation ratios of the anilino benzene ring to the benzoyl benzene ring, which in the present hydrogen isotope exchange was considered as an intramolecular reference standard for the tritium incorporation. The average ratios obtained from respective duplicates were 0.386, 1.20, 1.61 and 1.74 in the order of benzanilide, p-F-, p-Cl- and p-Br-benzanilides. On the basis of the results, the reaction mechanism is briefly discussed. (author)