Electronic and Steric Effects in Regioselective Tritiation of Anilides.

Abstract

Acetanilide, propionanilide, and isobutyranilide were tritiated at the ortho positions with very high regioselectivity by heating with HTO in the presence of RhCl3⋅3H2O in N, Ndimethylformamide (DMF) . In this reaction for pivalanilide the specific activity alone was determined, because attempts to establish the regioselectivity were unsuccessful. The extent of tritium incorporation decreased with increasing bulkiness of the alkyl groups. Only slight tritium was introduced by the same reaction for tri fluoroacetanilide, which would probably be attributed to a strong electron-attracting property of the tri fluoromethyl group. The above findings give support to the previous suggestion that the present isotope exchange reaction proceeds via an initial coor dination of the nitrogen atom of anilides to the rhodium (III) chloride trihydrate catalyst.