Kinetics of decarboxylation of aliphatic acids by cerium(IV) ammonium nitrate

Abstract

The silver(I) catalysed decarboxylation of aliphatic acids by cerium(IV) ammonium nitrate in 2M nitric acid is a first order reaction in [Ce(IV)] and [Ag(I)] and an order < 1 is observed with respect to [RCOOH]. Although there is a first order dependence in [Ce(IV)], the k obs decreased with increasing [Ce(IV)] and there is a linear correlation between k obs −1 and [Ce(IV) m ], where Ce(IV) m is the monomeric cerium(IV) species. Hence monomeric cerium(IV) species are considered to be reactive. The initial presence of Ce(III) retarded the rate and there is a linear correlation between k obs −1 and [Ce(III)]. The k obs is in the increasing order: pivalic > isobutyric > butyric > propionic > acetic acid which is consistent with the relative stability of the respective alkyl radical. The observed rate constant k obs is given by the following equation: k obs= 2K(k+k′[Ag(I)])[RCOOH] 0 1 + K c[H +] + K 1[Ce(III)])(1+2K d[Ce(IV) m]) + K[RCOOH] O which under certain conditions and assumptions is reduced to k obs= 2K(k+k′[Ag(I)])[RCOOH] 0 1 + K c[H +] + K[RCOOH] 0