Study of the decarboxylation mechanism of fluorobenzoic acids by strong N-bases

The kinetics of the decarboxylation reactions of pentafluorobenzoic and tet rafluorobenzoic acids by various N-bases were studied using F-19 NMR spectr oscopy. The rate constants of these reactions are dependent on the structur e of the fluorinated acid and the pK(a) values of the N-bases. Pentafluorob enzoic acid is decarboxylated about two orders of magnitude faster than tet rafluorobenzoic acid. With increasing pK(a) values of the protonated N-base s these reactions became much slower. These results suggested that the rate -determining step of the studied reactions is the attack of the conjugated acid (protonated N-base) on carboxylate anion. Copyright (C) 2001 John Wile y & Sons, Ltd.