Effect of the C substitution on the ketonic decarboxylation of carboxylic acids over m-ZrO: the role of entropy

The kinetics of the ketonic decarboxylation of linear and branched carboxylic acids over m-ZrO 2 as a catalyst has been investigated. The same apparent activation energy is experimentally determined for the ketonic decarboxylation of both linear pentanoic and branched 2-methyl butanoic acids, while the change in entropy for the rate-determining step differs by nearly 50 kJ mol −1 . These results show that the difference in reactivity between linear and branched acids is due to entropic effects, and is related to the probability of finding the reactant molecules adsorbed and activated in a suitable way on the catalyst surface. Entropy effects and not activation energies are responsible for the lower reactivity of branched acids towards ZrO 2 -catalyzed ketonic decarboxylation.