An unsymmetrical behavior of reactant units in the Kolbe–Schmitt reaction

Abstract

Paths of the Kolbe–Schmitt reaction were investigated by the use of RB3LYP/6-311(+)G(d,p) density functional theory calculations. In a monomer model composed of C6H5O−, Na+ and CO2 affording sodium salicylate [C6H4(OH)CO2−Na+], a proton-shift step (Z Naturforsch 57a:812, 2002) was found to have an unrealistically large activation energy. In consideration of the phenol volatilization in the Kolbe’s experiment and the need of the linearity of the proton-transfer path, a dimer model was constructed. Again, a mutual proton-transfer step has a large activation energy. Alternatively, in a dimer model, a transfer path where the phenoxide ion in one monomer acts as a proton acceptor was found to have a reasonable energy. Addition of one more sodium ion leads to the significant lowering of activation energies. Thus, in the dimer, two monomers behave differently (A + A → A + B); one is as if it were a catalyst.