Performance of combined use of chlorosilanes and AlCl 3 in the carboxylation of toluene with CO 2

Carboxylation of toluene with CO 2 for the production of p‐toluic acid was shown to be promoted by the addition of Me 2 PhSiCl, Ph 2 SiCl 2 , Ph 3 SiH, or Ph 3 SiCl into the AlCl 3 activated system, and the reaction activity was in the increasing order of Ph 2 SiCl 2  < Me 2 PhSiCl < Ph 3 SiH < Ph 3 SiCl. The spectrum of IR indicated that CO 2 could be effectively activated by AlCl 3 or Ph 3 SiCl independently. DFT calculation was carried out to estimate the electrophilic potentials of the chlorine bridged AlCl 3 ···chlorosilane complex in the form of the APT atomic charges of Si and Al. The much higher activity of Ph 3 Si‐Cl···AlCl 3 over AlCl 3 ‐AlCl 3 was considered due to its higher valences of Si and Al which are +2.107 and +1.833 compared with the +1.814 of Al in the latter. The mechanism of CO 2 activation under the action of double Lewis acid sites of Si and Al and the subsequent carboxylation of toluene was consequently proposed. © 2016 American Institute of Chemical Engineers AIChE J , 63: 185–191, 2017