Shape-selective ethylation of biphenyl over a highly dealuminated H-mordenite

Abstract

The shape-selective ethylation of biphenyl over a highly dealuminated mordenite was examined. The ethylation, occurring stepwise, resulted in the formation of ethylbiphenyls (EBP), diethylbiphenyls (DEBP) and tri- and tetraethylbiphenyls (polyethylbiphenyls, PEBP). In the first step, the ethylation was non-shape-selective and gave 17% 4-EBP, with large amounts of the bulkier 2-EBP and 3-EBP isomers. In the second step, the pores of H-mordenite differentiated the diffusion of the EBP isomers, leading to a preferential ethylation of 4-EBP; 4-EBP was consumed rapidly. 3-EBP gradually and 2-EBP did not participate in the further ethylation. Moreover, the transition state of the ethylation of 4-EBP underwent steric restriction by H-mordenite pores, leading to an increase of the selectivity of 4,4′-DEBP up to 30%. The lack of shape selectivity in the first step and the low selectivity for 4,4′-DEBP over HM220 indicate that the space of a H-mordenite pore is too large for highly shape-selective ethylation.