The ethylation of biphenyl over H-mordenite: Reactivities of the intermediates in the catalysis

The ethylation of biphenyl (BP) with ethene was examined over dealuminated H-mordenite (MOR; SiO2/Al2O3 = 206). The ethylation occurred non-shape-selectively, and gave a mixture of ethylbiphenyls (EBPs), diethylbiphenyls (DEBPs), and higher ethylates. The ethylation of BP to EBPs was yielded in the ratio, 2-EBP:3-EBP:4-EBP = 2:2:1 at the initial stages. The reaction occurs under kinetic control. The formation of 4,4′-DEBP was less selective than that of the other isomers; however, the combined selectivity for DEBPs with 4-ethyl groups was higher than 80% during the reaction. 4-EBP was consumed rapidly than the other EBPs in the ethylation of EBPs to DEBPs. Less bulky DEBPs, particularly, 4,4′-DEBP disappeared preferentially compared to the other DEBPs in the ethylation of EBPs to higher ethylates. These results show that the MOR channels are too large for the shape-selective formation of 4-EBP and 4,4′-DEBP by the “restricted transition state selectivity mechanism”.The reactivities of reaction intermediates in the ethylation of BP decreased in the order: 4,4′-DEBP > 4-EBP > BP ≫ 3-EBP ≫ 2-EBP. These three EBP isomers have quite different reactivities for the further ethylation: 4-EBP was preferentially consumed to yield DEBPs with 4-ethyl groups. 3-EBP partly participated in the ethylation to DEBPs, particularly, at high conversion; however, 2-EBP was not ethylated even at the high conversion. Further, 4,4′-DEBP was preferentially ethylated to higher ethylates because it is the most reactive among BP, EBPs, and DEBPs. These high reactivities of 4-EBP and 4,4′-DEBP among their isomers were due to the “reactant selectivity mechanism”.Molecular modeling of the diffusion of the products suggests that the MOR channels are too large for the selective formation of 4,4′-DEBP because all DEBPs can diffuse in the channels. The preferential disappearance of 4-EBP and 4,4′-DEBP is due to the difference of the diffusion in the channels among their isomers. These simulations are corresponding to the experimental results.

Graphical abstractEthylation of biphenyl (BP) was examined over H-mordenite (MOR). The formation of ethylbiphenyls (EBPs) and diethylbiphenyls (DEBPs) was non-shape-selective, although the selectivity for DEBPs with 4-ethyl groups was higher than 80%. 4-EBP, 4,4′-DEBP formed inside the MOR channels are ethylated preferentially to higher ethylates. Figure optionsDownload full-size imageDownload as PowerPoint slide