tert-Butylation of biphenyl over H-Y and H-beta zeolites; formation and identification of main and by-products

tert-Butylation of biphenyl with tert-butanol has been studied over large-p ore H-Y (15) and H-beta (25) zeolites under liquid phase conditions using c yclohexane as a solvent. The identification of main and by-products has bee n performed by GC-MS analysis. The main products of the alkylation reaction were mono-tert-butylbiphenyls and di- (tert-butyl)biphenyls with preferent ial formation of para- and para,para'-isomers. Higher allcylbiphenyls with alkyl group from C-4 to C'(10) were identified as by-products, These compou nds can be formed by alkylation of biphenyl and/or mono-tert-butylbiphenyls with different alkenes, generated by dehydration of tert-butanol, followed by oligomerisation and disproportionation of the formed isobutylene. A pec uliar effect of the small change in dimensions of micropores of H-beta (ell iptic pores 0.76 nm x 0.64 nm) in comparison with H-Y zeolite (circular por es 0.74 nm) has been reflected by the transalkylation of mono-tert-butylbip henyls to cyclohexylbiphenyls and methylcyclopentylbiphenyls over the more acid H-beta zeolite catalyst, whereas this transalkylation has been not mon itored in the experiments with H-Y zeolite. The occurrence of transalkylati on reactions has been supported by thermodynamic analysis and calculations. (C) 2001 Elsevier Science B.V, All rights reserved.