The Alkylation of Biphenyl over One-Dimensional Twelve-Membered Ring Zeolites. The Influence of Zeolite Structure and Alkylating Agent on the Selectivity for 4,4′-Dialkylbiphenyl

Abstract

Abstract Alkylation, i.e., isopropylation, s-butylation, and t-butylation, of biphenyl (BP) was examined over one-dimensional twelve-membered (12-MR) zeolites: Mordenite (MOR) and SSZ-24 (AFI) with straight channels, and SSZ-55 (ATS) and SSZ-42 (IFR) with corrugated channels. Types of zeolites and alkylating agents highly influenced the selectivities for dialkylbiphenyl (DABP) isomers. Shape-selective formation of 4,4′-diisopropylbiphenyl (4,4′-DIPB) was observed over MOR and AFI; however, ATS and IFR gave 4,4′-DIPB only in low selectivities at 250 °C: 87% over MOR, 60% over AFI, 20% over ATS, and 30% over IFR. The selectivities for 4,4′-di-s-butylbiphenyl (4,4′-DSBB) in the s-butylation were higher than those for 4,4′-DIPB: 95% over MOR, 85% over AFI, 75% over ATS, and 50% over IFR. The t-butylation afforded selectively 4,4′-di-t-butylbiphenyl (4,4′-DTBB) over the zeolites: 96–97% over MOR and AFI, 90% over ATS, and 80% over IFR. These results in the alkylation indicate the exclusion of 4,4′-DABP from other bulky DABP isomers by steric restriction in zeolite channels is an important key for the high shape-selectivity. Even zeolites with large channels, such as ATS and IFR, can have shape-selective nature if the bulky moieties, such as s-butyl and t-butyl groups, are large enough to differentiate the transition state of the least bulky 4,4′-DABP from those of the other isomers inside their channels. The selectivity for 4,4′-DABP decreased at high temperatures in some alkylations: isopropylation over MOR, and s-butylation and t-butylation over MOR, AFI, and ATS. The decreases are due to the isomerization of 4,4′-DABP at external acid sites, because the channels are not large enough for the isomerization of 4,4′-DABP to bulkier 3,4′-DABP. However, the isopropylation over AFI was accompanied by the isomerization of 4,4′-DIPB at external and internal acid sites, because the channels are large enough for the isomerization of 4,4′-DIPB.