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
作者:Yoshihiro Sugi、Hiroyoshi Maekawa、Akira Ito、Chikako Ozawa、Tomoko Shibata、Akihiro Niimi、Chihara Asaoka、Kenichi Komura、Yoshihiro Kubota、Jae-Youl Lee、Jong-Ho Kim、Gon Seo
DOI:10.1246/bcsj.80.2232
日期:2007.11.15
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.
研究了联苯(BP)在一维十二元(12-MR)沸石上的烷基化,即异丙基化、叔丁基化和叔丁基化:这些沸石包括具有直槽的 Mordenite (MOR) 和 SSZ-24 (AFI),以及具有波纹槽的 SSZ-55 (ATS) 和 SSZ-42 (IFR)。沸石和烷化剂的类型对二烷基联苯(DABP)异构体的选择性有很大影响。在 MOR 和 AFI 上观察到了 4,4′-二异丙基联苯(4,4′-DIPB)的形状选择性形成;然而,ATS 和 IFR 在 250 °C 时只能以较低的选择性生成 4,4′-DIPB:对 MOR 的选择率为 87%,对 AFI 的选择率为 60%,对 ATS 的选择率为 20%,对 IFR 的选择率为 30%。4,4′-di-s-butylbiphenyl (4,4′-DSBB) 在 s-butylation 中的选择性高于 4,4′-DIPB 的选择性:对 MOR 的选择性为 95%,对 AFI 的选择性为 85%,对 ATS 的选择性为 75%,对 IFR 的选择性为 50%。在 t-丁基化反应中,沸石可选择性地生成 4,4′-二对丁基联苯(4,4′-DTBB):比 MOR 和 AFI 高 96-97%,比 ATS 高 90%,比 IFR 高 80%。这些烷基化结果表明,沸石通道中的立体限制将 4,4′-DABP 与其他笨重的 DABP 异构体排除在外,是实现高形状选择性的重要关键。即使是具有大通道的沸石,如 ATS 和 IFR,如果其通道内的笨重分子(如 s-丁基和 t-丁基)足够大,足以将最不笨重的 4,4′-DABP 的过渡态与其他异构体的过渡态区分开来,也会具有形状选择性。在某些烷基化反应中,4,4′-DABP 的选择性在高温下会降低:异丙基化反应优于 MOR,s-丁基化反应和 t-丁基化反应优于 MOR、AFI 和 ATS。温度降低的原因是 4,4′-DABP 在外部酸位点发生了异构化,因为通道不够大,无法将 4,4′-DABP 异构化为体积更大的 3,4′-DABP 。然而,AFI 上的异丙基化伴随着 4,4′-DIPB 在外部和内部酸位点的异构化,因为通道足够大,可以使 4,4′-DIPB 异构化。