Formaldehyde–isobutene Prins condensation over MFI-type zeolites†,Catalysis Science & Technology

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Formaldehyde–isobutene Prins condensation over MFI-type zeolites†
Catalysis Science & Technology ( IF 4.4 ) Pub Date : 2018-10-04 00:00:00 , DOI: 10.1039/c8cy01667d
Efterpi S. Vasiliadou _{1,

2,

3,

4,

5} , Sha Li _{1,

2,

3,

4,

5} , Stavros Caratzoulas _{1,

2,

3,

4,

5} , Raul F. Lobo _{1,

2,

3,

4,

5}

Affiliation

The liquid phase Prins condensation of formaldehyde with butenes on H-ZSM-5 (MFI) zeolite catalysts was investigated showing that reaction rates follow the order isobutene > 1-butene > cis-2-butene. The catalytic rates for medium-pore zeolite H-ZSM-5 were not only a larger than for H-beta, but also selective for 3-methyl-3-buten-1-ol during formaldehyde condensation with isobutene. Isoprene forms, under the optimal reaction conditions, either in a second dehydration step of the unsaturated alcohol, or in a single step over H-ZSM-5 with optimal Si/Al ratio (Si/Al = 40). Mechanistic studies revealed that sequential Prins cyclization and hetero-Diels–Alder reactions of the desired products, forming six carbon species, occur only at slow rates over H-ZSM-5. Using DFT methods it was determined that the reaction follows a two-step mechanism: protonation of formaldehyde and electrophilic attack to the alkene, and deprotonation of the resulting intermediate carbocation. For isobutene and 1-butene, the electrophilic addition is coordinated with the protonation of the formyl group, but for cis-2-butene, it is coordinated with the proton back-donation step. The rate-limiting step switches from electrophilic addition for isobutene to proton elimination for the other two C4 isomers.

中文翻译：

甲醛-异丁烯树脂在MFI型沸石上的缩合†

研究了H-ZSM-5（MFI）沸石催化剂上甲醛与丁烯的液相Prins缩合反应，显示反应速率遵循异丁烯> 1-丁烯>顺式的顺序-2-丁烯。中孔沸石H-ZSM-5的催化速率不仅大于H-β，而且在甲醛与异丁烯缩合过程中对3-甲基-3-丁烯-1-醇具有选择性。在最佳反应条件下，异戊二烯要么在不饱和醇的第二个脱水步骤中形成，要么在具有最佳Si / Al比（Si / Al = 40）的H-ZSM-5上一步形成。机理研究表明，所需产物的顺序Prins环化反应和杂Diels-Alder反应（形成六个碳原子）仅在H-ZSM-5上以较慢的速率发生。使用DFT方法，确定该反应遵循两步机理：甲醛的质子化和对烯烃的亲电攻击，以及所得中间体碳正离子的去质子化。对于异丁烯和1-丁烯，顺式-2-丁烯，它与质子返还步骤协调。限速步骤从对异丁烯的亲电加成转换为对其他两个C4异构体的质子消除。

更新日期：2018-10-04

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