Hydronium-Ion-Catalyzed Elimination Pathways of Substituted Cyclohexanols in Zeolite H-ZSM5

作者：Hintermeier Peter H; Eckstein Sebastian; Mei Donghai; Olarte Mariefel V; Camaioni Donald M; Barath Eszter^*; Lercher Johannes A^*

来源：ACS Catalysis, 2017, 7(11): 7822-7829.

DOI：10.1021/acscata1.7b01582

• Dehydration
• Elimination reactions
• Zeolite
• Heterogeneous catalysis
• Homogeneous catalysis

Hydronium ions in the pores of zeolite H-ZSM5 show high catalytic activity in the elimination of water from cyclohexanol in aqueous phase. Substitution induces subtle changes in rates and reaction pathways, which are concluded to be related to steric effects. Exploring the reaction pathways of 2-, 3-, and 4-methylcyclohexanol (2-McyOH, 3-McyOH, and 4McyOH), 2- and 4-ethylcyclohexanol (2-EcyOH and 4-EcyOH), 2-n-propylcyclohexanol (2-PcyOH), and cyclohexanol (CyOH) it is shown that the E2 character increases with closer positioning of the alkyl and hydroxyl groups. Thus, 4-McyOH dehydration proceeds via an El-type elimination, while cis-2-McyOH preferentially reacts via an E2 pathway. The entropy of activation decreased with increasing alkyl chain length (ca. 20 J mol(-1) KT-1 per CH2 unit) for 2-substituted alcohols, which is concluded to result from constraints influencing the configurational entropy of the transition states.

• 出版日期2017-11