Berger F, Sauer J. Dimerization of Linear Butenes and Pentenes in an Acidic Zeolite (H-MFI).
Angew Chem Int Ed Engl 2021;
60:3529-3533. [PMID:
33314606 PMCID:
PMC7898720 DOI:
10.1002/anie.202013671]
[Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2020] [Indexed: 11/06/2022]
Abstract
Quantum chemical evidence is produced to show that dimerization of linear butenes and pentenes at zeolitic Brønsted sites in H-MFI yields alkanes featuring cyclohexane rings rather than branched alkenes. The absence of any C=C double bond in the formed cyclic alkane explains the observations that oligomerization stops at the dimer. The calculated reaction enthalpies for the dimerization of 2-pentene in the gas phase are -84 kJ mol-1 for branched alkenes, but -153 and -154 kJ mol-1 for alkyl-cyclopentane and -hexane, respectively. Together with calculated adsorption enthalpies of the dimers, -111 and -127 kJ mol-1 , respectively, this implies surface dimer formation enthalpies of -264 and -281 kJ mol-1 , respectively, in close agreement with the experimental value of -285 kJ mol-1 . In contrast, the predicted enthalpy for formation of branched alkoxides, -198 kJ mol-1 , deviates by 87 kJ mol-1 from experiment. Calculated IR spectra for the Brønsted OH group show the observed conversion of the band at approximately 3000 cm-1 (hydrogen bond with alkene) to a less intense band at approximately 3450-3500 cm-1 (interaction with alkane).
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