Methanol vinylation mechanism in the KOH/DMSO/CH₃OH/C₂H₂ system

Abstract

ABSTRACT:The reaction mechanism of methanol vinylation with acetylene involving a nondissociated KOH molecule was studied using the MP2/6-311þþG**// HF/6-31þG* approach with the DMSO molecule explicitly included into reaction system. The whole conversion cycle of methanol vinylation including active nucleophile generation, bonding of the latter to the acetylene moiety yielding an intermediate carbanion, final methyl vinyl ether formation, and potassium hydroxide regeneration could be realized in the coordination shell of nondissociated KOH.

Quantum‐chemical models of KOH(KOBut)/DMSO superbasic systems and mechanisms of base‐promoted acetylene reactions

“…Previously, we proposed a general concept of superbase (KOH/DMSO and KOBu t /DMSO) catalysis . According to this concept, the reaction center is represented by a nondissociated molecule of KOH or KOBu t , whose environment can be described by models of various levels of complexity.…”

“…It also neglects the role of alkali metal cation, whose nature can affect both the structure of the reaction products and rates of the transformations . For these reasons, a monosolvate model ( MONO GAS ) comprising a nondissociated alkali molecule and one solvent molecule, which are explicitly taken in the calculation, has been proposed. On one hand, the monosolvate model does not require large computational resources compared to the pentasolvate model.…”

“…On one hand, the monosolvate model does not require large computational resources compared to the pentasolvate model. On the other hand, the monosolvate model demonstrates specific effects of solvation, primarily affecting the loosening of the M‐OH bond in the initial hydroxides and the M‐Nu bond of the resulting DMSO·M + Nu − ·H 2 O complexes . All the above features make the monosolvate model a promising tool for studying the mechanisms of reactions carried out in superbasic media.…”

“…This implies the necessity of the proper orientation of all the reagents, as well as the complete description of the first solvation shell of the cation. When not fulfilled, the monosolvate MONO GAS model (recall that MONO GAS notation means geometry optimization in the gas phase) leads to a different mutual orientation of the reactants in the complexes …”

Two classes of heterocycles—6,8‐dioxabicyclo[3.2.1]octanes and cyclopentenols from the same reagents: A quantum‐chemical comparison of mechanism

“…Previously, we have shown that in the superbase‐catalyzed reactions, the catalyst (KOH/DMSO) can be approximated by the stable complexes of 5DMSO·KOH, in which K + is located in closest pseudooctahedral surrounding formed by DMSO oxygen atoms and hydroxide ions (pentasolvate model) …”