Mechanism of alkali metal carbonates catalysing the synthesis of β-hydroxyethyl sulfide with mercaptan and ethylene carbonate
The reaction of β-hydroxyethylation is essential to the current practice of organic chemistry. Here, we proposed a new and green route to synthesize 2-hydroxyethyl n-alkyl sulfide with n-alkyl mercaptan and ethylene carbonate (EC) in the presence of alkali carbonates as catalysts and revealed the mechanism by experiments and theoretical calculations. The reaction reported proceeds rapidly with high yields when it is performed at 120°C and catalytic loading is ~1 mol%. The protocol applies to other mercaptan to synthesize corresponding β-hydroxyethyl sulfide. Density functional theory based calculations show that the energy profile for the reaction pathway. The rate-determining step is the ring-opening of EC. Negatively charged O of alkali carbonates approaches S atom of the −SH under the influence of hydrogen bond. Activated S atom that carries more negative charge serves as a nucleophilic reagent and assists in the ring-opening of EC by reducing the Mayer bond orders of C1−O1 bond in EC. Alkali cations also contribute to the C1−O1 bond cleavage. The energy barrier for ring-opening of EC decreases with the decrease of electronegativity of alkali cations. Subsequent transference of H atom leads to the formation of 2-hydroxyethyl n-alkyl sulfide, the dissociation of CO2 and reduction of K2CO3.
- This article is part of the themed collection: Synthetic methodology in OBC