Brønsted acidic ionic liquid as an efficient and recyclable promoter for hydroesterification of olefins catalyzed by a triphenylphosphine–palladium complex

Several Brønsted acidic ionic liquids (BAILs) with different acidic scales were synthesized and employed as acid promoters for the hydroesterification of olefins catalyzed by a triphenylphosphine–palladium complex. The results showed that catalysts with BAIL promoters resulted in moderate to high conversions to the ester product with excellent selectivity, depending on the acidity of BAIL used. The reaction conversion reached a plateau when the catalyst was promoted using BAIL with a Hammett acidity function less than or equal to − 0.11. This catalyst system could be reused several times for the hydroesterification of 1-hexene without a considerable decrease in the catalytic performance.

The hydroesterification of olefins catalyzed by a triphenylphosphine˜palladium complex can be significantly promoted by the Brønsted acidic ionic liquids (BAILs) with SO3H group, producing excellent yield of esters. Figure optionsDownload as PowerPoint slideResearch highlights
► The acidity of Brønsted acidic ionic liquids (BAILs) was influenced by the structures of both anion and cation. In particular, the presence of a SO3H group in the cation of BAIL might be responsible for a higher acidity, which brought about a significant promoting effect on the hydroesterification of olefins catalyzed by a triphenylphosphine-palladium complex. The ester yield attained a plateau when the catalyst was promoted with BAIL that had a Hammett acidity function (H0) less than or equal to -0.11. The catalyst system containing [MIMPs][TsO] BAIL, having a H0 value of -0.11, could be reused several times without considerable loss of activity for the hydroesterification of 1-hexene.