Catalytic amounts of Brønsted acidic ionic liquids promoted esterification: Study of acidity–activity relationship

Esterification of aliphatic acids with alcohols was studied using a series of Brønsted acidic ionic liquids as catalysts. The results indicate that five SO3H-functionalized ionic liquids show high catalytic activity and fair reusability even at very low catalyst loadings, while the conventional non-functionalized ionic liquids show poor activity. Hammett method was used to determine the acidity of the ionic liquids and the results were found to be relevant to the catalytic activity observed in the esterification reactions.