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• Series of basic ionic liquids with sterically hindered cations were synthesized. • An ionic liquid catalyzed process for 4-hydroxy-2-butanone synthesis was developed. • The steric hindrance effect on selectivity of product was found and demonstrated. • The catalytic pathways and reaction kinetic were revealed. 4-Hydroxy-2-butanone as important chemical intermediate in the field of both pharmaceutical and food industries is traditionally synthesized from formaldehyde and acetone via aldol reaction with relatively low selectivity due to the heavy side reactions. Herein, series of basic ionic liquids with different sterically hindered cations were prepared for this reaction process. The catalytic performance evaluation results revealed the selectivity of 4-hydroxy-2-butanone could be enhanced with the extension of alkyl chain length substituted in the cation of ionic liquid and increasing number of substituted alkyl group. And the tetraoctyl ammonium hydroxide ([N8,8,8,8]OH) was identified as the optimal ionic liquid catalyst with selectivity of 91.1% toward 4-hydroxy-2-butanone at 40 °C. The kinetic studies indicated the formation of 4-hydroxy-2-butanone was first-order dependent on both acetone and formaldehyde concentrations, with the lowest activation barrier of 49.8 kJ/mol among all steps. [ABSTRACT FROM AUTHOR]