A Greener Alternative for the Synthesis of Methyl Pentenone Using Reusable Cation Exchange Resin

Abstract

Synthesis of methyl pentenone (MPO) using the aldol condensation reaction of methyl ethyl ketone (MEK) and acetaldehyde (AcH) in the presence of mineral acid is a commercially practiced process. The reaction is associated with the formation of a number of side products. We propose an environment-friendly, commercially available heterogeneous cation exchange resin (e.g., Ambelryst-15) catalyst for this reaction and examine its efficacy under optimized conditions. Amberlyst-15 offers better yield as compared to its homogeneous counterpart. The selectivity of the desired product was found to be increasing with the conversion of acetaldehyde, which prompted us to explore the detailed chemistry of the process. The major side products include the oligomers of acetaldehyde of different molecular weights formed by various self- and repeated aldol condensation reactions. The reaction kinetics is studied by performing experiments in batch mode in the presence of Ambelryst-15 (average diameter of 600 μm) at 600 RPM to avoid effects of external mass transfer resistances. The effect of different parameters such as particle size, stirrer speed, temperature, composition, and catalyst loading on the reaction performance is investigated. A detailed kinetic model is proposed based on the Langmuir–Hinshelwood–Hougen–Watson (LHHW) mechanism, which explains the progress of main and side reactions satisfactorily. The proposed route that uses cation exchange resin catalyst holds a potential to make the process more compact and environment-friendly.