Unraveling the reaction route and kinetics of 3-methyl-3-penten-2-one synthesis for synthetic ketone fragrances

BACKGROUND: 3-Methyl-3-penten-2-one (3M3P) is an indispensable raw material for the synthesis of OTNE (octahydrotetramethyl acetophenone), a synthetic ketone fragrance known by commercial trade names such as Iso E Super, which is one of the most important ingredients in perfumes. This work is the first to unravel the reaction route and kinetics for the synthesis of 3M3P via the cross-aldol condensation of acetaldehyde with butanone, catalyzed by the heterogeneous acidic ion exchange resin (NKC-9). RESULTS: An effective method was developed to evaluate this complex reaction system: the reaction routes were determined experimentally from the product structures detected by GC25 MS, and the significance of side reactions were evaluated by the Yoneda group contribution method. The major side reactions are the self-condensation of acetaldehyde (significant even under optimized reaction conditions) and the cross-aldol condensation of acetaldehyde with 3M3P (which could be effectively suppressed at high butanone-acetaldehyde molar ratio). The reaction kinetics was investigated at temperatures of 60-90 °C, catalyst mass fraction of 5-15%, and molar ratio of 5-20. At optimized reaction conditions, the yield of 3M3P was up to 90.85%, 2.4 times higher than that for the classic homogeneous catalysts (yield < 38%). CONCLUSION: Acidic ion exchange resin NKC-9 is a high-selective green catalyst for the cross-aldol condensation of acetaldehyde with butanone. Integrating experimental determination and thermomechanical analysis is an effective method to unravel the main reaction routes for a complex system.