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

Abstract

BACKGROUND: 3-Methyl-3-penten-2-one (3M3P) is an indispensable raw material used 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 Gas Chromatography Mass Spectrometry (GC-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 to 15%, and molar ratio of 5-20. At optimized reaction conditions, the yield of 3M3P was up to 90.85%, which is 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.

From Batch to Continuous Sustainable Production of 3-Methyl-3-penten-2-one for Synthetic Ketone Fragrances

“…The details and procedure of operating the BSTR can be found in our previous work. 22 The acetaldehyde conversion, 3M3P selectivity, and 3M3P yield are calculated as…”

“…An accurate reaction kinetic model in power law form (as required for RD in Aspen Plus) could not be established for this system of complex reactions, although rigorous reaction kinetics was determined experimentally in our previous publication. 22 A large prediction deviation appears for some of the components; thus, using an inaccurate power law kinetic model would result in incorrect mass balance of the reaction system, which further leads to errors in the balance of the separation system. Therefore, the mass balance of the reaction system was calculated based on the experimental results.…”

“…In our previous work, the heterogeneous acidic ion-exchange resin NKC-9 was successfully used as a catalyst for 3M3P synthesis to solve the problems of equipment corrosion, product loss, and wastewater generation. 22 Although NKC-9 showed better selectivity than the traditional homogeneous inorganic acid catalysts, several problems still need to be solved to improve the sustainability of 3M3P production. First, there is ample room for the further improvement of selectivity.…”

“…Based on the NKC-9 catalyst, our previous work showed that 3M3P is formed by the dehydration of intermediate 3-methyl-4hydroxy-2-pentanone (C6) via the cross-aldol condensation of acetaldehyde with butanone, as shown in Scheme 1. 22 At least five side reactions are possible, the most important ones being the self-condensation of acetaldehyde to form polyaldehydes and the cross-aldol condensation of acetaldehyde with 3M3P to generate the byproduct 3-methyl-2,5heptadien-4-one (C8). In an RDC, these side reactions can be suppressed as follows.…”

“…Ion-exchange resins are typical heterogeneous catalysts that are successfully applied in reactions of etherification, esterification, − and alkylation, showing benign environmental friendliness. In our previous work, the heterogeneous acidic ion-exchange resin NKC-9 was successfully used as a catalyst for 3M3P synthesis to solve the problems of equipment corrosion, product loss, and wastewater generation . Although NKC-9 showed better selectivity than the traditional homogeneous inorganic acid catalysts, several problems still need to be solved to improve the sustainability of 3M3P production.…”