Adipic cyclohexene alternative oxidant

Adipic acid historically has been manufactured predominantly from cyclohexane and, to a lesser extent, phenol. During the 1970s and 1980s, however, much research has been directed to alternative feedstocks, especially butadiene and cyclohexene, as dictated by shifts in hydrocarbon markets. All current industrial processes use nitric acid in the final oxidation stage. Growing concern with air quality may exert further pressure for alternative routes as manufacturers seek to avoid NO, abatement costs, a necessary part of processes dial use nitric acid. 

The environmental impact of the cyclohexane oxidation could also be reduced. An alternative is to start from benzene and make a selective hydrogenation to form cyclohexene. Ru-based supported catalysts working in the liquid phase and in the presence of a co-catalysts such as Zn (Asahi Chemical Industry process) are selective in the reaction, with yields up to about 60% [247], but with cyclohexane as the main by-product. Cyclohexene is hydrated in the liquid phase with an MFI zeolite as catalyst at moderate temperature (100-130 °C). This reaction is very selective (>99%). This route was primarily developed for the synthesis of adipic acid, but could be used also to reduce the number of products and separation costs in the production of cyclohexanone. 

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