Formation of 2,6-Naphthalenedicarboxylic Acid by the Co-Mn-Br-Catalyzed Autoxidation of 2,6-Diethylnaphthalene in Acetic Acid

Article abstract of DOI:10.1246/bcsj.68.204

In order to elucidate the reaction mechanism and the optimum reaction conditions for the formation of 2,6-naphthalenedicarboxylic acid (NDCA), the Co(OAc)2-Mn(OAc)2-NaBr-catalyzed oxidation of 2,6-diethylnaphthalene by molecular oxygen was carried out in acetic acid.The oxidation of the ethyl groups to carboxyl groups proceeded mainly via groups and partly via 1-hydroxyethyl and 1-acetoxyethyl groups.A synergistic catalytic effect due to Co and Mn acetates was observed not only on the rate of oxidation but also on the selective formation of NDCA.The rate of oxidation was strongly retarded at higher concentrations of the substrate, showing that the naphthalene nucleus terminates the chain reaction step of the oxidation.A high concentration of metal catalyst resulted in an increase of acetoxyethylnaphthoic acid.At the optimum reaction conditions, a nearly 90percent yield of NDCA was obtained along with small amounts of substituted naphthoic and trimellitic acids.The differences in the yield of NDCA from 2,6-dimethyl, 2,6-diethyl, and 2,6-diisopropylnaphthalenes were compared under similar reaction conditions and are discussed.