Synthesis of Aromatic Aldehydes and Carboxylic Acids by the Oxidations of Polyaromatic Hydrocarbons

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This study has been carried out aiming at the syntheses of oxygenated products such as aldehydes, ketones, alcohols and carboxylic acids by the oxidations of polyaromatic compounds. Specifically, the photooxidation of 2, 6-dialkylnaphthalenes was extensively studied.Photobromination of side-chain methyl groups on arenes with N-bromosuccinimide was carried out in various solvents at ambient temperatures under nitrogen. Visible light irradiation in benzene solvent was extremely effective in increasing the selectivity of the reaction and the efficiency for product purification. The photobromination of 1, 4-, 1.8-, 2, 3- and 2, 6-dimethyinaphthalenes, 4, 4'dimethylbiphenyl, and p-xylens with 2, 2 mol equivalents of N-bromosuccinimide quantitatively afforded the corresponding bis(bromomethyl)arenes, respectively. The(bromomethyl)-methylarenes were also obtained in good yields in the photobromination reactions of the above dimethylarenes with 1.1 mol equivalents of N-bromosuccinimide. The hydrolysis of 2-bromo-6-methylnaphthalene and 2, 6bis(bromomethyl)naphthalene gave 2-hydroxymethyl-6-methylnaphthalene and 2, 6-bis(hydroxy methyl)naphthalene respectively in good yields.2, 6-Dialkylnaphthalenes were partially and selectively hydrogenated to yield corresponding 2, 6dialkyltetrahydronaphthalenes. The oxidations of these compounds by molecular oxygen with cobalt, manganese and bromide as catalysts gave mixtures of products. The oxidation of phenylcyclohexane has been also studied. It gave methylbenzoate as a major product together with dimethyl esters of glutafic acid and succinic acid.