Functionalization of Methylaromatic Hydrocarbons

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Functionalization of dimethylaromatic hydrocarbons such as 1,4-, 1,8-, 2,3- and 2,6-dimethylnaphtalenes, 4,4' -dimethylbiphenyl and p-xylene was investigated in order to aim at highly selective and convenient syntheses of1) bis(bromomethyl)aromatics, 2) bis(hydroxymethyl)aromatics and 3) aromatic dialdehydes.In the synthesis of bis(bromomethyl)aromatics from dimethylaromatic hydrocarbons, visible light irradiation in benzene with N-bromosuccinimide as brominating agent was greatly effective in increasing selectivities of the bis(bromomethyl)aromatics and efficiency of product purification.Bis(hydroxymethyl)aromatics were produced in good yields by refluxing the bis(bromomethyl)aromatics in strongly basic water in the presence of a phase transfer catalyst like triethylbenzylammonium bromide, whose chemical affinity with the bis(bromomethyl)aromatics could be expected to be high.Aromatic dialdehydes were produced in good yields in the tetrabutylammonium periodate oxidation of the bis(bromomethyl)aromatics in dioxane. In order to achieve high selectivities of the dialdehydes, it was necessary to add 2.2 mol equivalents of tetrabutylammonium periodate and a bromine trap like anthracene.The synthetic methods described above are of significance since bis(hydroxymethyl)aromatics and aromatic dialdehydes cannot be synthesized by direct oxidation of dimethylaromatic hydrocarbons.