Functionalization of Methylaromatic Hydrocarbons

研究了1，4-，1，8-，2，3-和2，6-二甲基环芳烃、4，4‘-二甲基联苯和对二甲苯等二甲基芳烃的功能化反应，目的是高选择性和简便地合成1)双(溴甲基)芳烃、2)双(羟甲基)芳烃和3)芳香二醛。以N-溴代丁二酰亚胺为溴化剂在苯中进行可见光照射，可以有效地提高双溴甲基芳烃的选择性和产物的提纯效率。双溴甲基芳烃在强碱性水中，在相转移催化剂(如三乙基溴化铵)的催化下回流，可以得到高产率的双羟甲基芳烃，其与双溴甲基芳烃的化学亲和力很高。为了获得较高的二醛选择性，需要加入2.2摩尔当量的四丁基高碘酸铵和类似于菲的溴捕捉剂。由于二甲基芳烃不能直接氧化合成二(羟甲基)芳香族化合物和芳香族二醛，上述合成方法具有重要意义。

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.