催化加氢合成苯并三氮唑类紫外吸收剂

Synthesis of Benzotriazole Ultraviolet Absorbers via Catalytic Hydrogenation

在催化剂作用和氢气气氛下,经过偶氮化合物加氢还原、脱水环化和加氢脱氧合成苯并三氮唑类紫外吸收剂。相比于化学还原合成方法,催化加氢路线具有原子经济性高、环境友好的特点。通过研究催化加氢合成苯并三氮唑类紫外吸收剂主反应和副反应发生的过程,修改了反应机理,增加了共轭碳碳双键加氢的副反应路线。考察了碱性助剂有效提高目标产物选择性的作用机制。提出了活性氢物种对氮氧化物的还原是引起其开环生成两分子芳胺副产物的主要诱因,三氮唑环与相邻苯环形成的共轭双烯结构的过度加氢生成了四氢副产物。

2-（2＇-hydroxyl-5＇-methylphenyl）-benzotriazole was synthesized via hydrogenation, dehydrationcyclization and hydrodeoxygenation of 2-nitro-（2＇-hydroxyl-5＇-methylphenyl）-azobenzene in the presence of H2 and catalysts. This method is atom-economic and more environmental friendly than traditional chemical synthesis routes. Both main and side reaction processes were studied, and the reaction process was adjusted by adding the hydrogenation of conjugated C=C bonds as another side-reaction path. Moreover, the mechanism of alkaline as the promoter in enhancing selectivity was investigated. It was found that the ring-opening reaction of 2-（2＇-hydroxyl-5＇-methylphenyl）-benzotriazole N-oxide is caused by active hydrogen reduction on N-oxide, and the conjugated double C=C bonds tends to be excessively hydrogenated to generate tetrahydro-byproducts.