选择性硝酸氧化合成4-氟-3-甲基苯甲酸

Synthesis of 4-Fluoro-3-Methylbenzoic Acid via Selective Oxidation with Nitric Acid

以间二甲苯为原料,通过硝化反应、硝基还原、重氮化反应、选择性氧化合成了4-氟-3-甲基苯甲酸.研究了在中压条件下,用稀硝酸选择性氧化4-氟间二甲苯,考察了硝酸浓度、反应压力、反应温度及反应时间对反应的影响,同时探讨了反应机理.结果表明,在110℃下,硝酸浓度为30%、反应压力为1.0 MPa时反应2 h,反应的转化率和选择性分别为82.67%和68.02%,4-氟-3-甲基苯甲酸的产率可达56.23%.在氟原子取代基对位的甲基比其邻位的甲基更容易被氧化,氟原子取代基对甲基的吸电子诱导效应和位阻效应是4-氟间二甲苯能选择性氧化的主要原因.

4-fluoro-3-methylbenzoic acid was synthesized from m-xylene via nitration,reduction,diazotization and selective oxidation.An efficient and practical method for the selective oxidation of 4-fluoro-m-xylene to 4-fluoro-3-methylbenzoic acid is proposed with diluted nitric acid in autoclave.The influences of nitric acid concentration,pressure,temperature and time were studied to determine the effect of changes of reaction conditions and the reaction mechanism was explored.The reaction was carried out at 110℃for 2 h with 30%of nitric acid concentration at 1.0 MPa in autoclave.Under theses conditions 82.67%the reatant converted with a selectivity of 68.02%to 4-fluoro-3-methylbenzonic acid,and the yield of 4-fluoro-3-methylbenzonic acid was 56.23%.The methyl group para to the fluoro group was oxidized more easily than the methyl group ortho to the substituent The effect appears to be inductive.