Abstract: 2,4-dimethyl benzoic acid, an intermediate of the acyl phosphine oxide photoinitiator with best performance was synthesized. The reaction mechanism was studied and sodium hypochlorite was used as the substitution of chlorine generally used in the chloroform reaction. The optimal synthesis conditions were found through orthogonal test as follows：the molar ratio of chlorinated acetophenone to sodium hypochlorite 1∶1.3，the amount of the catalyst (benzalkonium bromide solution) 15 mL，reaction time seven hours，reaction temperature 80 ℃. Repeated test showed that the average highest yield was 80%.

摘要： 合成了新型光引发剂酰基膦氧化物的中间体2,4-二甲基苯甲酸，并对其合成反应机理进行了探讨，提出了工艺革新，用次氯酸钠代替传统的氯气进行反应，并通过正交实验分别对两步反应的合成条件进行了优化，得到了最优反应条件，即：物料配比n(α-氯代-2，4-二甲基苯乙酮)∶n（次氯酸钠）为1∶1.3，催化剂的苯扎溴铵的用量为15 mL，反应时间为7 h，反应温度为80 ℃。经重复实验验证，在该最优条件下2,4-二甲基苯甲酸的合成可达到平均收率80%。