2,6-二甲氧基苯甲酸的合成

对 2 ,6 二甲氧基苯甲酸的制备方法进行了研究。经三步反应合成 2 ,6 二甲氧基苯甲酸。第一步 :以N ,N 二甲基甲酰胺 (DMF)为溶剂 ,n(间苯二酚 )∶n(碳酸钾 )∶n(二氧化碳 ) =1 0∶0 5∶1 5在 1 3MPa,1 35～ 1 37℃条件下 ,反应 1 6 5h ,使 ,经酸化制得 2 ,6 二羟基苯甲酸 ;第二步 :使n(2 ,6 二羟基苯甲酸 )∶n(硫酸二甲酯 ) =1∶3 ,在碱性条件下反应得到 2 ,6 二甲氧基苯甲酸甲酯 ;第三步 :将上步产物碱催化水解 ,酸化制得 2 ,6 二甲氧基苯甲酸。第一步反应温度较文献值1 50～ 1 80℃低 ,减少了副产物 ;使用锌粉还原脱色、乙醚萃取回收间苯二酚后处理工艺 ,提高了间苯二酚的利用率和产品收率 (2 ,6 二羟基苯甲酸收率为 52 % )。后两步反应是连续进行的 ,烷基化反应温度是 30～ 45℃ ,先滴加w (NaOH) =30 %的水溶液 ,该步反应结束之后 ,补加w(NaOH) =40 %水溶液 ,这两步反应的总收率为 92 6 %。 2 ,6 二甲氧基苯甲酸的总收率为48 1 5 %。化学法测定其质量分数为 99 1 %。

Synthesis of 2,6-Dimethoxybenzoic Acid

Dimethoxybenzoic acid was synthesized by three step reaction.Firstly,2,6 dihydroxybenzoic acid was prepared by the reaction of resorcinol,anhydrous potassium carbonate and carbon dioxide in mole ratio 1 0∶0 5∶1 5 with DMF as solvent at 135-137 ℃ under 1 3 MPa for 16 5 h.Then,under alkaline condition,2,6 dihydroxybenzoic acid and dimethyl sulfate in mole ratio 1∶3 reacted to give methyl 2,6 dimethoxybenzoate.Finally,2,6 dimethoxybenzoic acid was obtained through alkaline hydrolysis of methyl 2,6 dimethoxybenzoate and acidification.In the first step, the reaction temperature was lower than that given in the literature (150-180 ℃),thus reducing the formation of by product.The aftertreatment for recovering resorcinol included zinc dust reduction and decolorization and ether extraction,thus increasing the use ratio of resorcinol and the product yield.The yield of 2,6 dihydroxybenzoic acid was 52% in this step.The latter two steps were carried out continuously.Alkylation was done by dropping w (NaOH)=30% aqueous solution at 30-45 ℃,then hydrolysis was done by adding w (NaOH)=40% aqueous solution at elevated temperature. Total yield of the two steps was 92 6%. The overall yield of 2,6 dimethoxybenzoic acid was 47 8%. Mass fraction of the product is 99 1% as determined by chemical method.