微波辅助合成3,4-二氨基苯甲酸

SYNTHESIS OF 3,4-DIAMINOBENZOIC ACID UNDER MICROWAVE IRRADIATION

以对氨基苯甲酸为原料,在微波辐射下经乙酰化、硝化、水解及还原反应制得3,4-二氨基苯甲酸(Ⅰ),总收率为67．6%(未用微波辐射时为40．7%),反应时间由6 h缩短为1 h,并探讨了合成条件。在n(p- H2NC6H4COOH):n(Ac2O)=1:2,微波功率800 w的条件下,回流5 min,对乙酰胺基苯甲酸(Ⅱ)的收率为93．8%;n(Ⅱ):n(Ac2O)=1:2,使用过量乙酸酐,在冰水浴中滴完浓硝酸后,在微波功率800 W,回流3 min后,4-乙酰氨基-3-硝基苯甲酸(Ⅲ)的收率为85．3%;在微波功率800 W条件下,Ⅲ与过量的w(KOH)= 50%乙醇溶液,回流5 min,3-硝基-4-氨基苯甲酸(Ⅳ)的收率为93．1%;在Ⅳ的乙醇溶液中,在回流温度下滴加w[(NH4)2S]=9%硫化铵溶液,然后,在微波功率800 W条件下,回流5 min,可得90．8%的目标产物Ⅰ。用IR、1H NMR对化合物Ⅰ～Ⅳ进行了表征。

3,4-diaminobenzoic acid （Ⅰ） was synthesized under microwave irradiation from 4-aminobenzoic acid via acetylating with Ac2O, nitration with AcONO2, hydrolysis and then reduction with （NH4）2S in ethanol with an overall yield of 67.6% （40.7% under no microwave irradiation）. Reaction time was shortened from 6 h to 1 h under microwave irradiation. Optimal conditions were obtained： n（p-H2NC6H4COOH） ： n（Ac2O） = 1：2, under microwave irradiation in 100 mA （ or 800 W）, refluxing 5 min, p-acetylaminobenzoic acid （Ⅱ） was prepared with 93.8% yield; n（ Ⅱ ） ： n （Ac2O）=1：2, in excess acetyl anhydride after adding concentrated nitric acid in ice-water bath, re fluxing 3 min and under microwave irradiation in high grade, 3-nitro-4-acetamidobenzoic acid （Ⅲ） was obtained in 85.3% yield; m in excess w（KOH）= 50%in ethanol solution, refluxing 5 min, and under microwave irradiation in high grade, 3-nitro-4-aminobenzoic acid （Ⅳ） was obtained in 93.1% yield; Ⅳ in ethanol solution being reduced by ammonium sulfide of w[（NH4）2S] = 9% under refluxing for 5 min, Ⅰ was obtained in 90.8% yield under microwave irradiation in high grade. Compounds Ⅰ-Ⅳwere characterized by IR and ^1H NMR.