4B acid was synthesized from p-nitrotoluene by reduction and sulfonation in this work. The optimum reaction conditions, which sulfofication temperature is 175℃, mole ratio of sulfuric acid and p-toluidine is 1.1∶1,mass ratio of activity carbon and p-nitrotoluene is 1∶20, and producing water of reaction process is separated, have been found by the orthogonal test .Under the optimum conditions, the yield of sulfofication can reach 93.7%.The total yield and the purity of 4B acid can reach 83.3% and 98.0%,respectively. The structure and purity were confirmed by element analysis and color spectrum.%以对硝基甲苯为原料经还原、磺化两步反应合成4B酸。通过正交试验确定最佳工艺条件为磺化温度175℃，硫酸与对甲苯胺的摩尔比为1.1∶1,活性炭与对硝基甲苯的质量比为1∶20。在优化条件下，磺化收率达到93.7%,4B酸的总收率达到83.3%,产品纯度为98%。产品经元素分析、高效液相色谱分析证实了它的结构和纯度。
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