酸度对苯基双胍合成反应的影响及其作用机理

Effect of Acidity on Synthesis of Phenylbiguanide and its Mechanism

研究了酸度对苯胺与双氰胺加成反应生成苯基双胍的影响。结果表明,酸度较低时,该反应的速率随酸度增加而显著增加。当pH=2.5时,反应速率达到最大值。酸度继续增加,反应速率逐渐减小。对苯胺和双氰胺的酸碱平衡的计算表明,随酸度的增加,在pH>2.5时,双氰胺的氰基质子化程度增大占主导地位,从而有利于苯胺的亲核加成,使加成反应速率增大;在pH<2.5时,苯胺与质子结合生成苯胺离子占主导地位,因而明显降低了亲核试剂的浓度,使反应速率减小。在pH<3.5时,水分子作为亲核试剂可参与竞争反应,双氰胺发生水解而使主反应的产率降低。通过IR、13C NMR、元素分析测试技术结果证明,副产物为脒基脲。

The effect of acidity on the synthesis of phenylbiguanide from the additive reaction of aniline with dicyandiamide was studied. Under low acidity conditions, the reaction rate was increased with the increase in acidity, and reaches the maximum value at pH = 2. 5. When the acidity was increased, the reaction rate was gradually decreased. The acid-base equilibration of aniline and dicyandiamide was calculated, it shows that when pH 〉 2. 5, the increasing of the concentration of protonated dicyandiamide made the dominant effect and increased the reaction rate. When pH 〈 2.5, the aniline molecule integrated with H^＋ , and the decreasing of nucleophile gave a dominant effect, which decreased the reaction rate. It also shows that dicyandiamide may hydrolyze when pH 〈 3.5, and it is proved by IR, ^13C NMR and elemental analysis that the by product is guanylurea.