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化学学报
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化学学报 ›› 1959, Vol. 25 ›› Issue (6): 371-376. 上一篇    下一篇

论文

N-苯氨基乙酸与 N-α-萘氨基乙酸的离解常数

陈荣悌, 张蕴文   

  1. 南开大学化学系
  • 投稿日期:1959-07-17 发布日期:2013-06-03

THE DISSOCIATION CONSTANTS OF N-ARYLGLYCINES

CHEN YUN-TI, CHANG YUN-WEN   

  1. Department of Chemistry, Nankai University
  • Received:1959-07-17 Published:2013-06-03

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在25℃时及0.10MNaClO4存在下,N-苯氨基乙酸(ΨG)和N-α-萘氨基乙酸(αNG)在30%(体积)乙醇中的表观离解常数用pH法测定为ΨG:pKCOOH=2.69,pKR2NH2+=4.72;αNG:pKCOOH=2.64,pKR2NH2+=10.83。为便于比较,氨基乙酸(G)的离解常数亦在相同情况下测定为pKCOOH=2.71,pKR2NH2+=9.30。ΨG和αNG的硷性强度相差如此巨大,主要是由于后者有位阻效应之故。ΨG的硷性比G的弱得多,因共轭效应起决定性的作用。改变溶剂的介电常数的结果是使氨基酸的酸硷性均减弱。

The apparent acid dissociation constants of N-phenylglycine and of N-a-naphthylglycine have been determined by pH method at 250C in 30% ethanol solution in the presence of 0.10M sodium perchlorate.That of glycine was also determined under the same conditions for the purpose of comparison.These amino aeids were found to have comparable acid strengths, but their basicity is quite different.N-phenylglycine as a base is much weaker than glycine as expected, while N-a-naphthylglycine shows very strong base strength which is in the same order as that of the N-alkylglycines.This anomaly was explained in terms of steric effect due to the 8-hydrogen atom on the naphthalene ring upon the proton on the ammo group.The lowering of dielectric constant of the solvent led to the decrease of both acid and base strengths of glycine.