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本文研究了N-苯基氨基乙酸中苯环间位不同取代基对氨基酸酸碱强度的影响。将按前文方法制得的N-(间-取代苯基)氨基乙酸乙酯用氢氧化钠水溶液皂化,然后用浓盐酸酸化即得N-间-取代苯基氨基乙酸。在0.1M NaClO_4存在下,于15±0.2,25±0.2,35±0.2℃,用配有231型玻璃电极和甘汞电极的PHS-2型酸度计测定了N-(间-取代苯基)氨基乙酸在30%(体积)乙醇中的离解常数。用氨基酸钠盐测定离解常数的方法业已报道。从所测得的氨基酸表观离解常数(表1)可以看出,如同N-(对-取代苯基)氨基乙酸一样,N-(间-硝基苯基)氨基乙酸(m-NO_2PhG)的pK_1值反而比N-(间-氯苯基)氨基乙酸(m-ClPhG)和N-(间-甲氧苯基)氨基乙酸(m-CH_3OPhG)的大。这是不能用诱导效应来解释的。一般说来,氨基酸具有两性离解的性质,存在下列平衡:
In this paper, the effect of different substituents of phenyl ring meta-residues on the acid-base strength of amino acid in N-phenylglycine was studied. The N- (m-substituted phenyl) aminoacetic acid ethyl ester prepared according to the previous method is saponified with aqueous sodium hydroxide and then acidified with concentrated hydrochloric acid to give the N-m-substituted phenylglycine. In the presence of 0.1 M NaClO 4, the amount of N- (m-substituted phenyl) -2-methyl-2-oxo- Dissociation constant of glycine in 30% ethanol by volume. Methods for determining dissociation constants using amino acid sodium salts have been reported. From the measured apparent dissociation constants of amino acids (Table 1), it can be seen that N- (m-nitrophenyl) glycine (m-NO2PhG) The value of pK_1 is instead larger than that of N- (m-ClPhG) and N- (m-methoxyphenyl) glycine (m-CH_3OPhG). This can not be explained by the induction effect. In general, amino acids have the property of amphoteric dissociation, with the following balances: