Amino-acids and peptides. Part XXXV. The effect of solvent on the rates of racemisation and coupling of some acylamino-acid p-nitro-phenyl esters; the base strengths of some amines in organic solvents, and related investigations
作者:A. W. Williams、G. T. Young
DOI:10.1039/p19720001194
日期:——
been measured; the rate for dimethyl sulphoxide is ca. 500 times that for chloroform as solvent. The ratios of the rates of racemisation of (A) and (B) to that of the condensation reaction are relatively low for the solvents tetrahydrofuran, dimethylformamide, and dimethyl sulphoxide, but exceptionally high for chloroform, dichloromethane, acetonitrile, and nitromethane, which are unfavourable solvents
已经确定了三乙胺在九种不同溶剂中的苄氧羰基甘氨酰基-L-苯丙氨酸对硝基苯酯(A)和苄氧羰基-L-苯丙氨酸对硝基苯酯(B)的外消旋化速率。已经测量了酯(B)与甘氨酸乙酯在相同溶剂中的缩合速率。二甲基亚砜的比率约为。以氯仿为溶剂的500倍。对于溶剂四氢呋喃,二甲基甲酰胺和二甲基亚砜而言,(A)和(B)的外消旋速率与缩合反应的比率相对较低,而对于氯仿,二氯甲烷,乙腈和硝基甲烷而言,(A)和(B)的外消旋速率相对较低,而对于在这方面不利的溶剂。胺的性质对酯(A)和(B)以及苯甲酰基-L-亮氨酸p的外消旋化速率的影响报告了乙腈和二甲基亚砜中的-硝基苯酯,并已通过使用2,4-二硝基苯酚作为分光光度指示剂测量了有机溶剂中某些胺的碱强度。甘氨酸乙酯在溶剂中的碱性强度的变化与其亲核性的变化大致平行,该亲核性的变化通过其与酯(B)的反应速率来测量。所述的外消旋化的速率p氯代,2,4-二氯,米硝基- 。苯甲酰基-L-亮氨酸的2