Nucleophilic Reactivities of Hydrazines and Amines: The Futile Search for the α-Effect in Hydrazine Reactivities
作者:Tobias A. Nigst、Anna Antipova、Herbert Mayr
DOI:10.1021/jo301497g
日期:2012.9.21
groups increase the reactivities of the α-position of hydrazines, they decrease the reactivities of the β-position. Despite the 102 times lower reactivities of amines and hydrazines in water than in acetonitrile, the relative reactivities of differently substituted amines and hydrazines are almost identical in the two solvents. In both solvents hydrazine has a reactivity similar to that of methylamine.
胺,肼,酰肼和羟胺与苯甲酸铵离子和醌甲基化物的反应动力学通过紫外可见光谱法,在乙腈和水中,使用常规光谱仪,定流和激光闪光技术进行了研究。从这些反应的二阶速率常数k 2,根据线性自由能关系log k 2=s N(N + E)确定亲核参数N和s N。尽管甲基增加了肼的α-位置的反应性,但它们却降低了β-位置的反应性。尽管10 2胺和肼在水中的反应性比乙腈低两倍,不同取代的胺和肼的相对反应性在两种溶剂中几乎相同。在两种溶剂中,肼的反应性都与甲胺类似。这一观察结果暗示,如果考虑到肼具有两个反应中心,Me取代氨中的一个氢比引入氨基更能增加亲核性。log k 2与相应的平衡常数(log K)或布朗斯台德碱度(p K aH)的关系图未显示相对于烷基胺而言,肼或羟胺的亲核性(α效应)增强。