Structure–reactivity correlations in the aminolysis of aryl dithiomethyl- and dithiophenylacetates with anilines in acetonitrile
作者:Hyuck Keun Oh、Sun Kyung Kim、Hai Whang Lee、Ikchoon Lee
DOI:10.1039/b104295p
日期:——
The kinetics and mechanism of the anilinolysis (XC6H4NH2) of dithio esters, RC(S)SC6H4Z with R = C2H5 and C6H5CH2 are investigated in acetonitrile at 45.0 °C. By application of various structureâreactivity correlations, selectivity parameters ÏX, βX, ÏZ, βZ and ÏXZ are determined. The reactions are predicted to proceed stepwise with rate-limiting expulsion of the ArSâ group. The dithio ester with R = C2H5 exhibits the fastest rate and the largest positive ÏXZ value; this is interpreted to result from the strongest electron donating ability of the ethyl group in the intermediate and a crowded tetrahedral intermediate
and transition state in which the nucleophile (X) and leaving group (Z) are in close proximity due to the bulky C2H5 group. Much faster rates are observed for the thiocarbonyl (CS) rather than carbonyl (CO) esters in the stepwise nucleophilic substitution reactions, which may be ascribed to the lower Ï*CS and Ï*CâLG levels than those of the corresponding antibonding levels in the carbonyl esters. The normal kinetic isotope effects, kH/kDÂ >Â 1.0, involving deuterated anilines suggest concurrent proton transfer with the expulsion of the ArSâ leaving group in a four-center hydrogen bonded transition state.
在 45.0°C 乙腈中研究了二硫酯、RC(S)SC6H4Z(其中 R = C2H5 和 C6H5CH2)苯胺分解 (XC6H4NH2) 的动力学和机理。通过应用各种结构-反应性相关性,可以确定选择性参数δX、δX、δZ、δZ 和δXZ。预计反应将逐步进行,并限速排出 ArS 基团。 R=C2H5的二硫酯表现出最快的速率和最大的正δXZ值;这被解释为中间体中乙基最强的给电子能力和拥挤的四面体中间体的结果
以及过渡态,其中亲核试剂 (X) 和离去基团 (Z) 由于庞大的 C2H5 基团而非常接近。在逐步亲核取代反应中,观察到硫代羰基 (CS) 酯的速率比羰基 (CO) 酯快得多,这可能是由于 α*CS 和 α*C-LG 水平低于相应的反应水平。羰基酯中的反键水平。涉及氘代苯胺的正常动力学同位素效应 kH/kD > 1.0 表明质子转移与四中心氢键过渡态的 ArS- 离去基团的排出同时进行。