Nucleophilic Substitution Reactions of 2-Methoxy-3-X-5-nitrothiophenes: Effect of Substituents and Structure-Reactivity Correlations
作者:A. ECHAIEB、W. GABSI、T. BOUBAKER
DOI:10.1002/kin.20863
日期:2014.8
A kinetic study is reported for reactions of 2‐methoxy‐3‐X‐5‐nitrothiophenes 1a–d (X = SO2CH3, CO2CH3, CONH2, H) with piperidine in different solvents at 20°C. It is shown that the reactions take place through a SNAr mechanism with the initial nucleophilic addition step being rate limiting. The satisfactory Hammett correlations (log k1 vs. σ) obtained in the present system confirms that a 3‐X substituent
动力学研究表明,在20°C下,2-甲氧基-3-X-5硝基噻吩1a–d(X = SO 2 CH 3,CO 2 CH 3,CONH 2,H)与哌啶在不同溶剂中的反应。结果表明,反应是通过S N Ar机制进行的,初始亲核加成步骤是速率限制的。令人满意的哈米特相关性(log k 1 vs.σ在本系统中获得的)证实3–X取代基对与5位相同类型的2位起作用。与这些反应相关的二阶速率常数根据关系log k(20°C)= s(E + N)来确定噻吩1a–d的亲电参数E(Angew。Chem。,Int。编英格兰。1994,33,938-957)。发现1a–d的E值覆盖从-21.33到-17.18的范围,从最小的反应性1d到1a,最具反应性的噻吩。有趣的是,已经观察到并讨论了这项工作中确定 的亲电参数E与Hammett的σ常数值之间的线性相关性(r 2 = 0.9910)。另一方面,我们发现,在甲醇中,由甲醇