Aminolysis of Y-Substituted Phenyl 2-Thiophenecarboxylates and 2-Furoates: Effect of Modification of Nonleaving Group from 2-Furoyl to 2-Thiophenecarbonyl on Reactivity and Mechanism

Bulletin of the Korean chemical society

Se-Won Min¹  Ik-Hwan Um¹ 

关键词: Aminolysis;    Br©ªnsted-type plot;    Intermediate;    Stepwise mechanism;    Rate-determining step;   

DOI  :  

学科分类：化学（综合）

来源: Korean Chemical Society

【 摘 要 】

Second-order rate constants (kN) have been measured for reactions of Y-substituted phenyl 2-thiophenecarboxylates (6a-h) with morpholine and piperidine in 80 mol % H2O/20 mol % DMSO at 25.0 �? 0.1 oC. The Br┆nsted-type plot for the reactions of 6a-h with morpholine is linear with a lg = ?1.29, indicating that the reactions proceed through a tetrahedral zwitterionic intermediate (T�?). On the other hand, the Br┆nsted-type plot for the reactions of 6a-h with piperidine exhibits a downward curvature, implying that a change in the ratedetermining step occurs on changing the substituent Y in the leaving group. Dissection of kN into microscopic rate constants (i.e., k1 and k2/k?1 ratio) has revealed that k1 is smaller for the reactions of 6a-h than for those of Y-substituted phenyl 2-furoates (5a-h), while the k2/k?1 ratio is almost the same for the reactions of 5a-h and 6a-h. It is also reported that modification of the nonleaving group from the furoyl (5a-h) to the thiophenecarbonyl (6a-h) does not influence pKa^o (defined as the pKa at the center of the Br┆nsted curvature) as well as the k2/k-1 ratio.

【 授权许可】

Unknown