Pyridinolyses of 2,4-Dinitrophenyl Phenyl Carbonate and 2,4-Dinitrophenyl Benzoate: Effect of Nonleaving Group on Reactivity and Mechanism¢Ó

Bulletin of the Korean chemical society

Min Ji Son¹  Ik Hwan Um¹  Song I Kim¹  Kalsoom Akhtar¹ 

关键词: Br©ªnsted-type plot;    2;    4-Dinitrophenyl phenyl carbonate;    Pyridinolysis;    Rate-determining step;    Stepwise mechanism;   

DOI  :  

学科分类：化学（综合）

来源: Korean Chemical Society

【 摘 要 】

Second-order rate constants (k_N) have been measured for reactions of 2,4-dinitrophenyl phenyl carbonate (2) with a series of pyridines in 80 mol % H₂O/20 mol % DMSO at 25.0 �? 0.1 ^oC, and compared with the k_N values reported for the corresponding reactions of 2,4-dinitrophenyl benzoate (1) to investigate the effect of nonleaving group on reactivity and mechanism. The reactions of 2 result in larger kN values than those of 1. The Br┆nsted-type plot for the reactions of 2 exhibits a downward curvature (i.e., �?₂ = 0.84 and �?₁ = 0.16), which is typical for reactions reported to proceed through a stepwise mechanism with a change in rate-determining step. The pK_a at the center of the Br┆nsted curvature, defined as pK_a^o, has been found to be 8.5 and 9.5 for the reactions of 2 and 1, respectively. Dissection of k_N into the microscopic rate constants (e.g., k₁ and k₂/k_-1 ratio) has revealed that the reactions of 2 result in larger k₁ values than those of 1, indicating that PhO behaves as a stronger electron-withdrawing group than Ph. However, the k₂/k_-1 ratio has been found to be independent of the electronic nature of Ph and PhO.

【 授权许可】

Unknown