Um Ik-Hwan, Hong Jin-Young, Kim Jung-Joo, Chae Ok-Mi, Bae Sun-Kun
Department of Chemistry, Ewha Womans University, Seoul 120-750, Korea.
J Org Chem. 2003 Jun 27;68(13):5180-5. doi: 10.1021/jo034190i.
Second-order rate constants have been measured for the reaction of 2,4-dinitrophenyl X-substituted benzenesulfonates with a series of primary amines. The nucleophilic substitution reaction proceeds through competitive S-O and C-O bond fission pathways. The S-O bond fission occurs dominantly for reactions with highly basic amines or with substrates having a strong electron-withdrawing group in the sulfonyl moiety. On the other hand, the C-O bond fission occurs considerably for the reactions with low basic amines or with substrates having a strong electron-donating group in the sulfonyl moiety, emphasizing that the regioselectivity is governed by both the amine basicity and the electronic effect of the sulfonyl substituent X. The apparent second-order rate constants for the S-O bond fission have resulted in a nonlinear Brønsted-type plot for the reaction of 2,4-dinitrophenyl benzenesulfonate with 10 different primary amines, suggesting that a change in the rate-determining step occurs upon changing the amine basicity. The microscopic rate constants (k(1) and k(2)/k(-)(1) ratio) associated with the S-O bond fission pathway support the proposed mechanism. The second-order rate constants for the S-O bond fission result in good linear Yukawa-Tsuno plots for the aminolyses of 2,4-dinitrophenyl X-substituted benzenesulfonates. However, the second-order rate constants for the C-O bond fission show no correlation with the electronic nature of the sulfonyl substituent X, indicating that the C-O bond fission proceeds through an S(N)Ar mechanism in which the leaving group departure occurs rapidly after the rate-determining step.
已测定了2,4-二硝基苯基X-取代苯磺酸盐与一系列伯胺反应的二级速率常数。亲核取代反应通过竞争性的S-O和C-O键断裂途径进行。对于与高碱性胺或磺酰基部分具有强吸电子基团的底物的反应，S-O键断裂占主导。另一方面，对于与低碱性胺或磺酰基部分具有强供电子基团的底物的反应，C-O键断裂相当显著，这强调了区域选择性受胺碱性和磺酰基取代基X的电子效应共同控制。2,4-二硝基苯基苯磺酸盐与10种不同伯胺反应的S-O键断裂的表观二级速率常数导致了非线性的布朗斯特型图，表明改变胺碱性时速率决定步骤发生了变化。与S-O键断裂途径相关的微观速率常数（k(1)和k(2)/k(-)(1)比值）支持了所提出的机理。2,4-二硝基苯基X-取代苯磺酸盐氨解反应的S-O键断裂的二级速率常数得到了良好的线性汤川-津野图。然而，C-O键断裂的二级速率常数与磺酰基取代基X的电子性质无关，表明C-O键断裂通过S(N)Ar机理进行，其中离去基团在速率决定步骤之后迅速离去。
