Kinetics and Mechanism of the Aminolysis of 4-Methylphenyl and 4-Chlorophenyl 2,4-Dinitrophenyl Carbonates in Aqueous Ethanol
作者:Enrique A. Castro、Paola Campodonico、Alejandra Toro、José G. Santos
DOI:10.1021/jo034385q
日期:2003.7.1
concerted, although it is also possible that both mechanisms (stepwise and concerted) operate simultaneously. By comparison of the reactions under investigation between them and with similar aminolyses, the following conclusions can be drawn: (i) ClPDNPC is more reactive than MPDNPC toward the two amine series. (ii) The change of water to aqueous ethanol destabilizes a zwitterionic tetrahedral intermediate
苯胺与4-甲基苯基和4-氯苯基2,4-二硝基苯基碳酸酯(分别为MPDNPC和ClPDNPC)和后者的底物与仲脂环族(SA)胺的反应在44 wt%乙醇-水溶液中进行动力学研究,在25.0摄氏度,离子强度为0.2 M(KCl)。通过分光光度法(360 nm)释放2,4-二硝基苯氧根阴离子来研究反应。在胺过量的情况下,发现伪一阶速率系数(k(obsd))。k(obsd)对[胺]的图是线性的且与pH无关,斜率为k(N)。苯胺与MPDNPC和ClPDNPC的反应的布朗斯台德图(log k(N)vs pK(a)的铝离子)是线性的,斜率分别为β= 0.68和0.66,对于苯胺的反应,斜率为β= 0.44。 SA胺与ClPDNPC。后一种反应的斜率大小表明其机理是一致的。苯胺反应的斜率值在逐步机理和协同机理之间的边界处。logk(N)对非离去基团(beta(nlg))的碱性的敏感性为ca。-0.7对于苯胺