Dannan H, Crooks P A, Dittert L W, Hussain A
College of Pharmacy, University of Kentucky, Lexington 40536-0082.
J Pharm Sci. 1992 Jul;81(7):652-6. doi: 10.1002/jps.2600810712.
The kinetics and mechanisms of chlorine transfer from chloramine-T (CAT) to several amines are second order and independent of p-toluenesulfonamide concentration; thus, the reaction does not involve disproportionation of CAT to dichloramine-T. From the profile of pH versus rate, the following mechanisms were proposed: (1) reaction of the ionized species of CAT with the ionized amine (ionic mechanism) and (2) reaction of the un-ionized species of CAT with the un-ionized amine (nonionic mechanism). The second-order, pH-independent rate constants calculated for the ionic and nonionic mechanisms were 1.6 and 5 x 10(6) M-1 s-1, respectively. Although these two mechanisms are kinetically indistinguishable, the rate constant for the nonionic mechanism is of the same order of magnitude as those calculated for similar chlorination reactions involving nonionizable chloramines, such as N-chlorosuccinimide, N-chloroquinuclidine, and N-chloro-N-methylbenzenesulfonamide. The proposed mechanism for the chlorine exchange involves a molecule of water in a cyclic, six-membered transition state.
氯从氯胺 -T（CAT）转移至几种胺的动力学及机理为二级反应，且与对甲苯磺酰胺浓度无关；因此，该反应不涉及CAT歧化为二氯胺 -T的过程。根据pH对反应速率的曲线，提出了以下机理：（1）CAT的离子化物种与离子化胺的反应（离子机理）以及（2）CAT的非离子化物种与非离子化胺的反应（非离子机理）。为离子机理和非离子机理计算得到的二级、与pH无关的速率常数分别为1.6和5×10⁶ M⁻¹ s⁻¹。尽管这两种机理在动力学上难以区分，但非离子机理的速率常数与涉及不可电离氯胺的类似氯化反应（如N -氯代琥珀酰亚胺、N -氯代奎宁环和N -氯代 -N -甲基苯磺酰胺）所计算得到的速率常数处于同一数量级。所提出的氯交换机理涉及一个处于环状六元过渡态的水分子。
