School of Chemistry, University of KwaZulu-Natal, Westville Campus, Chiltern Hills, P Bag X54001, Durban 4000, South Africa.
J Phys Chem A. 2011 Jul 14;115(27):7948-54. doi: 10.1021/jp202812f. Epub 2011 Jun 17.
The reaction mechanism of the oxidation of Amaranth dye (2-hydroxy-1-(4-sulfonato-1-naphthylazo) naphthalene-3,6-disulfonate) with hypochlorite under varied pH conditions was elucidated by a kinetic approach. Under excess concentration of oxidant, the reaction followed pseudo-first-order kinetics with respect to Amaranth, and the oxidation was found to occur through two competitive reactions, initiated by hypochlorite and hypochlorous acid. The reaction order with respect to both OCl(-) ion and HOCl was unity. While the latter reaction was fast, the significance of the oxidation paths depended on the relative concentration of the two oxidizing species, which was dictated by the reaction pH. The role of the H(+) ion in the reaction was established. For the hypochlorite ion and hypochlorous acid facilitated reactions, the second-order rate coefficients were 1.9 and 23.2 M(-1) s(-1), respectively. The energy parameters were E(a) = 33.7 kJ mol(-1), ΔH(‡) = 31.2 kJ mol(-1) and ΔS(‡) = -190.6 J K(-1) mol(-1) for the OCl(-) ion-driven oxidation, and E(a) = 26.9 kJ mol(-1), ΔH(‡) = 24.3 kJ mol(-1) and ΔS(‡) = -222.8 J K(-1) mol(-1) for the reaction with HOCl-initiated oxidation. The major oxidation products for both the pathways were 3,4-dihydroxy naphthalene-2,7-disulfonic sodium salt (P(1)), dichloro-1,4-naphthoquione (P(2)) and naphtha(2,3)oxirene-2, 3-dione (P(3)). On the basis of the primary salt effect and other kinetic data, the rate law for the overall reaction and probable reaction mechanism was elucidated. The proposed mechanism was validated by simulations using Simkine-2.
在不同 pH 条件下，通过动力学方法阐明了次氯酸盐氧化苋菜红染料（2-羟基-1-（4-磺酸钠-1-萘偶氮）萘-3,6-二磺酸钠）的反应机制。在氧化剂过量浓度下，反应对苋菜红表现为准一级动力学，并且发现氧化通过两种竞争性反应发生，由次氯酸盐和次氯酸引发。对 OCl(-)离子和 HOCl 的反应级数均为 1。虽然后者反应较快，但氧化途径的重要性取决于两种氧化物质的相对浓度，这由反应 pH 决定。确定了 H(+)离子在反应中的作用。对于次氯酸盐离子和次氯酸促进的反应，二阶速率系数分别为 1.9 和 23.2 M(-1) s(-1)。能量参数为 E(a) = 33.7 kJ mol(-1)，ΔH(‡) = 31.2 kJ mol(-1)和 ΔS(‡) = -190.6 J K(-1) mol(-1)，用于 OCl(-)离子驱动的氧化，E(a) = 26.9 kJ mol(-1)，ΔH(‡) = 24.3 kJ mol(-1)和 ΔS(‡) = -222.8 J K(-1) mol(-1)用于与 HOCl 引发的氧化反应。两种途径的主要氧化产物均为 3,4-二羟基萘-2,7-二磺酸钠盐（P(1)）、二氯-1,4-萘醌（P(2)）和萘并（2,3）环氧-2,3-二酮（P(3)）。基于主要盐效应和其他动力学数据，阐明了总反应和可能的反应机制的速率定律。使用 Simkine-2 进行模拟验证了所提出的机制。
