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Effects of pre-micelles of anionic surfactant SDS on the electron transfer reaction between methylene blue and ascorbic acid

机译:阴离子表面活性剂SDS的前胶束对亚甲基蓝与抗坏血酸之间电子转移反应的影响

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摘要

The effect of pre-micellar cluster of the anionic surfactant sodium dodecyl sulphate (SDS) on the electron transfer reaction between methylene blue (MB) and ascorbic acid (AA) in dilute acid medium has been investigated in the temperature range 298-308 K. The reaction is first order each with respect to MB as well as AA. The reaction involves two parallel paths - one uncatalyzed and the other H+-catalyzed path resulting in the rate law, k(obs) = (k(0) + k(1) [H+]) [AA] [MB]. Iodide ion has been found to have a specific accelerating effect on the reaction rate. The reaction appears to take place between undissociated AA molecule and MB+/HMB2+ cation. Anionic surfactant SDS shows an inhibiting effect on the reaction rate in the pre-micellar region, ultimately leading to a limiting value. The inhibiting effect of SDS has been explained in terms of Piszkiewicz's co-operativity model. The co-operativity index (n) value varies from 1.45 to 1.76 in the studied temperature range. The values of K-S (the dissociation constant of the pre-micelle), n and surfactant concentration lead to the fact that the electrostatic binding in the pre-micelle is reasonably strong and most of the MB molecules remain in the pre-micelle cluster before the electron transfer with AA takes place. The formation of pre-micelle is exothermic in nature and thus favored at lower temperature. (C) 2016 Elsevier B.V. All rights reserved.
机译:在298-308 K的温度范围内,研究了阴离子表面活性剂十二烷基硫酸钠(SDS)的胶束前簇对亚甲基蓝(MB)和抗坏血酸(AA)在稀酸介质中电子转移反应的影响。关于MB以及AA,该反应均为一阶。该反应涉及两条平行的路径-一个未催化的路径和另一个H +催化的路径,导致速率定律k(obs)=(k(0)+ k(1)[H +])[AA] [MB]。已经发现碘离子对反应速率具有特定的促进作用。该反应似乎发生在未离解的AA分子和MB + / HMB2 +阳离子之间。阴离子表面活性剂SDS对胶束前区的反应速率有抑制作用,最终导致极限值。 SDS的抑制作用已根据Piszkiewicz的合作模型进行了解释。在研究的温度范围内,合作指数(n)值在1.45至1.76之间变化。 KS(前胶束的解离常数),n和表面活性剂的值导致以下事实:前胶束中的静电结合力相当强,并且大多数MB分子在胶束前保留在胶束中用AA进行电子转移。胶束的形成本质上是放热的,因此在较低温度下是有利的。 (C)2016 Elsevier B.V.保留所有权利。

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