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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Reduction Potential of the tert-Butylperoxyl Radical in Aqueous Solutions
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Reduction Potential of the tert-Butylperoxyl Radical in Aqueous Solutions

机译：叔丁基过氧自由基在水溶液中的还原电位

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摘要

Rate constants for oxidation of tert-butyl hydroperoxide anion (t-BuO_2~-) by several oxidants were determined by pulse radiolysis. Rapid oxidation was found with N_3~· (4.4 * 10~8 L mol~(-1) s~(-1)) and ~·O~- (2.6 * 10~8 L mol~(-1) s~(-1), but others (Br_2~(·-), I_2~(·-), ClO_2~·, CO_3~(·-), C_6H_5N(CH_3)_2~(·+)) reacted much more slowly. Since the reduction potentials of these oxidants are much higher than that estimated for t-BuO_2~·, the observed rate constants suggest that the self-exchange rate for t-BuO_2~·/t-BuO_2~- is very slow and that it would be difficult to establish rapid equilibrium by pulse radiolysis with a suitable redox pair. There fore, to determine the reduction potential for this peroxyl radical, the forward and reverse rate constants for reaction 6, t-BuO_2~· + Fe(CN)_6~(4-) <->t-BuO_2~- + Fe(CN)_6~(3-), were measured independently. The forward rate constant was measured by kinetic spectrophotometric pulse radiolysis in N_2O-saturated solutions containing high concentrations of N_3~- (1 mol L~(-1)), t-BuO_2~- (0.4 mol L~(-1)), and varying concentrations of Fe(CN)_6~(4-) (0.012-0.036 mol L~(-1)) at pH 13.7. The rate constant k_6 was found to be 2.5 * 10~2 L mol~(-1) s~(-1). Such a low rate constant was possible to measure by pulse radiolysis only because the self-decay of t-BuO_2~· is very slow compared to those of other peroxyl radicals. The reverse reaction rate constant was measured by mixing the reactants and following the disappearance of Fe(CN)_6~(3-) in the presence of spin traps to remove the peroxyl radicals from the equilibrium. A rate constant of k_(-6) = 1.4 * 10~(-2) L mol~(-1) s~(-1) was derived. By taking the reduction potential of Fe(CN)_6~(3-)/Fe(CN)_6~(4-) as 0.459 V vs NHE for the conditions used in these experiments, we calculate E(t-BuO_2~·/t-BuO_2~-) = 0.71 V and E(t-BuO_2~·/t-BuO_2H) = 1.05 V at pH 7 and 1.47 V at pH 0. The rate constants for oxidation of Fe(CN)_6~(4-) and other compounds by various peroxyl radicals were then utilized for the estimation of the reduction potentials of these peroxyl radicals.
机译：通过脉冲辐射分析确定了几种氧化剂氧化叔丁基氢过氧化物阴离子（t-BuO_2〜-）的速率常数。 N_3〜·（4.4 * 10〜8 L mol〜（-1）s〜（-1））和〜·O〜-（2.6 * 10〜8 L mol〜（-1）s〜（ -1），但其他（Br_2〜（·-），I_2〜（·-），ClO_2〜·，CO_3〜（·-），C_6H_5N（CH_3）_2〜（·+））的反应要慢得多。这些氧化剂的还原电势远高于t-BuO_2〜·的估计值，观察到的速率常数表明t-BuO_2〜·/ t-BuO_2〜-的自交换速率非常慢，因此很难用合适的氧化还原对通过脉冲辐射分解建立快速平衡，因此，为确定该过氧自由基的还原电位，应确定反应6的正向和反向速率常数，t-BuO_2〜·+ Fe（CN）_6〜（4 -）t-BuO_2〜-+ Fe（CN）_6〜（3-）的独立测定，前向速率常数通过动力学分光光度法在含有高浓度N_3〜-的N_2O饱和溶液中进行脉冲光解。 1 mol L〜（-1）），t-BuO_2〜-（0.4 mol L〜（-1））和不同浓度的Fe（CN）_6〜（4-）（0.012-0.036 mol L〜（-1 ））在pH 13.7下。发现速率常数k_6为2.5 * 10〜2L mol〜（-1）s〜（-1）。仅通过t-BuO_2〜·的自衰变比其他过氧自由基的衰变慢，才可以通过脉冲辐射分解法来测量如此低的速率常数。通过混合反应物并跟踪Fe（CN）_6〜（3-）的消失（在自旋阱存在下）以从平衡中除去过氧自由基，来测量逆反应速率常数。得出k _（-6）= 1.4 * 10〜（-2）L mol〜（-1）s〜（-1）的速率常数。在这些实验中使用的条件下，通过将Fe（CN）_6〜（3-）/ Fe（CN）_6〜（4-）的还原电势设为NHE 0.459 V vs. NHE，我们计算出E（t-BuO_2〜·/在pH值为7时，t-BuO_2〜-）= 0.71 V，E（t-BuO_2〜·/ t-BuO_2H）= 1.05 V，在pH 0时为1.47V。Fe（CN）_6〜（4- ）和其他各种过氧自由基产生的化合物，然后用于估算这些过氧自由基的还原电位。

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