Abstract

The cyclohexane oxidation by H₂O₂ using VO(acac)₂ as starting catalyst in the presence of oxalic acid (OA) was studied. The dissociation of OA and VO(oxalate) formed in situ by interaction of VO(acac)₂ with OA is the essence of the electrical conductance G elevation (or vice versa 1/G dropping). As follows from the electronic and cyclic voltammetry spectra taken alongside 1/G, the substitution of weak field ligands (acac) of VO(acac)₂ by the middle-field (oxalate) ones strengthens the cation-ligand bonds and postpone the irreversible catalyst oxidation. In the absence of OA, 1/G was several times larger than the value intrinsic to VO(acac)₂ + OA mixture. The last feature corresponds with the considerable process productivity enhancement in presence of OA. The experimental part of this work was complemented with DFT calculation of the key quantum chemical characteristics as catalyst d-d-splitting, HOMO–LUMO gap and Gibbs energy. Bringing together the experimental and theoretical data led to deduce that the oxidation process efficiency relates, among others, with the modification the outer-sphere electronic configuration of metalocomplexes possibly leading to metal-peroxo species e.g. VO(η²-O₂) generation. On the other hand, oxalate anions, besides decreasing 1/G, may facilitate the cations and H₂O₂ interaction. Mentioned peculiarities may be responsible for the noteworthy yield enhancement in the presence of OA.

Graphic abstract

中文翻译：

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环己烷氧化：过程效率与电导率，反应混合物的电子伏安和循环伏安光谱的关系

摘要

研究了在草酸（OA）存在下，以VO（acac）₂为起始催化剂，通过H ₂ O ₂氧化环己烷。VO（acac）₂与OA相互作用原位形成的OA和VO（草酸盐）的解离是电导G升高的本质（反之亦然1 / G下降）。从1 / G旁取的电子和循环伏安光谱可知，用中场（草酸酯）取代VO（acac）₂的弱场配体（acac）增强了阳离子-配体键，推迟了不可逆催化剂氧化。在没有OA的情况下，1 /G比VO（acac）₂  + OA混合物的固有值大几倍。最后一个特征与存在OA时显着提高过程生产率相对应。这项工作的实验部分得到了DFT计算的补充，这些计算包括催化剂dd分裂，HOMO-LUMO间隙和Gibbs能量等关键量子化学特征。汇集了实验和理论导致数据推断，氧化过程效率涉及，除其他外，与修改metalocomplexes可能导致金属过氧物种例如VO（η的外球体的电子构型² -O ₂）的产生。另一方面，草酸根阴离子除了减少1 /G 1可以促进阳离子与H ₂ O _2的相互作用。提及的特殊性可能是在存在OA的情况下显着提高产量的原因。

图形摘要