Solvent-dependent mechanistic aspects for the redox reaction of paraquat in basic solution,International Journal of Quantum Chemistry

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Solvent-dependent mechanistic aspects for the redox reaction of paraquat in basic solution
International Journal of Quantum Chemistry ( IF 2.3 ) Pub Date : 2021-06-18 , DOI: 10.1002/qua.26757
Hua Hou ₁ , Baoshan Wang ₁

Affiliation

Detailed mechanisms for the redox cycling of paraquat in basic solutions have been revealed computationally. The reduction of paraquat dication (PQ²⁺) undergoes via the successive additions with two hydroxide (OH⁻) anions to form the neutralized intermediates, which can decompose to generate the cation radical (PQ⁺) by releasing either OH or the hydrated O⁻ radical. PQ⁺ is neutralized by one OH⁻, converting molecular oxygen into superoxide (O₂⁻) anion to regenerate PQ²⁺. The reduction of PQ²⁺ by OH⁻ is an energy-directive process whereas the oxidation of PQ⁺ prefers an entropy-driving path in which OH⁻ acts as a catalyst. It is found that the Gibbs free-energy reaction paths are strongly solvent dependent. The redox cycle is energetically preferable in the solvents with low dielectric constants. The yellow-blue-transparent color-changing sequence in the clock reaction of paraquat has been understood by means of the electronic absorption spectra of the cations and the neutral intermediates. Atomic radical anion O⁻ is predicted besides the known OH and O₂⁻ radicals to stimulate experimental studies on the redox chemistry of paraquat.

中文翻译：

百草枯在碱性溶液中氧化还原反应的溶剂依赖性机理

已通过计算揭示了百草枯在基本溶液中氧化还原循环的详细机制。百草枯二阳离子 ( PQ ²⁺ )的还原是通过连续添加两个氢氧化物 (OH ^- ) 阴离子形成中和的中间体，中间体可以通过释放 OH 或水合的 O ^-分解生成阳离子自由基 ( PQ ⁺ )激进。PQ ⁺被一个 OH ^-中和，将分子氧转化为超氧化物 (O ₂^- ) 阴离子以再生PQ ²⁺。OH ^-对PQ ²⁺的还原是一个能量导向过程，而PQ ⁺的氧化更喜欢熵驱动路径，其中 OH ^-作为催化剂。发现吉布斯自由能反应路径强烈依赖于溶剂。在具有低介电常数的溶剂中，氧化还原循环在能量上是优选的。百草枯的时钟反应中黄-蓝-透明变色顺序已通过阳离子和中性中间体的电子吸收光谱得到理解。除了已知的 OH 和 O ₂^-自由基外，还预测原子自由基阴离子 O ^-以刺激对百草枯氧化还原化学的实验研究。

更新日期：2021-08-20

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