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Solvent‐dependent mechanistic aspects for the redox reaction of paraquat in basic solution
Author(s) -
Hou Hua,
Wang Baoshan
Publication year - 2021
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.26757
Subject(s) - chemistry , paraquat , redox , radical , photochemistry , dication , solvation , solvent , gibbs free energy , radical ion , hydroxide , hydroxyl radical , inorganic chemistry , ion , organic chemistry , physics , quantum mechanics
Detailed mechanisms for the redox cycling of paraquat in basic solutions have been revealed computationally. The reduction of paraquat dication ( PQ 2+ ) 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 (O 2 − ) anion to regenerate PQ 2+ . The reduction of PQ 2+ 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 O 2 − radicals to stimulate experimental studies on the redox chemistry of paraquat.