Insights into the effects of alcohols on hydrated electron (eaq−) generation from the p-benzoquinone/UV process

- The more efficient formation of p-hydroquinone from the UV photolysis of p-BQ in the presence of H2O was theoretically confirmed.
- Theoretical results indicate that the first triplet state of hydroxy-p-benzoquinone preferred to react with CH3OH at 4-position.
- In the CH3OH/p-BQ/UV process, CH3OH and p-BQ had a synergistic effect on the generation of hydrated electron.
- Hydrated electron was generated in the process with H2O and CH3OH as the original sources.

In this work, the effect of alcohols as hydrogen donors on hydrated electron (eaq−) generation from p-benzoquinone (p-BQ) photolysis was investigated by quantum chemical calculations and experiments to further understand the underlying mechanisms associated within the p-BQ/UV process. Theoretically, the UV photolysis of p-BQ at 253.7 nm in the presence of H2O could induce the formation of p-HOC6H4OH and hydroxy-p-benzoquinone, which was almost independent of the addition of CH3OH. While, the first triplet state of hydroxy-p-benzoquinone preferred to react with CH3OH (rather than H2O) to release the corresponding semiquinone radical and hydroxymethyl radical (CH2OH). These two radicals could induce the reduction of p-BQ to p-benzosemiquinone radical and thus enhanced the formation of p-HOC6H4OH as the precursor of eaq−. Experimentally, the detection of eaq− generated in the process was accomplished by the degradation of monochloroacetic acid (MCAA) (the probe of eaq−). With the addition of CH3OH, the degradation of MCAA was accelerated in the p-BQ/UV process. A similar acceleration was also observed by the addition of ethanol or 2-propanol with the α-H. However, tert-butanol, which is without the α-H in the structure, didn't induce the acceleration. Since the quinone-like and alcoholic groups are widely distributed in the environment, these findings may improve the understanding of the photochemistry of quinones in the presence of alcohols with the α-H.

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