Active Species And Solvent Effect In Catalytic Oxidation Of Styrene

Solvents play a crucial role in redox reactions.Numerous studies have shown that solvents have a significant effect on catalytic activity and product distribution.The Gibbs free energy of the reaction was reduced by using a suitable solvent and the reaction rate was accelerated.Meanwhile,the catalyst and oxidant also interact with the solvent to affect the progress of the reaction.This work was systematically studied the effect of solvent on the decomposition of H₂O₂ into free radicals in the styrene reaction system,and explored the influence of free radicals on the distribution of styrene oxidation products.The final research results are as follows.1.The oxidation of styrene catalyzed by Cr-PKU-1In this research,the effects of reaction solvent,Cr doping amount,different metal doping,H₂O₂ dosage,reaction temperature and reaction time on the oxidation of styrene were discussed systematically.Under optimized reaction conditions:Experimental results showed that the type of reaction solvent has a decisive influence on product distribution.When DMF was used as the solvent,the styrene conversion was 58.0%,and styrene oxide selectivity was 53.3%.When CH₃CN was used as the solvent,the conversion of styrene was 49.6%,and the selectivity of benzaldehyde was 94.6%.2.The detection of Free radical in styrene oxidationMolecular probe methods were used to detect the relative content of?OH and?O₂^-free radicals in the reaction solution.The results showed that Cr³⁺sites in Cr-PKU-1were proved as a catalytic site to rapidly activate H₂O₂ to release two different active free radicals.Decomposition of hydrogen peroxide into free radicals was affected by the type of solvent.Combined with the results of catalytic experiments,it was found that hydroxyl radicals?·OH?were preferred to be formed in CH3CN and responsible for the formation of carbonyl compounds,while superoxide ion radicals?·O₂^-?were favored in DMF and beneficial to theepoxide production.In addition,the efficiency of hydrogen peroxide to decompose free radicals was affected by different metal ions,reaction time,Cr³⁺content,etc.all.3.The reaction mechanism of styrene oxidationThe relationship between the formation and conversion of the reaction product was explored.The experimental results showed that styrene oxide does not react under the experimental conditions?Conv.<2.0%?,indicating that benzaldehyde was mainly formed by the cleavage of carbon-carbon bonds,rather than the isomerization of epoxy groups.Based on the experimental results in this paper and the research in the literature,the mechanism of styrene oxidation reaction was deduced.Styrene oxide was formed by rearrangement of cyclic peroxide radical.