Study On Oxidative Cleavage Of Styrene Compounds Into Carbonyl Compounds

Aromatic aldehydes play a very important role in the organic synthesis of fine chemicals and medicine.They are commonly prepared by the oxidation of toluene and benzyl alcohol or benzene is used as raw materials for preparation through the reaction with carbon monoxide under pressure.In natural products,most compounds have carbon-carbon double bonds.Under this background,researchers have done a lot of research on the preparation of aldehydes by olefin oxidation.However,due to the low activity and low regional selectivity of olefin or the need to add expensive precious metals into the reaction,the large-scale application of the reaction is limited.Therefore,the selective oxidation of olefins to aldosterone compounds with high activity and regional selectivity is of great significance.Through literature review and previous work,this paper summarizes the research progress of epoxidation and oxidation fracture of olefin to carbonyl compounds.The oxidative cleavages the C=C double bond ofα,β-unsaturated carbonyl compound with or without metal catalyst was studied.Without a metal catalyst was studied under the condition of containing conjugated double bond of styrene compounds,and heterocyclic alkenes double bond oxidation fracture.Mn-Salen as catalyst,TBHP as initiator,O₂as oxidant,biphenyl as internal standard substance through liquid phase detection to determine the reaction conversion rate,selectivity and yield.It was found that the C=C double bond ofα,β-unsaturated carbonyl compounds was oxidized to aldehydes with high selectivity and conversion.With cinnamic acid methyl ester as reaction substrate on the optimization of reaction conditions,better reaction conditions as follows:1.Eq TBHP,diethylene glycol dimethyl ether as solvent,1 mol%Mn-Salen,reaction temperature 160℃.Under the reaction conditions to expand the 3-（4-substituted phenyl）-1-phenyl-acetone,3-（4-substituted phenyl）-acrylic acid,2-substituted phenyl acrylic acid and5-（4-substituted-benzyl）-1,3-dimethyl-pyrimidine-2,4,6-triketone substrate series.Experiments show that the oxidation method has a wide applicable scope,whether connected with double bonds on the benzene ring with electron-withdrawing or electronic group,or groups on the double bond is introduced into a steric hindrance,C=C double bond with high conversion rate and yield into carbonyl compounds.At the same time,it was found that the olefin oxidation cracking reaction could also be carried out without Mn-Salen catalysis,and better conversion and yield could also be obtained.TBHP as the initiator,O₂as oxidant,in the absence of metal catalyst the four kinds ofα,β-unsaturated C=C double bond of carbonyl compound oxide cracking into the corresponding carbonyl compounds,has high selectivity and good chemical functional group tolerance.When the substrates are styrene conjugated double bonds,the double bonds generate diphenylketone and the corresponding benzaldehyde with good conversion and selective reaction.However,when the heterocyclic olefin was used as the research object,side reactions occurred under the reaction conditions,leading to a decrease in reaction selectivity.The study on the reaction mechanism shows that the reaction is free radical mechanism.We hypothesized that the mechanism was firstly that TBHP was homopolyzed to a tert-butyl peroxide radical under high temperature,and then the single electron transfer with olefin occurred to generate a carbon radical,and then the oxygen was captured to generate an intermediate transition state of a quaternary cyclobioxane bridge,and finally it was decomposed to carbonyl compounds by heat.