CuCl₂Catalyzed Oxidation Of Alcohols With TBHP: Direct Synthesis Of Acetals

The acetals are widely used in chemical industrial applications such as householdchemical products, spices, paints, pharmaceuticals and polymers. Up to now, acetalsare traditionally prepared from activated aldehydes with alcohols catalyzed by lewisacid. Meanwhile, aldehydes are also readily available in industry. Direct synthesis ofacetals from alcohols is an attractive alternative for organic chemistry. In recent years,successful efforts have been made on the synthesis of acetals from alcohols. However,these methods usually require the participation of transition metal catalyst or strongoxidant, and have several shortcomings such as hazardous to the environment, highcost, tedious work up, harsh reaction conditions and time consuming. Developing aefficient, mild and green catalytic system for aldehyde oxidative acetalation hassignificant implications.We firstly presented a highly efficient, mild, and environmental friendly protocolfor the synthesis of acetals from alcohols catalyzed by CuCl2-TBHP. The efficacy ofthe methodology is further demonstrated by oxidation of substituted aromaticalcohol、aliphatic alcohol and unsaturated alcohol.The main contents of the article include:Firstly, we summarized the applications and synthetic methods of acetals, andreviewed the research progress of CuCl2-TBHP catalytic system, then elaborated thesignificance of this paper and the catalytic method adopted.Secondly, we expounded the experimental process and post-processing methodsof the oxidation of alcohols catalyzed by CuCl2-TBHP, and established the GC/MS,GC analysis method for qualitative and quantitative analysis.Thirdly, we set the reaction of benzalcohol with methanol as an example toestablished the catalytic system.Then, five reaction factors(the catalyst dosage,substrate concentration, reaction temperature, reaction time, oxidant dosage,) werestudied and optimized. And we determined the benzalcohol (1mmol) with CuCl2·2H2O(2mmol) in methanol (10mL) added70%TBHP (5mL) under the temperatureof reflux within6hours is the optimal reaction conditions. the yield of Acetals canreach43%.Fourthly, this method extends the acetalation reaction between several differentalcohols with methanol with a satisfying catalytic effect. The results show that in this catalytic system, electron-donating groups contribute to the oxidative reaction andelectron-withdrawing groups act in the contrary manner. The yield of acetal decreasedwith the increase of the molecular weight of alcohols.Finally, combining with the experiment phenomenon and literature reported, apossible mechanism for CuCl2-TBHP catalytic system is proposed. The acetal isgenerated from the hemiacetal which losed H by free radical.