The Research On One-pot Synthesis Of Esters From Aldehydes With Alcohols Catalyzed By N-hydroxyphthalimide

The carboxylic esters are widely used in chemical industrial applications such ashousehold chemical products, spices, paints, pharmaceuticals and polymers due to thesignificance. Up to now, carboxylic esters are traditionally prepared from activatedcarboxylic acids with alcohols catalyzed by lewis acid. Meanwhile, aldehydes are alsoreadily available and are bulk scale raw chemicals in industry. Esterification ofaldehydes with alcohols is an attractive alternative for organic chemistry. In recentyears, successful efforts have been made on the aldehyde oxidative esterification.However, these methods usually require the participation of transition metal catalystor strong oxidant, and have several shortcomings such as hazardous to theenvironment, high cost, tedious work up, harsh reaction conditions and timeconsuming. Developing a efficient, mild and green catalytic system for aldehydeoxidative esterification has significant implications.We firstly presented a highly efficient, mild, and environmental friendly protocolfor the oxidative esterification of aldehydes with alcohol catalyzed by NHPI-H2O2.The efficacy of the methodology is further demonstrated by esterification ofsubstituted aromatic aldehyde、aliphatic aldehyde and unsaturated aldehyde.The main contents of the article include:Firstly, we summarized the applications and synthetic methods of carboxylic acidester, and reviewed the research progress of NHPI catalytic system, then elaboratedthe significance of this paper and the catalytic method adopted.Secondly, we expounded the experimental process and post-processing methodsof the esterification of aldehydes with alcohols catalyzed by NHPI, and establishedthe GC/MS, GC analysis method for qualitative and quantitative analysis.Thirdly, we set the esterification reaction of benzaldehyde with methanol as anexample to established the catalytic system.Then, five reaction factors(the catalystdosage, substrate concentration, reaction temperature, reaction time, oxidant dosage,)were studied and optimized. And we determined the benzaldehyde (1mmol) withNHPI (12.5mol%) in methanol (10mL) added30%hydrogen peroxide solution (4.5mL) under the temperature of reflux within24hours is the optimal reaction conditions.the yield of ester can reach83%Fourthly, this method extends the esterification reaction between several different aldehydes with methanol with a satisfying catalytic effect. The results showthat in this NHPI catalytic system, electron-donating groups contribute to theoxidative esterification reaction and electron-withdrawing groups act in the contrarymanner. The yield of ester decreased with the increase of the molecular weight ofalcohols.The NHPI catalytic system also has good effect on the esterification ofaliphatic aldehyde and unsaturated aldehyde.Finally, combining with the experiment phenomenon and literature reported, apossible mechanism for NHPI catalytic system is proposed. The ester is generatedfrom the hemiacetal which losed H by PINO free radical.