Electrosynthesis Of Nitriles From Corresponding Aldehydes Mediated By TEMPO And KI

The nitrile group is considered to be a vital functional group in organic chemistry as it not only forms part of many important fine chemicals,pharmaceuticals,materials and agrochemicals,but also serves as an intermediate in the preparation of several functional groups.The traditional methods to synthesize nitriles usually suffer from severe reaction conditions,or use of hazardous reagents and expensive catalysts.Thus,from both economic and environmental viewpoints,there is an urgent need for more efficient and greener methods.Because aldehydes are readily accessed and easy to handle,synthesis of nitriles from corresponding aldehydes is one of the most recognized strategies in organic chemistry.2,2,6,6-Tetramethylpiperidinyl-l-oxyl?TEMPO?,as a kind of stable nitroxyl radicals,is widely employed as a mediator in electrochemical synthesis.In this paper,A simple synthesis method of nitriles from corresponding aldehydes by electrochemical oxidation was developed with ammonium acetate as the nitrogen source and 4-acetamido-2,2,6,6-tetramethylpiperidinyl-l-oxy?4-AcNH-TEMPO?as the catalyst.High electrocatalytic activity of 4-AcNH-TEMPO for oxidation of benzaldehyde to benzonitrile was disclosed by cyclic voltammetry measurements and the electrocatalytic oxidation became faster with increase of the benzaldehyde concentration.On the basis of in situ FTIR data and cyclic voltammetry experiments,a reaction mechanism,involving the redox of 4-AcNH-TEMPO and the generation of intermediate imine during the reaction,was proposed.Benzaldehyde reacted with ammonium acetate to give benzenemethanimine which could be converted into benzonitrile by oxidation reaction with 4-AcNH-TEMPO+.At the same time,4-AcNH-TEMPO+ was reduced to 4-AcNH-TEMPOH.In addition,various aldehydes were efficiently oxidized to their corresponding nitriles in 0.1M NaClO4/MeCN solution by preparative electrolysis experiments.The results showed that the present method exhibited high electrocatalytic activity and selectivity for oxidation of aldehydels to nitriles,especially for those aromatic aldehydels.Molecular iodine is an attractive catalyst as it is cheap,readily available and less toxic.In this paper,a novel electrochemical route to generate nitriles from aldehydes under mild conditions using KI as the mediator and ammonium carbonate as the nitrogen source has been developed.The electrochemical reaction was investigated by cyclic voltammetry and the consumption of I₂ as the electrochemical redox mediator on Pt electrode was confirmed.In an effort to gain insight into the plausible reaction mechanism,in-situ FTIR experiments were carried out and the intermediates of the reactions were observed through the formation of imine between?NH4?2CO3 and aldehydes,which further reacted with iodine to form N-iodo aldimine and finally transforms into nitrile by ?-elimination of HI.This electrocatalytic reaction system provided an efficient protocol for synthesis of nitriles at room temperature.