One-Pot Electrocatalytic Oxidation Synthesis Of Nitriles From Alcohols Mediated By TEMPO

Nitriles are important compounds that are widely used as synthons of fine chemicals,pharmaceuticals,materials and agrochemicals.They are also vital intermediates for transformation to some functional groups,such as carboxylic acids,amines,amides and esters.Classical methods often suffer from several disadvantages:high reaction temperature was needed;low selectivity and use of toxic metal cyanides;stoichiometric oxidants were required.A kind of stable nitroxyl radical2,2,6,6-Tetramethylpiperidinyl-l-oxyl(TEMPO)is widely employed as a mediator in organic synthesis.It is well-known that electrochemical syntheses offer remarkable advantages such as high atom economy and less pollution.In this paper,we exploit a green strategy for one-pot electrocatalyticl oxidation synthesis of nitriles from alcohols mediated by TEMPO.One-pot electrochemical oxidation of alcohols to nitriles has been developed with ammonium acetate as the nitrogen source and2,2,6,6-tetramethylpiperidinyl-l-oxy(TEMPO)as the catalys in 0.1 M NaClO4-CH3 CN electrolyte under room temperature.Cyclic voltammetry investigation showed that TEMPO is electrochemically oxidized to TEMPO+ and an obvious redox reaction between alcohol and TEMPO occurs efficiently in the presence of ammonium acetate.In an effort to gain insight into the plausible reaction mechanism,reactions are studied by in-situ FTIR.Experiments show that the alcohol is first oxidized to the intermediate aldehyde and then further oxidized to the target product nitrile.We study the effect of electrolysis potential,catalyst and time on the catalytic system.The constant potential electrolysis of various functionalized alcohols,affords the corresponding nitriles in moderate to excellent yields at ambient temperature.A plausible reaction mechanism of one-pot electrochemical oxidation of alcohols to nitriles is proposed based on the result of experiments.Anoher one-pot electrochemical synthesis of nitriles from alcohols using hexamethyldisilazane(HMDS)in place of ammonium acetate as the nitrogen source in the presence of acetic acid is explored.The result indicates alcohols will directly react with HMDS to form trimethylsilyl-ethers in the absence of acetic acid.Thus,the addition of acetic acid is necessary for the formation of nitriles.Cyclic voltammetry investigation showed that an slow redox reaction between alcohol and TEMPO occurred efficiently in the presence of HMDS and acetic acid.We initiated this study by screening for the acidity of the solution,electrolysis potentia and time,the amount of catalyst and HMDS on the catalytic system.The Constant potential electrolysis result demonstrates various benzylic alcohols can afforded the corresponding nitriles in moderate to excellent yields at ambient temperature.Unfortunately aliphatic alcohols can not been converted to the corresponding nitriles under the standard conditions.