Oxidation of aldehydes to the corresponding carboxylic acids can be performed highly efficiently at room temperature with 70% tert-butyl hydroperoxide (in water) in the presence of a catalytic amount of easily available ligand free CuCl in acetonitrile as solvent under very mild conditions. This oxidation protocol works well for various aldehydes including aliphatic aldehydes and aliphatic dialdehydes. © 2007 Elsevier Ltd. All rights reserved.