Oxidation of β-aryl-and β-heteroarylpyruvic acids using sodium perborate tetrahydrate (SPB) in aqueous solution at ambient temperature gives the corresponding arylacetic acids in good yield (68–86%). The mild conditions are convenient for the preparation of thermally unstable acids. In particular the method has been applied to the preparation of an unstable 5- nitroimidazol-2-yl ethanoic acid which could not be obtained using other reagents ...