Various aromatic, aliphatic and conjugated aldehydes were transformed to the corresponding carboxylic acids with 70% t-BuOOH solution (water) in the presence of catalytic amounts (10 mol%) of Mohr's salt. This method possesses functional group compatibility, does not involve cumbersome work-up, exhibits chemoselectivity since other functional groups remain intact and proceeds under mild conditions. The resulting products are obtained in good yields within reasonable times. Copyright © 2011 John Wiley & Sons, Ltd.