The oxidative cleavage of terpenes and unsaturated fatty acids into carbonyl compounds is an industrially interesting reaction. We have developed a metal-free protocol that can oxidatively cleave unsaturated fatty acids, terpenes and a variety of other alkenes into carboxylic acids in a synthetically straightforward, one-pot protocol. Near stoichiometric amounts of a combination of oxone and periodate are used in aqueous acetonitrile without additional additives, acids or emulsifiers. The solvent system and the reaction temperature have a profound influence on the reactivity of the substrates; conditions have been optimized for a broad scope of alkenes. The products can be isolated by simple extraction with an organic solvent without additional purification: the carboxylic acids are obtained in high yield (80–96%) as colourless solid or liquid products.