Abstract: A method of making a peroxycarboxylic acid is described in which hydrogen peroxide is reacted with carboxylic acid in the presence of a catalyst acid to produce a reaction mixture containing peroxycarboxylic acid, unreacted carboxylic acid and the catalyst acid. This reaction mixture then is treated with ammonia to neutralize the catalyst acid, and the ammonium salt formed is removed in an aqueous phase. The mineral acid-free peroxycarboxylic acid reaction mixture may then advantageously be utilized as an oxidant. The peroxy-acids readily add oxygen to unsaturated compounds to produce epoxide compounds.