A perhydrolysis system is provided which includes peroxyacid precursors and a source of peroxygen. Upon dissolution in water these compositions provide high yields of a novel peroxyacid having the structure ##STR1## where R is hydrogen or an alkyl of not more than 5 carbon atoms. The precursor may include hydroxyl nitrogen derivatives as leaving groups, since the .alpha.-substituted phenoxy moiety enhances carbonyl reactivity toward perhydroxyl anion.