<p>Aromatic compounds of the general formula <IMAGE> in which R and Ro represents a hydrogen atom or an alkyl radical of 1 to 4 carbon atoms are hydroxylated by reaction with hydrogen peroxide in the presence of a catalytic amount of a strong acid and the reaction is carried out in the presence of an activator which is a juxtanuclear aromatic aldehyde or derivative thereof selected from an acetal or a benzhydrol.</p>
