A fused ring compound having hydroxy, carboxylic acid and hydroxyalkyl substituent groups and the metal salts or complexes thereof. The hydroxyalkyl group is especially a hydroxymethyl group. The compound is prepared by reaction of the hydroxy carboxylic acid derivative with formaldehyde in an alkaline medium at a temperature of not more than 50.degree. C. The compounds, especially the metal salts or complexes thereof, can be used to provide corrosion inhibition of metals, for example iron.