Environmentally improved acid corrosion inhibitor

Composition useful for inhibiting corrosion of ferrous metals by acidic solutions comprising, by weight, (a) about 10% to about 30% cinnamaldehyde or substituted cinnamaldehyde, (b) about 20% to about 50% ethylene glycol (c) about 5% to about 20% C.sub.8-12 ethoxylated alcohols, and (d) about 1% to about 15% of a composition comprising about 10% to about 40% isopropanol and a reaction product (based on the total composition in this section (d)) of

• about 10% to about 40% of a ketone having 3-9 carbon atoms,
• about 1% to about 10% urea, thiourea or an alkyl-substituted thiourea,
• about 25% to about 50% benzaldehyde or formaldehyde calculated as a 37% solution,
• about 1% to about 10% HCl, said reaction being conducted in the presence of about 5% to about 20% ethylene glycol by warming the reactants in a vessel equipped with a reflux condenser, at a temperature slightly below that at which formaldehyede or benzaldehyde would collect in the condenser, and then refluxing the reaction mixture for at least six hours.