Synthesis of some new bisquaternary ammonium salts as acid corrosion inhibitors for carbon steel

A variety of bisquaternary ammonium salts was prepared for the first time by reacting N,N,N′,N′-tetraallyl-1, 6-hexanediamine with allyl chloride, propargyl chloride, benzyl chloride, and 1-bromododecane in excellent yields (>90 per cent). Inhibition efficiency for different concentrations of the synthesised compounds for the inhibition of corrosion of carbon steel in 1 M HCl exposed for 6 h at 60°C was determined gravimetrically. The bisquaternary salts exhibited excellent inhibition efficiencies (97-99 per cent) in the acidic solution containing 400 ppm of the inhibitor. Comparable results were obtained by the electrochemical method using Tafel plots for the inhibition efficiency of the synthesised compounds. The adsorption of these compounds on carbon steel surface was found to obey Temkin's adsorption isotherm. The work marked the beginning of constituting an important class of new inhibitors containing multiple adsorption centres of positive nitrogens as well as π-donor moieties.