Novel class of bisquaternary ammonium salts in inhibition of mild steel corrosion in HCl and H ₂SO ₄

A series of new bisquaternary ammonium inhibitor molecules p-xylylenebis[trialkylammonium chloride] were prepared in excellent yields by reacting α,α'-dichloro-p-xylene with a group of tertiary amines such as N,N-diallyl-N9-formyl-1,12-diaminododecane, N,N-diallyl-, N,N-diethyldodecylamine and N-dodecylpyrrolidine. Inhibition efficiencies (IEs) for different concentrations of bisquaternary salts for the inhibition of corrosion of mild steel in 1, 4 and 7.7M HCl as well as 0.5M H ₂SO ₄ exposed for 6 h at 60°C were determined gravimetrically. While in the presence of 400 ppm all the inhibitor molecules exhibited excellent %IEs of ≥99 in 1M HCl, p-xylylenebis[N,N-diallyl, N-dodecylammonium chloride] provided very good %IE of 97 and 94 respectively in 4 and 7.7M HCl. The inhibitors imparted good to very good IE in arresting mild steel corrosion in 0.5M H ₂SO ₄; p-xylylenebis[N,N-diallyl, N-dodecylammonium chloride] performed the best, giving %IE of 94 at 400 ppm. The interactions of the π electrons in the diallyl moiety with the low lying vacant d orbitals of iron help the inhibitor molecules to undergo adsorption and interfere with the anodic dissolution process. Comparable results for the IEs were obtained by the electrochemical method using Tafel plots of the synthesised compounds. The adsorption of these compounds on the mild steel surface was found to obey Frumkin and Temkin adsorption isotherms in 1M HCl and 0.5M H ₂SO ₄ respectively.