Corrosion inhibition of brass in presence of 1, 4, 5, 6-tetrahydropyrimidine derivatives in chloride solution

Abstract

The inhibition effects of L (-) aspartic acid (I) and its various derivatives namely N-benzenesulphonyl L (-) aspartic acid (II), α-benzenesulphonamido-β-2-(1, 4, 5, 6-tetrahydropyrimidinyl) propionic acid (III) and 1-benzenesulphonamido-1, 2-bis-2(1,4,5,6-tetrahydropyrimidinyl) ethane (IV) against the corrosion of brass in 0.6 M aqueous sodium chloride solution have been studied using potentiodynamic polarization and electrochemical impedance spectroscopy. The inhibition efficiency of these compounds increases in the order I < II < III < IV. The inhibition efficiency of IV with 4 × 10 ^-5 M concentration is the highest which reaches 94.9%. It is observed that the introduction of C₆H₅SO₂- group increases the inhibition efficiency of L (-) aspartic acid by 32.0%. Conversion of one –COOH group to 1, 4, 5, 6-tetrahydropyrimidine increases inhibition efficiency by 15.5% and when both the –COOH groups are converted to 1,4,5,6–tetrahydropyrimidine the inhibition efficiency becomes maximum (95%). This is due to higher molecular size, π – electron contribution of the benzene ring, and presence of more active adsorption sites.