Synthesis and corrosion inhibition of α-amino acids alkylamides for mild steel in acidic environment

New compounds of alkylamides derived from a-amino acids were tested as corrosion inhibitors for carbon steel in an aqueous solution of hydrochloric acid. The chemical synthesis of these amides performed by aminolysis of alpha-amino acid methyl esters resulted in good yields. Electrochemical testing was carried out using polarization scans and weight loss measurements. Polarization scans indicated that compounds act as mixed corrosion inhibitors with an efficiency of 80-90% when dissolved in the testing solution at >= 50 ppm, whereas gravimetric results displayed a similar tendency. Microtox testing indicated a correlation with the molecular structure of inhibitors. Apparently, a long aliphatic chain (C > 12) promoted not only higher corrosion efficiency, but also a higher toxicity. The higher efficiency of dodecyl amine of tyrosine was apparently derived from its longer aliphatic chain, with some contribution from its phenyl ring, which reinforces the molecular interactions of pi type bonding to the d orbital metal favouring film formation. (C) 2008 Elsevier B.V. All rights reserved.