Synthesis and Corrosion Inhibition Studies of Benzoyltiourea Derivatives on Mild Steel in 1.0 M HC1

Eight derivatives of thiourea namely: l-cyclohexyl-3-( 4-fluorophenyl)thiourea (Tl), 1-( 4-fluoro-benzoyl)-3-( 4-fluorophenyl)thiourea (T2), 1-( 4-fluoro-benzoyl)-3-( 4- nitrophenyl)thiourea (T3), 1-( 4-chloro-benzoyl)-3-( 4-nitrophenyl)thiourea (T4), 1-( 4- bromophenyl)-3-( 4-chloro-benzoyl)thiourea (TS), 1-( 4-chloro-benzoyl)-3-( 4- bluorophenyl) thiourea (T6), 1-( 4-chloro-benzoyl)-3-(3-chloro-2-fluoro-phenyl)thiourea (T7), and 1-( 4-chloro-benzoyl)-3-(6-chloro-2-fluoro-3-methoxy-phenyl)thiourea (TS), were successfully synthesized and characterized via micro elemental analyzer, FTIR, 1H and 13C NMR spectroscopy methods. From the FTIR spectral data, the compounds are common to have the vibration frequency of stretching of v(N-H) around 3500- 3100 cm- 1, v(C=O) around 1660-1720 cm- 1, v(C=S) around 680-1440 cm- 1 and v(C-N) in the range of 1350-1000 cm- 1 . Three of the eight compounds which are T6, T7 and TS were selected for fu1ther study on their anticorrosion activity. The inhibition property of the resulted compounds on the corrosion of mild steel in I M hydrochloric acid has been investigated at room temperature using weight loss, potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS). It was found that, all the synthesized thiourea derivatives are capable to inhibit the corrosion of mild steel. It was found that the inhibition efficiency increases with inhibitor concentration and maximum efficiency was obtained at concentration 0.0004 M. Among the studied inhibitors, TS shows the best inhibition efficiency of greater than 90 %. The impedance spectra indicate that the inhibition process was attributed to the formation of an adsorbed film that protects the metal surface against corrosive medium. The potentiodynamic study reveals that the compounds studied acts essentially as mixed type inhibitor which inhibits both the cathodic and anodic parts of the corrosion reaction.