Three new 4-methoxybenzoylthiourea derivatives namely N-phenyl-N'-4-methoxybenzoylthiourea (A), N-(2-methoxy-phenyl)-N'-4-methoxybenzoylthiourea (B) and N-(2-nitrophenyl)-N'-4-methoxybenzoylthiourea (C) has successfully synthesized and characterized by elemental analysis, Fourier Transform Infrared (FTIR), proton ( 1 H) and carbon ( 13 C) Nuclear Magnetic Resonance (NMR) spectroscopy. Result obtained for IR showed the presence of important bands of the compounds such as ν(N-H), ν(C=O), ν(C-N) and ν(C=S) which were observed at 3200 cm -1 , 1670 cm -1 , 1200 cm -1 and 700 cm -1 , respectively. The 1 H chemical shifts for CONH and CSNH had been observed around 9 ppm and 12 ppm, respectively. For the 13 C resonance, the signal of C=O and C=S had been observed at 180 ppm and 200 ppm, respectively. The efficiency of the synthesized compounds was investigated as corrosion inhibitor of mild steel in 1.0 M H 2 SO 4 by using linear polarization resistance (LPR) technique.
The effect of new corrosion inhibitors, namely N-(2-methoxyphenyl)-N'-(2-methylbenzoyl) thiourea (A1). N-(3-methoxyphenyl)-N'-(2-methylbenzoyl) thiourea (A2), N-(4-methoxyphenyl)-N'-(2-methylbenzoyl)thiourea (A3) and N-(2-methylbenzoyl)-N'-phenylthiourea (A4) on mild steel in 1.0 M H 2 SO 4 with variation concentrations of inhibitors: 1 × 10 −5 , 1 × 10 −4 and 1 × 10 −3 M was tested by using weight loss method and linear polarization resistance (LPR) technique. These compounds were characterized using elemental analyser, FTIR, 1 H and 13 C NMR spectroscopy. Result obtained for IR showed the important bands of thiourea compound such as ν(N-H), ν(C=O), ν(C-N) and ν(C=S) which were observed around 3200, 1670, 1250 and 700 cm −1 . The 1 H chemical shifts for CONH and CSNH had been observed around 11 and 12 ppm respectively. For the 13 C resonance, the signal of C=O and C=S had been observed at 180 and 206 ppm. The presence of the inhibitors significantly reduced the corrosion rate of the mild steel. The most promising inhibitors action is at 1 × 10 −3 M and was achieved by compound A1 where the inhibition efficiency is 82.4-86.2 %. The effectiveness of the compounds was affected by the presence and absence of methoxy as the substituents in the compounds.
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