THE SYNTHESIS OF DIPEPTIDE METHYL HISTIDYLPROLINE ESTER AS CORROSION INHIBITOR TOWARDS CARBON STEEL IN 1% NaCl SOLUTION

• Main Author: Astuti Ibrahim (NIM 205 05 002), Puji
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/6619
• Institution: Institut Teknologi Bandung

ABSTRACT: <br /> <br /> <br /> The corrosion occured inside carbon steel pipeline caused by the presence of water, carbondioxide and acid of the liquid that flew through the pipeline. Preventing corrosion inside the pipeline can be done by using substance called corrosion inhibitor. Corrosion inhibitor is an additive substance to the carbon steel pipeline system used to inhibit the corrosion on metal. One of the commercial corrosion inhibitors that has been widely used is oleic imidazole. This substance can interact with iron at the imidazole group, while the alyphatic group can interact with non-polar compound to inhibit the interaction between iron and water. Until today, only a few of corrosion inhibitors derived from organic compounds, thus the advanced research of organic subtances, either from nature, modification of natural compounds and new synthetic organic compounds need to be carried out. Histidine is one of amino acid compounds which has imidazole group that can be used as corrosion inhibitor. Proline also has the similar function as corrosion inhibitor as histidine due to its pyrrolidine group. These two compounds do not have the corrosion inhibition efficiency as expected, therefore to increase the corrosion inhibition efficiency towards carbon steel, in this research dipeptide methyl histidylproline ester was synthesized. <br /> <br /> <br /> The synthesis method used in this research to produce methyl histidine ester is the esterification of histidine with methanol using thionyl chloride (SOCl2) as activator. Furthermore the synthesis of dipeptide from methyl histidin ester and proline utilized dicyclohexylcarbodiimide (DCC) in N,N-dimethylformamide (DMF) solution. The substance was purified by column chromatography using dichloromethane and ethyl acetate (8:2) as eluents with Rf 0.4. The methyl histidin ester was characterized by its melting point, IR spectrum and its corrosion inhibition activity measurements utilized Tafel method in 1% NaCl solution induced by CO2 gas. The dipeptide product was characterized by its melting point, infrared (IR), ultraviolet (UV) and NMR (Nuclear Magnetic Resonance) spectra, and its corrosion inhibition activity measurements utilized Tafel method. <br /> <br /> <br /> Methyl histidine ester is a white crystal with melting point 180-182 oC and 89.97% chemical yield. Based on the IR spectra there was characteristic peaks of ester absorbance at 1750,8 cm -1 and 1230,3 cm -1. The dipeptide is a brownish yellow crystal with melting point 164-170 oC. Based on the structure elucidation of dipeptide utilized infrared, ultraviolet and NMR spectra, it was confirmed that the product was methyl histidylproline ester compound. The infrared spectrum showed the peak at 1676,1 cm -1 confirmed the presence of amide functional group of the structure of dipeptide. The proton NMR showed the hydrogen peaks of -NH group at chemical shift of 8.1 ppm and the carbon NMR spectrum proofed the presence of carbonyl ester and carbonyl peptide bond at chemical shift of 170.1 and 161.2 ppm, respectively. The measurements of corrosion inhibition activity of histidine, proline, methyl histidine ester and dipeptide methyl histidylproline ester showed that dipeptide has the highest corrosion inhibition activity of 50.76% at concentration of 8.8 ppm. Based on the measurements of corrosion inhibition activity at various concentration of dipeptide showed the optimum corrosion inhibition activity of 62.47% at 4.8 ppm. The interaction between pyrrolidine, imidazole, alyphatic group and amide bond in the structure of methyl histidylproline ester with the surface of carbon steel increased the corrosion inhibition activity of dipeptide, therefore synthesized dipeptide became the more potent corrosion inhibitor than histidine, proline and methyl histidine ester.