THE SYNTHESIS OF 2-PHENYL-4,5-DI(2-PYRIDYL)IMIDAZOLE, 2-PHENYL-4,5-DI(2-PYRIDYL)OXAZOLE, AND 2-(2-HYDROXYPHENYL)-4,5-DI(2-PYRIDYL)IMIDAZOLE AS CORROSION INHIBITORS TOWARD CARBON STEEL

• Main Author: Fatmawati Munazim, Iis
• Format: Theses
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/85981
• Institution: Institut Teknologi Bandung

Corrosion is the deterioration of materials by chemical interaction with their environment. In industry, particularly petrochemical industry, corrosion is one problem that inflicts loss and danger. Corrosion control and inhibition needs high cost and could be minimalized using existing technology through the application of best available practices, primarily through the use of organic compound inhibitors as imidazole and oxazole derivative compounds. The efficiency of various imidazole and oxazole derivatives as corrosion inhibitors was widely investigated and showed different results that associated with the molecular structure. The aims of the present work was to investigate the efficiency of 2-phenyl-4,5-di(2-pyridyl)imidazole (1), 2-phenyl-4,5-di(2-pyridyl)oxazole (2) and 2-(2-hydroxyphenyl)-4,5-di(2-pyridyl)imidazole (3), which have never been used as corrosion inhibitors. The compounds are considered to be effective corrosion inhibitors because its planar heterocyclic structures, having high electronic density, containing phi-electrons of conjugated double bonds, having hydrophobic properties, containing electronegative functional groups and the nitrogen atom with its lone pair electrons. Those properties would facilitate the good adsorption on the metal surface and increase the corrosion inhibition activity. The Synthesis of imidazole and oxazole derivative compounds conventionally is less effective and efficient. So it have been developed another synthesis method as Microwave Assisted Organic Synthesis (MAOS) which can lead to less by-products and/or decomposition products, the increase in the chemical yields and significantly speed up the reaction time. The synthesized products were analyzed using TLC (Thin Layer Chromatography), infrared, and NMR (Nuclear Magnetic Resonance) spectroscopy. Compound 1, 2, and 3 were successfully synthesized under microwave irradiation at 800 W output power as brownish yellow crystals. Reaction time is just about 1-3 minutes. The chemical yields of compound 1, 2, and 3 are, respectively, 83.55 %; 25.96%; and 23.60%, which represent a dramatic improvement over the conventional thermal heating method up to 198%. According to the results of TLC analysis and the narrow melting point range, it can be concluded that compound 1, 2, and 3 was pure. The determination of structures utilized infrared spectrum analysis to estimate the characteristic functional groups and NMR spectrum analysis to confirm the molecular structure accurately. The determination of corrosion inhibition activity of the synthesized compounds toward carbon steel utilized two electrochemical techniques, EIS (Electrochemical Impedance Spectroscopy) and Tafel, under various inhibitor’s concentrations and temperature. The corrosion inhibition efficiencies, calculated from these two techniques, are in reasonably good agreement and are very similar in the two cases, which indicated that the efficiency of an inhibitor increases with an increase in inhibitor’s concentration towards carbon steel in 1% NaCl solution. The adsorption of these inhibitors is also found to obey the Langmuir adsorption isotherm that is form monolayer on carbon steel surface. The inhibition mechanism is determined with ?Gads values. Compound 1, 2, and 3 showed the negative values of ?Gads, in a range between ?20 and ?40 kJ/mol, indicating a semi-chemical adsorption (semi-chemisorptions) mechanism of the corrosion inhibitor process. The data resulted from two electrochemical methods show that compound 3 has the best corrosion inhibition properties than compound 1 and 2, because it contain hydroxyl groups as electron donating group supplying a pair of electrons to the phi-electron system so that improve the interaction with metal surface. Whereas the least-effective inhibiting properties were shown by compound 2 because the interactions between oxygen atoms in the oxazole ring on iron surface is relatively weaker than the interaction between nitrogen atoms in the imidazole ring on iron surface. Although compound 1, 2, and 3 were found to be potential corrosion inhibitors, it still need further investigation to determine optimum condition so that enhance their inhibiting ability. Furthermore, the synthesis of another imidazole and oxazole derivatives should be performed to study comprehensively the relationship between the structure and functional groups of organic compounds, their adsorption on the metal surface, and their corrosion inhibition efficiencies.