THE SYNTHESIS OF DIPEPTIDE BENZOYLALANYLGLYCINE METHYL ESTER AS CORROSION INHIBITOR TOWARDS CARBON STEEL

• Main Author: Abdurrahman Hi Tahir, Juniarti
• Format: Theses
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/85978
• Institution: Institut Teknologi Bandung

Corrosion is one of major problems in petroleum mining and processing industry. A lot of catasthrophic cases was generated by corrosion, for example the damage of oil reservoirs, underground pipelines and other equipments. The pipelines used to trasport crude oil from reservoir to the processing installation were made by carbon steel that is irresistance towards corrosion. The best method to prevent corrosion that occurred at the inner parts of carbon steel pipelines is the use of inhibitor. Organic corrosion inhibitor have more advantages than inorganic corrosion inhibitor because it is easier to perform the degradation process by the environment. There are still small amount of studies in performing the synthesis of organic corrosion inhibitor. One of potent organic corrosion inhibitors is amino acids, however the presence of the acidic carboxylic acid groups could also induce the corrosion process, therefore it is necessary to perform the protection of carboxylic functional group. The protection of carboxylic functional group could increase the corrosion inhibition activity of amino acid. In this study, dipeptide compound of benzoylalanylglycine methyl ester has been synthesized. The synthesis takes place in three steps. The first step is the esterification reaction of glycine with methanol utilizing thionyl chloride (SOCl2) as activator, producing white crystalline of glycine methyl ester with melting point of 176.2oC. The characterizaton of glicine methyl ester was performed by IR and NMR showed charasteristic peaks and chemical shifts of ester C=O, ester C-O-C and primer –NH- functional groups. The second step is the benzoylation reaction of L-alanine using benzoyl chloride as reagent in basic condition producing transparent white crystalline of benzoyl alanine with melting point of 148.9oC. The IR spectrum of benzoyl alanine showed characteristic peaks of secondary –NH- and carboxylic –OH functional groups. The third step is the condensation reaction of glycine methyl ester and benzoyl alanine utilizing DCC (N,N’-Dicyclohexylcarbodiimide) to form white crystalline of dipeptide benzoylalanylglycine methyl ester with melting point of 112-113oC along with transparent white crystallyne of dipeptide benzoylalanylglycine with melting point of 186-187oC. The by product was formed because of hydrolysis reaction towards dipeptide benzoylalanylglycine methyl ester when extracted by aqua dm. The characterization of dipeptide benzoylalanylglycine methyl ester utilized IR and MS spectroscopy showed characteristic peaks of ester C=O (1751 cm-1), ester C-O-C (1184-1207 cm-1), whilst dipeptide benzoylalanylglycine showed characteristic peaks of carboxylic -OH (3068-2600 cm-1). The 1H-NMR spectrum of benzoylalanylglycine methyl ester showed the chemical shift of ester C-O-C at 3.70 ppm and secondary –NH- at 4.10 dan 4.80 ppm. The 13C-NMR spectrum of benzoylalanylglycine methyl ester showed the chemical shift of carbonyl ester at 168.20 ppm and carbonyl amide at 163.01 ppm and 160.64 ppm. Mass spectrophotometry (MS) data of benzoylalanylglycine methyl ester and benzoylalanylglycine showed fragmentation peaks of molecular mass ratio (m/e) of 264 and 250, respectively. The corrosion inhibition activities of the synthesized products were determined utilizing Tafel method and performed using Potensiostat/Galvanostat PGZ 301 instrument at the concentration of 8 ppm in 1% NaCl solution induced by CO2. gas. The corrosion inhibition efficiency of glycine methyl ester, benzoyl alanine, dipeptide benzoylalanylglycine methyl ester and dipeptide benzoylalanylglycine presents as follows, respectively: 63.34 %, 35.86 %, 68.40 % and 27.72 %. These results showed that the formation of dipeptide benzoylalanylglycine methyl ester, which derived from carboxylic protected glycine and amine protected alanine, increase the corrosion inhibition activity due to the loss of acidity center in the structure of glicine and L-alanine that would induce the corrosive environment towards carbon steel.