MICROWAVE-ASSISTED SYNTHESIS OF CHROMIUM(III) NICOTINATE COMPLEXES

• Main Author: ZULQARNAEN (NIM: 20512063) ; Pembimbing Dr. Deana Wahyuningrum, Irma Mulyani, Ph.D, MUHAMMAD
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/19018
• Institution: Institut Teknologi Bandung

A lot of variants of chromium(III) nicotinate complexes often used in dietary supplements for people with diabetes. In previous studies, it was observed that chromium(III) plays a role in the formation of insulin stimulation. However, chemical formula of chromium(III) nicotinate used in these supplements are often not fully determined. In this research, the synthesis of compounds of chromium(III) nicotinate complex used chromium(III) nitrate nonahydrate (Cr(NO3)3.9H2O) (1 mole equivalent) as a precursor/source of chromium(III), nicotinic acid (C5H4N-COOH) (3 mole equivalents) as ligand, and water as the solvent. The reaction of complex formation is done by reflux using microwave radiation energy (microwave-assisted synthesis). Reflux was carried out using a microwave power of 800 watts for 20 minutes. The color of the reaction mixture bedore microwave irradiation is turquoise which then turned into a royal blue after irradiation. Then the results of the reaction mixture was divided into four sections and, to each section, different amount of sodium carbonate (Na2CO3) is added, namely 2, 2½, 3, and 3½ mole equivalents of sodium carbonate. Once added sodium carbonate, all produce a purple product precipitate. Each product is called complex A, B, C, and D, respectively. Highest yield obtained in experiments using 2½ mole equivalents of sodium carbonate. <br /> <br /> <br /> <br /> <br /> Infrared spectroscopy analysis showed that the fingerprint region of infrared spectra of all complexes are similar to nicotinic acid, but unlike its precursor, so that it can be concluded that complexes of chromium(III) nicotinate have been formed. Infrared absorption of C=O groups on all of the resulting complex has the same value, namely at 1618 cm-1. Absorption of C=O at all the resulting complex is much lower than in the free ligand, which is at 1709 cm-1, so it can be concluded that the carboxylate group in the complex is located close to the metal ions (chromium(III)) and that nicotinate ligand bound to the chromium(III) through the carboxylate oxygen. Ultraviolet-visible light spectroscopy analysis of all complexes obtained either in solution or solid phase showed two absorption peaks in the visible light region ~413 nm and ~570 nm corresponding to the characteristic of d3 complex compounds and CrO6 octahedral coordination environment. In addition, UV-Vis spectroscopy analysis of the supernatant of reaction results still indicate the presence of free ligand that has not reacted. The presence of free ligand that has not reacted suggests that the amount of nicotinate per Cr3+ ion is less than three. Infrared and ultraviolet-visible light spectroscopy analysis showed that, in all four experiments, the chromium(III) nicotinate has <br /> <br /> <br /> <br /> <br /> v <br /> <br /> <br /> <br /> <br /> been formed and nicotinate ligand bound to the chromium(III) through oxygen in the carboxylic group. <br /> <br /> <br /> <br /> <br /> Mass spectrometry analysis showed each complex is not a mononuclear complex. Complex A and D produce similar mass spectra profiles. A complex showed peaks at m/z 613.48 and 641.51. Complex D showed peaks at m/z 613.50 and 641.53. The two peaks in the mass spectrum of compound A and D are not giving compatibility with any possible formulas. Complex B and C resulted mass spectrum with similar profiles. Complex B shows peak cation [M+H]+ at m/z 699.35. It looks similar to the mass spectrum of the complex C. Based on this analysis, obtained the molecular mass is ~698.34 for complex B or C. Based on that molecular mass, chemical formula obtained for complex B or C is [Cr2(OH)2(H2O)4(nic)4]. <br /> <br /> <br /> <br /> <br /> Chromium content of products have been determined by AAS. Chromium content of product A is 14.1%. Chromium content of product B is 14.1%. Chromium content of product C is 14.65%. Chromium content of product D is 14.5%. The result for product B or C is close to the theoritical calculation of chromium content of the formulas we proposed before, that is 14.89%. Those results imply that there are indeed two nicotinate ligans every Cr3+ and the rest ligans are aqua/hydroxide(s). The same conclusion are obtained for product A or D. The AAS analysis results are strengthening the result of Mass spectrometry analysis.