Title : The effects of oxalic acid in the extraction and isolation of ascorbic acid
Abstract:
Ascorbic acid (Vitamin C) decomposes on exposure to heat, is sensitive to light and is destroyed when exposed to atmospheric oxygen. Ascorbic acid was isolated from the aqueous extract of Casuarina equisetifolia (Australian pine needles) harvested from the main campus, university of Jos, Nigeria. Before extraction, the ascorbic acid content of the needles (leaves) was analysed to be (61.00±1.60) mg/100g. The extracts were uniformly divided into two portions. Oxalic acid was added to the first portion while the second portion contains only the extract. The first portion was labeled 1.0 and the second portion was 2.0. Isolation of the two samples was carried out gravimetrically and drying (lyophilization) was carried out with a freeze dryer because Ascorbic acid decomposes at high temperatures. The dried isolate was confirmed using UV-Vis, FTIR, GC-MS and H-NMR. The molar concentration of the ascorbic acid (0.02075±0.001, 0.02075±0.00025) mol/dm3 is the same for the extracts using the two methods after 7 days period. This shows that oxalic acid has no reaction with the ascorbic acid; it creates no interference to the titration process. The weight percents of the lyophilized isolates are (68.04g/500g, 13.608%) and (45.42g/500g, 9.084%) for methods 1.0 and 2.0 respectively. The UV-Vis determination gives weak peaks at 240nm and strong peaks at 300nm (λmax) for both methods. The FTIR spectra were analyzed. For this research, only the OHs and the lactone C=O (around 1750 cm-1) and C=C stretch (approximately 1680 cm-1) bands will be considered. Based on the results, these are observed only in isolate 1.0; this may be due to the decomposition of the ascorbic acid in isolate 2.0. The four OHbands observed in the isolated ascorbic acid 1.0 can be assigned as follows: C(1) OH-(3524.13, OHstretch, free hydroxyl (alcohol)), C(4) OH–(3404.48,OH- stretch, H bonded (alcohol)), C(3) OH-(3303.21, O-H stretch, H bonded (alcohol)), C(2) OH-(3022.28, OH stretch (carboxylic acid)) and the lactone C=O(1751.98 cm-1) and C=C stretch (1654.63 cm-1) bands. The GC-MS identified Ethane dioic, dimethyl ester (100%) which has a molecular formula C4H6O4 (m/z118.0880) with a base peak at m/z 8.0 for the method 1.0, with the possible loss of C2H2O2 (Acetolactone, a transient species of mass spectrometer) due to the temperature of the system. The GC-MS also identified isopropyl alcohol, tetramethyl silicate, ethane-dioic, dimethyl ester, and dimethyl fumarate, and dimethyl dimalate for isolate 2.0. The presence of fatty acids and their derivative in an isolate shows the pharmacological properties of the isolate. This research revealed that oxalic acid protected the isolated ascorbic acid from total decomposition. There was partial decomposition from the confirmatory titrimetric analysis (56.88% ascorbic acid) and the GC-MS analysis of 100% ester of oxalic acid, a major decomposition product of ascorbic acid. The FTIR analysis confirms that the compound isolated is ascorbic acid and further confirmation is derived from the UV-Vis. The H-NMR revealed the presence of the two essential protons (the most deshielded proton and the most acidic proton) in the structure of ascorbic acid when dissolved in methanol and deuterated DMSO and concentrated by sonication. The application of methods 1.0 and 2.0 was carried out to optimize the necessary conditions for maximum productivity.
