Antioxidant activity of Lignin -Mannich bases Synthesised by Amination reactions

G. K. Oloyede, B.O. Ogunsile, M.S. Ali, W.A. Ngouonpe

Abstract


 Lignin is a polymer derived from the phenylpropanoid compounds, coniferyl alcohol and related alcohols. It is the second abundant (next to cellulose) and important organic substance in the plant world. Researches on lignin has been in the area of adsorption properties, but this present study is aimed at synthesizing Mannich bases by amination reaction and investigating the antioxidant activities. Lignin was extracted from Nypa fruticans Wurmb. by soda pulping method. The lignin was subjected to Mannich reaction. The Lignin Mannich Bases (LMB) prepared were screened for antioxidant activity using 2,2-diphenylpicryl hydrazyl radical (DPPH) method. Results obtained showed that the Mannich bases prepared had the following monolignol units:   methylamine (LMB1), dimethylamine  (LMB2), diethylamine (LMB3),      aniline  (LMB4),  2,6—dimethylaniline (LMB5),    3,4-dimethylaniline (LMB6), 2,5-dimethylaniline (LMB7), 3,4-dichloroaniline (LMB8),  2,6-dichloroaniline (LMB9),  and  2-(3,4-dimethoxyphenyl) ethylamine (LMB10), respectively as evidenced in the Proton NMR data. Antioxidant activity showed that all the Lignin Mannich Bases had better activity than lignin and of comparable activity with standard Butylated hydroxyl anisole (BHA) with 75.64% inhibition at 1.0 mg/mL However, LMB4 (74.31%), LMB6 (72.98%), LMB7 (71.46%) and LMB3 (71.03%) which showed significant activity at this concentration. This present study has therefore been able to synthesize new Mannich bases from Lignin, a renewable natural resources and establish the potential of lignin and its amination products as antioxidants.
Keywords: Nypa fruticans, lignin; amines; antioxidant; butylated hydroxyl anisole

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Chemical Society of Nigeria