Derivatization and structural studies by spectroscopic methods of humic acids from Leonardite

Humic acids (HA) from Leonardite were methylated with CH3I/Ag2O in a methan ol suspension (yield 261 +/- 23.6 g kg(-1); N = 4) and dimethylformamide (D MF) (yield 839 +/- 57.6 g kg(-1) N= 4) solution. Methylated humic acids are soluble in organic solvents and have been examined by IR-FT,H-1 and C-13-N MR spectroscopy methods. The OCH3/COOCH3 ratio was calculated by C-13-NMR f or HA methylated in methanol suspension and DMF solution obtaining values o f 0.38 and 0.82, respectively. Methylated acids molecular weight distributi on was measured by Size-Exclusion Chromatography (SEC). The product obtaine d in methanol suspension has a molecular weight (M-n) of 2918 Da and a disp ersion index (D = M-w/M-n) of 1.13. The methylated product prepared in DMF solution is characterized both by higher molecular weight, (M-n = 3623 Da) and dispersion index (D = 2.10). (C) 2000 Elsevier Science B.V. All rights reserved.