The Chemistry of High Molecular Weight Fulvic Acid Fractions

Abstract

Fulvic acid (FA) was methylated, dissolved in benzene, and fractionated over Al2O3 with the aid of organic solvents of increasing polarities. This paper is concerned with fractions eluted with ethyl acetate (III), ethyl acetate — methanol (1:1) (IV), and methanol (V), which were quantitatively the most abundant ones and which we consider as being most representative of the original FA. Each fraction was characterized by chemical and spectroscopic methods and by degradation with alkaline permanganate. Fractions IV and V were also degraded by NaOH hydrolysis and by alkaline CuO-oxidation. The degradation products were identified with the aid of a gas chromatograph — mass spectrometer — computer system.The number-average molecular weights of the three fractions were: III, 821; IV, 945; and V, 1,397. Infrared, proton n.m.r., and carbon-13 n.m.r. spectra provided, except for functional groups, little detailed information on the chemical structures of the fractions. The major degradation products were benzenecarboxylic and phenolic acids in addition to smaller amounts of aliphatic (mainly n-fatty) acids. Evidence is presented that may be interpreted to indicate: (a) esterification of some of the fatty acids to OH groups of phenolic acids; (b) the existence in the fractions of ether (C—O) linkages; and (c) rupture of C—C bonds during degradation. While in both the lower and the higher molecular weight FA fractions benzenecarboxylic and phenolic acids were the basic "building blocks", the latter appeared to be more complex and more stable in the higher-molecular weight fractions, possibly because chemical bonding as well as hydrogen bonding, van der Waal's forces, and π-bonding were involved simultaneously.