The alkaline hydrolysis of humic substances

A humic and a fulvic acid were subjected to four successive hydrolyses with 2NNaOH solution at 170°C for 3 h. Following each hydrolysis, the degradation products were extracted into ethyl acetate, methylated, separated by chromatographic techniques and identified by mass spectrometry and micro-IR spectrophotometry.One g of humic acid yielded 113.5 mg of aliphatic compounds (mainly n-C₁₆ and n-C₁₅) fatty acids), 72.1 mg of phenolics (principally guaiacyl and syringyl derivative) 17.1 mg of benzenepolycarboxylic acid esters and 30.4 mg of N-containing compounds (mainly secondary aromatic amides). Repeated attacks by the alkali on 1.0 g of fulvic acid released 103.8 mg of aliphatics, 133.8 mg of phenolics, 27.0 mg of benzenecarboxylic but 181.8 mg of N-containing compounds. Most of the latter appeared to have been formed during the second, third and fourth hydrolysis which produced reactive compounds that could abstract N from diazomethane which was used as methylating reagent. While 25.0% of the initial humic acid resisted repeated attacks by the alkali, practically all of the fulvic acid was converted into ethyl acetate-soluble products. The alkali-resistant humic acid residue produced high yields of benzenepolycarboxylic acids on alkaline permanganate oxidation.Alkaline hydrolysis, which is known to cleave CO bonds, was found to be relatively specific, although not very efficient, for the degradation of structural phenolic humic and fulvic acid components and for the concomitant liberation of adsorbed aliphatics and N-containing compounds, but was relatively ineffective for degrading aromatic structures linked by CC bonds.