Humic acid oxidation products

The dissociation of water coordinated to exchangeable cations of clays results in Brtfnsted acidity. At low moisture content, the Brrfnsted sites may produce extreme acidities at the clay surface-As a result, acid-catalyzed reactions, such as hydrolysis, addition, elimination, and hydrogen exchange, are promoted. Base-catalyzed reactions are inhibited and neutral reactions are not influenced. Metal oxides and primary minerals can promote the oxidative polymerization of some substituted phenols to humic acid-like products, probably through OH radicals formed from the reaction between dissolved oxygen and Fe + sites in silicates. In general, clay minerals promote many of the reactions that also occur in homogenous acid or oxidant solutions. However, rates and selectivity may be different and difficult to predict under environmental conditions. This problem merits further study. 

Coal with a mean particle size of less than 3 mm is slurried with water and then oxidized with oxygen or mixtures of oxygen and air at temperatures ranging from 100° to 300° C, at partial oxygen pressures ranging from 0.1 to 10 MPa and reaction periods ranging from 5 to 600 minutes [425]. In the absence of catalysts, such as alkaline bases, the main products of oxidation are humic acids. 

Phenolic compounds have also been oxidatively polymerized to humic substances by clay minerals (29) and by the mineral fraction of a latasol (66). After a 10-day equilibration period, montmoril-lonite and illite clay minerals yielded 44 to 47% of the total added phenolic acids as humic substances whereas quartz gave only 9%. Samples of a latasol yielded over 63% of the total amount, from mixtures in varied proportion, of mono-, di- and trihydroxy phenolic compounds as humic substances (66). Extractions of the reaction products yielded humic, fulvic, and humin fractions that resembled soil natural fractions in color, in acid-base solubility, and in infrared absorption spectra. Wang and co-workers (67) further showed that the catalytic polymerization of catechol to humic substances was, enhanced by the presence of A1 oxide and increased with pH in the 5.0 to 7.0 range. Thus the normally very reactive products of Itgnin degradation can be linked into very stable humic acid polymers which will maintain a pool of potentially reactive phytotoxins in the soil. 

Figure 3. CuO oxidation products for soil humic acid Farmer (7) and Steelink (13)...

In this scheme, Reaction 1 represents a direct (pre-ignition) combustion reaction which may or may not be accompanied by formation of carbon monoxide Reaction 2 describes the oxidation reaction (and its sequences) examined in the present study. B and C in Reaction 2 denote degradation products of humic acids (e.g. hymatomelanic, fulvic, and/or so-called water soluble coal acids), and ki,, etc. represent the corresponding rate constants. 

Chlorinated organic compounds present in water, due to their carcinogenic nature, have become a great concern with respect to human health. Such substances are formed when humic acids react with chlorine in disinfection processes. Ozonation alone is generally not suited for the complete oxidation of chlorinated compounds because scavenger compounds such as acetic acid, formic acid, and oxalic acid can form and accumulate as by-products in the... 

Laboratory microcosms with Little Rock Lake sediments inoculated with 35S042- also show a gradual increase in organically bound 35S (< 1% to > 30% of reduced S over three months) and "CRS (20% to > 50%) whether incubated anaerobically or under oxic water columns. Sediments incubated under oxic water columns showed increasing incorporation of 3SS into fulvic and humic acids after a one-month delay (up to 30% of reduced S). Whether incorporation into fulvic and humic acids followed partial oxidation to polysulfides or elemental S (cf. 46-491 is not known. However, AVS accounted for < 10% of reduced 35S in our microcosms. Recent marine studies have also shown that H S (50-521 can be directly incorporated into acrylate, a breakdown product of i-mmethylsulphoniopropionate (DMSP), but the significance of this reaction in freshwater sediments has not been examined. 

Alberts, J.J., Filip, Z., Price, M.T., Hedges, J.I., and Jacobsen, T.R. (1992) CuO-oxidation products, acid hydrolysable monosaccharides and amino acids of humic substances occurring in a salt marsh estuary. Qrg. Geochem. 18, 171-180. 

The intermediate X, present in low concentration, is probably an aryl hydro-xylamine-O-sulphonate. The further oxidation products consistmainlyof polymeric humic acid. The stationary-state approximation applied to [X] shows that the ratio of the rate of formation of o-amino aryl sulphate to the rate of formation of other products is k3/k2[S20g ]", in qualitative agreement with the dependence of the yield of o-amino aryl sulphate on peroxodisulphate concentration, and the deviation from first-order kinetics with respect to peroxodisulphate towards the end of a run. 

Maximum dissolution of Fe and Mn oxides increasing sulfide production Co-precipitation of metals with FeS, and humic acid complexation... 

In general, commonly used oxidants destroy phenolic rings or give complex products (25, 26). Some of the oxidants such as nitrobenzene produce reaction byproducts that may interfere with the analysis of the oxidation products (23, 27, 28). To obtain lignin oxidation products from coals, we resorted to the alkaline cupric oxide oxidation method which has been applied successfully to analysis of lignins in plants (23), fulvic and humic acids (24, 27), and land-derived marine sediments (23). 

Although trihydroxybenzenes and their derivatives have been isolated from the oxidation products of lignins, humic acids, and land-derived marine sediments (5, 17, 23, 24, 27), it was found that 2,6-dimethoxy-... 

Some acids not found in oxidation products of lignins, land plants, and marine sediments were found in the oxidation products of coals. Among these were phenolic di- and tricarboxylic acids and hydroxy-naphthalenecarboxylic acids. From some soil fulvic and humic acids, phenolic poly carboxylic acids have been found in the oxidation products together with considerable amounts of fatty acids. Therefore, phenolic esters of fatty acids are considered to be present in these soil acids (6, 27). However, little or no fatty acids were observed in the coal oxidation products. 

Lignin Analysis. Lignin present in fulvic and humic acids from stream, foam, and foam-extract samples from Como Creek and the Suwannee River were oxidized to phenolic oxidation products by copper oxide oxidation via the method described by Hedges and Ertel (24). These phenolic oxidation products then were derivatized to trimethyl silyl derivatives for GC/MS analysis. 

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