Nitrosation and Nitration of Fulvic Acid, Peat and Coal with Nitric Acid

Abstract

Nitrohumic acids, produced from base extraction of coals and peats oxidized with nitric acid, have received considerable attention as soil ammendments in agriculture. The nitration chemistry however is incompletely understood. Moreover, there is a need to understand the reaction of nitric acid with natural organic matter (NOM) in general, in the context of a variety of environmental and biogeochemical processes. Suwannee River NOM, Suwannee River fulvic acid, and Pahokee Peat fulvic acid were treated with 15N-labeled nitric acid at concentrations ranging from 15% to 22% and analyzed by liquid and solid state 15N NMR spectroscopy. Bulk Pahokee peat and Illinois #6 coal were also treated with nitric acid, at 29% and 40% respectively, and analyzed by solid state 15N NMR spectroscopy. In addition to nitro groups from nitration of aromatic carbon, the 15N NMR spectra of all five samples exhibited peaks attributable to nitrosation reactions. These include nitrosophenol peaks in the peat fulvic acid and Suwannee River samples, from nitrosation of phenolic rings, and N-nitroso groups in the peat samples, from nitrosation of secondary amides or amines, the latter consistent with the peat samples having the highest naturally abundant nitrogen contents. Peaks attributable to Beckmann and secondary reactions of the initially formed oximes were present in all spectra, including primary amide, secondary amide, lactam, and nitrile nitrogens. The degree of secondary reaction product formation resulting from nitrosation reactions appeared to correlate inversely with the 13C aromaticities of the samples. The nitrosation reactions are most plausibly effected by nitrous acid formed from the reduction of nitric acid by oxidizable substrates in the NOM and coal samples.

Bacterial degradation of coal discard and geologically weathered coal

“…Shi et al (2012) showed that HNO 3 pre-treatment of coal decreases ash content and aromaticity but increases substrate porosity, oxygenation of aliphatic carbon, and the quantity of humic acid carbon. Also, solid state 15 N NMR spectroscopy has revealed that, in addition to nitro groups from nitration of aromatic carbon, products attributable to nitrosation reactions are evident in coal pre-treated with HNO 3 and, that secondary reaction products of the initially formed oximes are also produced (Thorn and Cox 2016). Although the mechanism underlying coal nitration remains poorly understood, the last step in the oxidation of phenol with nitrous acid regenerates nitrous acid which will continue to react as a nitrosating agent.…”

New 1H-benzimidazole-2-yl hydrazones with combined antiparasitic and antioxidant activity

“…Reported chemical shis for nitrosamine compounds are above 500 ppm on the ammonia scale. 43 Other studies reported for simple symmetrically-substituted nitrosamines NMR shis from À107.2 to À146.7 ppm for N1(-N]O) and from +154.6 to +175.9 ppm for N2(]O), referenced to 15 NO 3 Na. 44 In unsymmetrically substituted nitrosamines N1 resonates respectively from À103.7 to À153.6 ppm, while N2from +157.0 to +176.9 ppm.…”

Molecular Tagging for the Molecular Characterization of Natural Organic Matter

“…In general, the river samples gave the highest amounts of secondary nitrosation products, while the coal samples gave the least. 82 Nitration of NOM using 15 N-labeled reagents could be of use as a molecular tagging method for structure elucidation, as it is complementary to hydroxyl modifying methods, but greater control over the specificity of the reaction by using alternative reagents would be desirable. A recent review by Liu lists alternatives that could be tried.…”