N-15 AND C-13 NMR INVESTIGATION OF HYDROXYLAMINE-DERIVATIZED HUMIC SUBSTANCES

Five fulvic and humic acid samples of diverse origins were derivatized with N-15-labeled hydroxylamine and analyzed by liquid-phase N-15 NMR spectrometry. The N-15 NMR spectra indicated that hydroxylamine reacted similarly with all samples and could discriminate among carbonyl functional groups. Oximes were the major derivatives; resonances attributable to hydroxamic acids, the reaction products of hydroxylamine with esters, and resonances attributable to the tautomeric equilibrium position between the nitrosophenol and monoxime derivatives of quinones, the first direct spectroscopic evidence for quinones, also were evident. The N-15 NMR spectra also suggested the presence of nitriles, oxazoles, oxazolines, isocyanides, amides, and lactams, which may all be explained in terms of Beckmann reactions of the initial oxime derivatives. INEPT and ACOUSTIC N-15 NMR spectra provided complementary information on the derivatized samples. C-13 NMR spectra of derivatized samples indicated that the ketone/quinone functionality is incompletely derivatized with hydroxylamine.