The oligomerization of 4-chloroaniline, a pesticide derivative, and guaiacol, a humus constituent

The oxidation of 4-chloroaniline, a pesticide derivative, and guaiacol, a humus constituent, produced a variety of oligomers and co-oligomers. The mode of formation and the structure identification of these oligomeric products was studied in order to more clearly characterize the fat of substituted anilines in the soil, the formation of humic materials, and the binding of substituted anilines to humus.;The oxidation of 4-chloroaniline and guaiacol in buffered aqueous solutions was catalyzed by soil enzymes. The resulting products were isolated from the solution by solid-phase extraction, separated by thin-layer chromatography, and their structures were determined using mass spectrometric and proton nuclear magnetic resonance spectroscopic analyses. Quantitation of the oligomeric products was achieved using reverse-phase high-performance liquid chromatography with direct-injection of reaction solution samples. Based on product structures, and their relative amounts, reaction pathway schemes which describe the initial stages for the oligomerization of 4-chloroaniline, of guaiacol, and the co-oligomerization of 4-chloroaniline and guaiacol, were proposed.;The oxidation of 4-chloroaniline resulted in the formation of four dimers, two trimers and two tetramers with benzoquinone monoimine, benzoquinone di-imine, diaminobenzene and azobenzene structures. The proposed oligomerization scheme shows that free-radical couplings initiate three reaction pathways, and the combined pathways account for the formation of all eight 4-chloroaniline-derived oligomers.;The guaiacol-derived oligomeric product mixture included five dimers and two trimers. The oligomers mostly had polyphenolic structures with carbon-carbon and carbon-oxygen linked monomers, and one dimer had a quinonoid structure. Free-radical couplings of the monomer are implicated in the formation of dimeric quinones which are subjected to nucleophilic substitution reactions, or are rapidly reduced to the polyphenolic compounds.;The oxidation of the combined 4-chloroaniline and guaiacol substrates led to the production of five co-oligomers, in addition to the seven guaiacol-derived oligomers. The four trimers and one tetramer had aminoquinone, iminodiphenoquinone and nitrogen heterocyclic structures. The co-oligomerization process is thought to involve reactions such as free-radical coupling, free-radical abstraction, Michael addition with subsequent tautomerization and oxidation, and cyclization of an aminohexadienone.