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SEDIMENT-ASSOCIATED REACTIONS OF AROMATIC AMINES. 2. QSAR DEVELOPMENT
Colon, D, E J. Weber, AND G. L. Baughman. SEDIMENT-ASSOCIATED REACTIONS OF AROMATIC AMINES. 2. QSAR DEVELOPMENT. ENVIRONMENTAL SCIENCE & TECHNOLOGY 36(11):2443-2450, (2002).
Elucidate and model the underlying processes (physical, chemical, enzymatic, biological, and geochemical) that describe the species-specific transformation and transport of organic contaminants and nutrients in environmental and biological systems. Develop and integrate chemical behavior parameterization models (e.g., SPARC), chemical-process models, and ecosystem-characterization models into reactive-transport models.
The fate of aromatic amines in soils and sediments is dominated by irreversible binding through nucleophilic addition and oxidative radical coupling. Despite the common occurrence of the aromatic amine functional group in organic chemicals, the molecular properties useful for predicting reaction kinetics in natural systems have not been thoroughly investigated. Towards this goal, the sorption kinetics for a series of anilines with substituents in the ortho-, meta- or para-positions were measured in sediment slurries. The sorption kinetics of the substituted anilines were characterized by an initial, rapid sorption process followed by a much slower sorption process. The initial rates of sorption varied with the type and position of the substituent group. Rate constants for the initial sorption process were correlated with molecular descriptors including ionization constants (pKa's), Hammett s-constants, polarographic half-wave potentials (E1/2), one-electron oxidation potentials (E1), highest occupied molecular orbital (HOMO) energies (EHOMO), and ionization energies (EIE). Based on the strength of linear correlations and the availability of data, ionization constants and Hammett s-constants appear to be the most useful molecular descriptors for predicting reaction rates of substituted anilines in the sediment slurries. The slow rates of sorption were much less sensitive to substituents effects than the rate constants for the faster sorption process suggesting that the slower process was not controlled by the rate of electron transfer (i.e., nucleophilic addition or radical formation), but was limited by the availability of covalent binding sites.