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DFT STUDY OF THE HYDROLYSIS OF SOME S-TRIAZINES
Citation:
Sawunyama, P. AND G W. Bailey. DFT STUDY OF THE HYDROLYSIS OF SOME S-TRIAZINES. Presented at 53rd Annual Meeting of the Southeastern Region of the American Chemical Society, Savannah, GA, September 23-26, 2001.
Impact/Purpose:
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.
Description:
The acid-catalyzed hydrolysis of atrazine and related 2-chloro-s-triazines to the corresponding 2-hydroxy-s-triazines was investigated using the B3LYP hybrid density functional theory method. Gas-phase calculations were performed at the B3LYP/6-311++G(d,p)//B3LYP/6-31G* level of theory. Gas-phase proton affinities, relative free energies of hydrolysis, enthalpies of hydrolysis, and activation energies were obtained. Proton affinities varied somewhat for different sites of protonation of atrazine (i.e., heterocyclic ring N1, N3, N5, and the side chain amine N atoms). N1 site exhibits the highest proton affinity (227.0 kcal mol-1) whereas side chain amine N atoms show the least proton affinity (ca. 209.3 kcal mol-1). The keto form of protonated hydroxyatrazine is 5.0 kcal mol-1 more stable than the enol form. Aqueous solvation effects were examined using Self-Consistent Reaction Field methods (SCRF). Structures were optimized at the B3LYP/6-31G* level using the Onsager model and solvation energies were calculated at the B3LYP/6-311++G(d,p) level using the isodensity surface polarizable continuum model (IPCM). The extent of solvent stabilization was greater for ionic species than neutral species. Likewise, solvation reduced the hydrolysis barrier of atrazine by 8.6 kcal mol-1.