CONICET | Buscador de Institutos y Recursos Humanos

Physicochemical characterization of hazardous compounds often is required for the development of structurereactivity correlations. Physical, chemical, and toxicological properties of target pollutants require determination for an efficient application of wastewater treatments. In the present work, we chose a chloro-nitro-aromatic derivative (4-chloro-3,5-dinitrobenzoic acid [CDNBA]), as a model compound on which to perform physicochemical and toxicological studies. Several properties of CDNBA are not available in the literature, although many aromatic nitro-compounds are considered hazardous materials. Measurements of solubility in water, acid dissociation constant, and kinetic parameters for the nucleophilic substitution of chlorine atom in alkaline media are reported. We also performed cytotoxicity studies of CDNBA and ultraviolet-irradiated CDNBA solutions. From the analysis of CDNBA solubility in water at different temperatures, an enthalpy of solution of 23.2 6 2.5 kJ/mol was found. The study of the acid dissociation constant Kc by using conductivity measurements and the modified Grans method yielded values for the equilibrium constant Ka of 2.36 3 1023 and 2.26 3 1023, respectively. The bimolecular rate constant for the reaction of CDNB2 and hydroxyl ion (HO2) measured at room temperature and 0.1 M of ionic strength was 5.92/M/s, and the activation energy for this process was 70.7 6 3.4 kJ/mol. Cytotoxicity assays with aqueous suspensions of Tetrahymena pyriformis showed lethal effects due to the pH change induced by CDNBA. On the other hand, in buffered solutions, a value of 104.47 mM was observed for the median effective concentration, that is, the concentration of CDNBA at which the proliferation was restricted to one half of the blank. Irradiation of CDNBA solutions increased the toxicity, suggesting the formation of intermediate products with higher cytotoxicity effects.

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