Accurate solubility measurements for the pesticide l-naphthyl-N-methylcarbamate (carbaryl) in water, natural and artificial seawater, NaCl, Na2SO4, CaCl2 and (CH3)4NBr, at different temperatures covering the range 5-45 °C, were obtained using a combination of the generator column method and absorption spectroscopy techniques. As a rule, it was found that the solubility of carbaryl in water and in the electrolyte solution increased with an increase in temperature.
The thermodynamic parameter ΔG°, ΔH°, ΔS°, and ΔC°p at 298.15 K, for the dissolution process carbaryl(s) to carbaryl(aq) and carbaryl(s) to carbaryl(aq. elect.), were calculated by fitting the solubility information to the Clarke and Glew equation. The results were consistent with the model which considers carbaryl and (CH3)4NBr to be solvent-structure-promoters and the rest of the electrolytes used in this work as solvent-structure-breakers.
The salt-effect as a function of temperature on the nonelectrolyte pesticide was obtained by calculating the Setchenov constants for each one of the electrolyte solutions mentioned above. Salting-out was observed in solutions prepared with NaCl, Na2SO4, and CaCl2 was well as in natural and artificial seawater, while salting-in was obtained with (CH3)4NBr solutions.
Pseudo-first order rate constants and half-life times for carbaryl in water were determined for different pH values ranging from 9.70 ± 0.02 to 11.60 ± 0.02 and covering the temperature range 25.5 ± 0.2 to 34.7 ± 0.2 °C.
A direct relationship between SDS concentration and pesticide solubility was found by showing that the presence of micelles increased the solubility of an otherwise sparingly soluble molecule like carbaryl.
Under high pressures (1356±34, 1797±34, and 2203±34 atm) and using NaCl as cosolute, carbaryl was readily degraded at 30 °C, giving deprotonated l-naphthol as one of the final products, in agreement with previous observations reported in the literature with esters and substituted phenols. Pseudo-first order high-pressure rate constants were calculated and, according to the results, it was found that there was a direct relationship between these constants and pressure.
| Identifer | oai:union.ndltd.org:pacific.edu/oai:scholarlycommons.pacific.edu:uop_etds-3102 |
| Date | 01 January 1984 |
| Creators | Huerta Diaz, Miguel Angel |
| Publisher | Scholarly Commons |
| Source Sets | University of the Pacific |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | University of the Pacific Theses and Dissertations |
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