MICELLAR CATALYZED HYDROLYSIS OF LITHIUM p-NITROPHENYL ETHYL PHOSPHATE (LiPNEF) AND THE PSEUDO PHASE ION EXCHANGE MODEL
Abstract:
<p align="justify"> The hydrolysis of lithium p-nitrophenyl ethyl phosphate (LiPNEF) was studied at 25°, 35°, and 45 °C by spectrophotometric techniques in the presence of micelles of cetyltrimethylammonium bromide (CTAB), sodium hydroxide, and salt. The concentration of NaOH used varied from 0,050 to 5,00 M and the NaCl ranged from 0,0050 to 0,030 M. Pseudo-first order rate constants (k<sub>w</sub>) and second-order rate constants (k<sub>2</sub>) and activation parameters such as Ea, ΔH<sup>≠</sup>, ΔG<sup>≠</sup>, and ΔS<sup>≠</sup> were measured. The system was also studied by tensiometric, viscosity, and quasi-elastic light scattering methods. At low concentrations of NaOH (below 0,55 M), the reaction can be explained in terms of conventional models of micellar catalysis, including the pseudo-phase ion exchange model. For a higher concentration of NaOH, conventional models of micellar catalysis are not applicable. In fact, at high hydroxide concentration, the system no longer contains micelles but liquid crystalline mesophases, and a model analogous to phase transfer catalysis appears to be more appropriate. </p>
<p align="justify"> The hydrolysis of lithium p-nitrophenyl ethyl phosphate (LiPNEF) was studied at 25°, 35°, and 45 °C by spectrophotometric techniques in the presence of micelles of cetyltrimethylammonium bromide (CTAB), sodium hydroxide, and salt. The concentration of NaOH used varied from 0,050 to 5,00 M and the NaCl ranged from 0,0050 to 0,030 M. Pseudo-first order rate constants (k<sub>w</sub>) and second-order rate constants (k<sub>2</sub>) and activation parameters such as Ea, ΔH<sup>≠</sup>, ΔG<sup>≠</sup>, and ΔS<sup>≠</sup> were measured. The system was also studied by tensiometric, viscosity, and quasi-elastic light scattering methods. At low concentrations of NaOH (below 0,55 M), the reaction can be explained in terms of conventional models of micellar catalysis, including the pseudo-phase ion exchange model. For a higher concentration of NaOH, conventional models of micellar catalysis are not applicable. In fact, at high hydroxide concentration, the system no longer contains micelles but liquid crystalline mesophases, and a model analogous to phase transfer catalysis appears to be more appropriate. </p>
DOI: 10.48141/SBJCHEM.v4.n4.1996.61_1996.pdf
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