Pakistan Research Repository

PHYSICAL AND KINETIC INVESTIGATION OF MICELLAR EFFECTS ON THE REACTION OF P-NITROPHENYL PROPIONATE WITH HYDROXIDE ION

Hassan, Fouzia (1996) PHYSICAL AND KINETIC INVESTIGATION OF MICELLAR EFFECTS ON THE REACTION OF P-NITROPHENYL PROPIONATE WITH HYDROXIDE ION. PhD thesis, University of Karachi, Karachi.

[img]HTML
17Kb

Abstract

The micellar effect on the hydrolysis of para-nitrophenyl propionate (PNPP), was studied spectrophotometrically at 35°C in basic solution. The applicability of the electrostatic model was tested by determining the effect of differently charged and uncharged micelles on the observed rates of reactions. The effect of ionic surfactant was in the concentration range of 1X10-6M to 8X10-2M. The rates of p-nitrophenol formation by the reaction of PNPP with hydroxide in were also measured in the presence of polysorbates (Tweens) 20,40,60 and 80 between 1-6% w/v. The work was carried out in the presence of carbonate-bicarbonate buffer at pH 9.2. The effect of neutral inorganic electrolytes (sodium chloride, sodium acetate and sodium sulphate) on the rate of hydrolysis of PNPP in the absence and presence of cationic surfactants was also studied The CMCs of surfactants were determined by different methods. The CMCs were found to be decreased as the hydrophobic part of the surfactants was increased, which could be due to decrease of interfacial energy on micellization which is more longer chain than short ones It was concluded from the analysis of kinetic data that all cationic surfactants studied in this work increased the rate of hydrolysis of PNPP and the first-order rate constants go through maxima with increasing cationic surfactants in the region of 1X10-2M to 5X10-2M surfactant and then the effect decreased. Changes in micellar structure in this critical region were evidenced by viscosity studies. There was an increase in the viscosity in the order sodium chloride < sodium acetate < Sodium sulphate for all the kinetic profiles was observed for the anionic and nonionic surfactants where the hydrolysis rates were inhibited. The addition of various concentrations of sodium chloride, sodium acetate and sodium sulphate continuously suppress the maxima in the surfactant rate profiles irrespective of salts. The addition of 1.5-2M concedntration of all salts completely eliminated this maxima, which is quite striking effect of these electrolytes. Sodium sulphate was found to be much more potent inhibitor of cationic surfactants catalysis among, sodium chloride and sodium, acetate The partitioning behavior of PNPP between the micelles and the bulk solution of ionic surfactants was also studied to analyse the kinetic results

Item Type:Thesis (PhD)
Uncontrolled Keywords:micellar effects, p-nitrophenyl propionate, hydroxide ion, para-nitrophenyl propionate, micelle formation, polysorbates, cmc, pnpp
Subjects:Biological & Medical Sciences (c) > Medical Sciences (c2) > Pharmacy(c2.5)
ID Code:1336
Deposited By:Mr. Muhammad Asif
Deposited On:27 Jan 2007
Last Modified:04 Oct 2007 21:06

Repository Staff Only: item control page