Dissertation
Factors affecting the alkaline hydrolysis of carbaryl in the presence of cationic surfactants
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2016
DOI: 10.17077/etd.3m1xfats
Abstract
<p>Alkaline degradation of Carbaryl in the presence of CTAB micelles has been reported as the most efficient method; however, the factors accounting for it are not yet clear. The main objective of this work was to study some of the factors affecting the alkaline degradation of Carbaryl in the presence of cetyl trimethylammonium bromide (CTAB). Three specific aims were researched in order to address the main objective.</p>
<p>Solubility studies, UV-vis, fluorescence, and 1D-HNMR and 2D-HNMR spectroscopies were used to research the solubilization of carbaryl in CTAB micelles. Solubility studies showed that carbaryl partitions into CTAB micelles with a binding constant of 553 ± 8 M-1, and each mole of micellized surfactant incorporates about 0.336 moles of carbaryl. Spectroscopy studies showed that carbaryl does not interact electrostatically with micelles but does through van der Waals interactions. 1D-HNMR and 2D-HNMR indicated solubilization in the Stern layer, oriented with its hydrophilic moiety towards the Goüy-Chapman layer and the hydrophobic moiety towards the core of the micelle.</p>
<p>Kinetic studies as a function of the surfactant concentration along with micellar kinetic models were used to calculate micellar rate constants (k’M) for each of four different cationic surfactants: cetyl trimethylammonium hydroxide (CTAOH), cetyl trimethylammonium bromide (CTAB), cetyl trimethylammonium chloride (CTACl), and cetyl pyridinium chloride (CPCl), and compared to the corresponding rate constants (k’W) in water; the results in all cases showed k’M / k’W > 1. This fact led to the conclusion that additional factors beyond solubilization of substrates are playing a role. Solubility studies revealed the following binding constant order and solubilization capacity order: CPCl > CTAOH ≈ CTAB > CTACl, CPCl > CTAOH ≈ CTAC > CTAB, indicating that for CPCl, Coulombic interactions, such as charge-transfer complexes, may be favoring the concentration effects, while for other surfactants, such as CTAOH, the [–OH] as the micelle counterion increases Carbaryl’s concentration in the Stern layer compared to its bulk concentration. In contrast, large, weakly-hydrated polarizable ions such as Br– displace hydrophilic ions, providing less enhancement.</p>
<p>Kinetic experiments as a function of the surfactant head’s charge led to the conclusion that cationic and zwitterionic surfactants have a catalytic effect of the alkaline hydrolysis of carbaryl, while nonionic and anionic surfactants have inhibitory effects: kobs (cationic) > kobs (zwitterionic) > kobs(nonionic) > kobs (anionic). A similar order for solubility parameters (Ks and SC) was observed from equilibrium solubility studies. Experiments as a function of the polarity of the medium in the presence of both polar and nonpolar solvents showed that the hydrolysis rate is inversely proportional to the medium polarity. Ionic strength experiments showed that the hydrolysis rate is inversely proportional to the ion concentration.</p>
Details
- Title: Subtitle
- Factors affecting the alkaline hydrolysis of carbaryl in the presence of cationic surfactants
- Creators
- Carlos Arturo Peroza Meza - University of Iowa
- Contributors
- Dale Eric Wurster (Advisor)Maureen D. Donovan (Committee Member)Lee E. Kirsch (Committee Member)Lewis L. Stevens (Committee Member)Mickey L. Wells (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Pharmacy (Pharmaceutics)
- Date degree season
- Spring 2016
- DOI
- 10.17077/etd.3m1xfats
- Publisher
- University of Iowa
- Number of pages
- xx, 298 pages
- Copyright
- Copyright © 2016 Carlos Arturo Peroza Meza
- Language
- English
- Date submitted
- 08/29/2018
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references (pages 290-298).
- Public Abstract (ETD)
The accumulation of n-methyl carbamate insecticides such as carbaryl in surface water is posing both environmental and human threats. Out of several methodologies explored to degrade it, micellar catalysis, particularly in alkaline conditions and in the presence of cetyl trimethylammonium bromide (CTAB) micelles, is the most effective. However, some of the factors that make CTAB micelles effective in catalyzing this reaction have not been studied previously.
One of the factors was found to be the solubilization site of carbaryl in CTAB micelles. Carbaryl most likely resides in the Stern layer of the CTAB micelle structure just between a water-like (polar) region and an oil-like (apolar) region oriented with its water-like moiety towards the water-like part of the micelles and the oil-like moiety towards the center or core of the micelle.
Mathematical models were used to help further explain the reaction and to calculate parameters such as micellar reaction-rate constant (k’M). A comparison of the micellar reaction-rate constant to the rate constant (k’M) in water led to the conclusion that other factors beyond solubilization of the substrate are playing a role.
Experiments as a function of the surfactant head group’s charge revealed that even though carbaryl is solubilized in cationic, anionic, zwiterionic, and nonionic surfactants, the reaction is catalyzed in cationic and zwiterionic surfactants and inhibited in nonionic and anionic surfactants. The following order of activity towards the reaction was found: cationic > zwiterionic > nonionic > anionic.
- Academic Unit
- Pharmacy
- Record Identifier
- 9983777379902771
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