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2001
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In the Laboratory
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Micellar Effects on the Spontaneous Hydrolysis of Phenyl Chloroformate. A Kinetic Experiment for the Physical Chemistry Laboratory
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Juan Crugeiras, J. Ramón Leis, and Ana Ríos
Departamento de Química Física, Facultad de Química, Universidad de Santiago de Compostela, Avda. de las Ciencias s/n, 15706 Santiago de Compostela, Spain
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November 2001
Vol. 78 No. 11
p. 1538
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| Abstract |
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This undergraduate laboratory experiment has been designed to help students understand the main features of micellar aggregates and how these organized structures may influence the rates of kinetically simple reactions. It describes the effect of sodium dodecyl sulfate micelles on the spontaneous hydrolysis of phenyl chloroformate. Experimental values of the first-order rate constant for this reaction in the absence and in the presence of surfactant are determined by following (i) the formation of phenol, by UV spectroscopy, and (ii) the formation of HCl, by conductivity measurements. The reaction is strongly inhibited by the presence of micelles and the observed micellar effects are quantitatively analyzed in terms of the pseudophase model. This analysis allows the evaluation of the binding constant of the substrate to the micelles, Ks, and of the rate constant for the reaction in the micellar pseudophase, km. The observed difference between the rate constant in water, kw, and that in the presence of micellized surfactant, km, is explained in terms of the mechanism of the reaction and the properties of the microenvironment provided by the micelles.
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| Supplement |
Notes for the instructor and detailed instructions for students are available.
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 Contents |
JCE2001p1538W.doc (Microsoft Word)
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| More Information |
Citation |
Crugeiras, Juan; Leis, J. Ramón; Ríos, Ana. J. Chem. Educ. 2001 78 1538.
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Keywords |
Kinetics; Laboratory Instruction; Micelles; Physical Chemistry; UV-Vis Spectroscopy
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History |
Created:
Last Updated: |
October 8, 2001
August 31, 2005
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| Home > JCE Print > Journal of Chemical Education > Issues >
2001
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November
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1538
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