A new class of cationic surfactants containing the heterocyclic piperazinium ring in their covalent structure was prepared; cetyldialkylpiperazinium halides, CRPX, with alkyl = Me (CMPX), Et (CEPX), n-Pr (CPPX), and with halide = Br and Cl. They were characterized by measures of critical micellar concentration, cmc, and ionization degree, α, and also by use of the decarboxylation of 6-nitrobenzisoxazole-3-carboxylate as a kinetic probe to investigate the properties of the microinterface they provide in aqueous solutions. The pseudophase kinetic treatment fails to fit the data at high [surfactant], which show anomalies with abrupt increase in kobs, especially for CEPX and CPPX. Data can be fitted up to [surfactant] ca. 0.1 M, and 0.2 M in some cases. Compared with cetyltrialkylammonium halides, values of k'M indicate a water-richer microenvironment and less important interface property changes with increasing head group bulk. The reaction could be studied both in the presence and in the absence of NaOH; comparison shows that NaOH affects only the shape of the kinetic profile at low [surfactant], without affecting the microenvironment provided by mature micelles.

Decarboxylation of 6-nitrobenzisoxazole-3-carboxylate as Kinetic Probe for Piperazinium-based Cationic Micelles

BRINCHI, Lucia;GERMANI, Raimondo;SAVELLI, Gianfranco;
2004

Abstract

A new class of cationic surfactants containing the heterocyclic piperazinium ring in their covalent structure was prepared; cetyldialkylpiperazinium halides, CRPX, with alkyl = Me (CMPX), Et (CEPX), n-Pr (CPPX), and with halide = Br and Cl. They were characterized by measures of critical micellar concentration, cmc, and ionization degree, α, and also by use of the decarboxylation of 6-nitrobenzisoxazole-3-carboxylate as a kinetic probe to investigate the properties of the microinterface they provide in aqueous solutions. The pseudophase kinetic treatment fails to fit the data at high [surfactant], which show anomalies with abrupt increase in kobs, especially for CEPX and CPPX. Data can be fitted up to [surfactant] ca. 0.1 M, and 0.2 M in some cases. Compared with cetyltrialkylammonium halides, values of k'M indicate a water-richer microenvironment and less important interface property changes with increasing head group bulk. The reaction could be studied both in the presence and in the absence of NaOH; comparison shows that NaOH affects only the shape of the kinetic profile at low [surfactant], without affecting the microenvironment provided by mature micelles.
2004
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11391/162034
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