8 research outputs found
Diastereoselectivity in Chiral Ruthenium Complexes of Bidentate Bisphosphine Monoxide Ligands:Â Controlling Epimerization in Aldehyde Complexes and 16-Electron Intermediates
A General Kinetic Theory of Rate Enhancements for Reactions between Organic Substrates and Hydrophilic Ions in Micellar Systems
JORNADAS 65 ANIVERSARIO DE LA ESCUELA DE GEOLOGĂA, MINAS Y GEOFĂSICA, UNIVERSIDAD CENTRAL DE VENEZUELA, CARACAS, NOVIEMBRE 2002
JORNADAS 65 ANIVERSARIO DE LA ESCUELA DE GEOLOGÍA,MINAS Y GEOFÍSICA, UNIVERSIDAD CENTRAL DE VENEZUELA,CARACAS, NOVIEMBRE 200
The Nature of the Sodium Dodecylsulfate Micellar Pseudophase as Studied by Reaction Kinetics
The nature of the rate-retarding effects of anionic micelles of sodium dodecyl sulfate (SDS) on the water-catalyzed hydrolysis of a series of substituted 1-benzoyl-1,2,4-triazoles (1aâf) has been studied. We show that medium effects in the micellar Stern region of SDS can be reproduced by simple aqueous model solutions containing small-molecule mimics for the surfactant headgroups and tails, namely sodium methyl sulfate (NMS) and 1-propanol, in line with our previous kinetic studies for cationic surfactants (Buurma et al. J. Org. Chem. 2004, 69, 3899â3906). We have improved our mathematical description leading to the model solution, which has made the identification of appropriate model solutions more efficient. For the Stern region of SDS, the model solution consists of a mixture of 35.3 mol dmâ3 H2O, corresponding to an effective water concentration of 37.0 mol dmâ3, 3.5 mol dmâ3 sodium methylsulfate (NMS) mimicking the SDS headgroups, and 1.8 mol dmâ3 1-propanol mimicking the backfolding hydrophobic tails. This model solution quantitatively reproduces the rate-retarding effects of SDS micelles found for the hydrolytic probes 1aâf. In addition, the model solution accurately predicts the micropolarity of the micellar Stern region as reported by the ET(30) solvatochromic probe. The model solution also allows the separation of the individual contributions of local water concentration (water activity), polarity and hydrophobic interactions, ionic strength and ionic interactions, and local charge to the observed local medium effects. For all of our hydrolytic probes, the dominant rate-retarding effect is caused by interactions with the surfactant headgroups, whereas the local polarity as reported by the solvatochromic ET(30) probe and the Hammett Ï value for hydrolysis of 1aâf in the Stern region of SDS micelles is mainly the result of interactions with the hydrophobic surfactant tails. Our results indicate that both a mimic for the surfactant tails (NMS) and a mimic for the surfactant headgroups (1-propanol) are required in a model solution for the micellar pseudophase to reproduce all medium effects experienced by a variety of different probes
Memorias IX Congreso GeolĂłgico Venezolano (1)
Memorias del IX Congreso Geológico Venezolan