Kinetic Study in Water−Ethylene Glycol Cationic, Zwitterionic, Nonionic, and Anionic Micellar Solutions

Abstract

The spontaneous hydrolysis of phenyl chloroformate was studied in water-ethylene glycol, EG, cationic, zwitterionic, nonionic, and anionic micellar solutions, the surfactants being tetradecyltrimethylammonium bromide, tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate, tricosaoxyethylene glycol ether, and sodium dodecyl sulfate. The dependence of the observed rate constant on surfactant concentration as well as on the percentage by weight of EG, varying from 0 to 50 wt %, was investigated. Information about changes in the critical micelle concentrations, in the micellar ionization degrees (for ionic surfactants), in the aggregation numbers, and in the polarity of the interfacial region of the micelles upon changing the weight percent of EG was obtained through conductivity, surface tension, spectroscopic, and fluorescence measurements. A simple pseudophase model was adequate to rationalize the kinetic data. Micellar medium effects were explained by considering charge-charge interactions and polarity, ionic strength, and water content in the micellar interfacial region. The acceleration of the reaction produced by an increase in the amount of EG present in the mixture was explained on the basis of the substantial decrease in the equilibrium binding constant of phenyl chloroformate molecules to the micelles, resulting in the contribution of the reaction taking place in the bulk water-EG phase being more important. The weight percent of EG did not substantially influence the rate constant in the micellar pseudophase.

Water−Ethylene Glycol Cationic Dimeric Micellar Solutions: Aggregation, Micellar Growth, and Characteristics As Reaction Media

“…One can see that the agreement between the experimental and the theoretical data is good. This agreement has been found, by different research groups, − ,,,,,− for the reaction MNBS + Br − in several micellar reaction media for which no morphological transitions occurred. Dashed lines in Figure show the expected dependence of k obs on [12-s-12,2Br − ] for the water−EG dimeric micellar solutions investigated if no substantial changes in the size and shape of micelles take place.…”

Water−Ethylene Glycol Cationic Dimeric Micellar Solutions: Aggregation, Micellar Growth, and Characteristics As Reaction Media

“…One can see that the agreement between the experimental and the theoretical data is good. This agreement has been found, by different research groups, − ,,,,,− for the reaction MNBS + Br − in several micellar reaction media for which no morphological transitions occurred. Dashed lines in Figure show the expected dependence of k obs on [12-s-12,2Br − ] for the water−EG dimeric micellar solutions investigated if no substantial changes in the size and shape of micelles take place.…”

Effects of Ethylene Glycol Addition on the Aggregation and Micellar Growth of Gemini Surfactants

“…Table shows that Reichardt's parameter increases as the wt % EG increases for all surfactant concentrations investigated. This result was also found for conventional surfactants in water−organic solvent mixtures, including DTAB. ,,− An increase in E T indicates an increase in the polarity of the micelles interfacial region and is in agreement with the decrease in N agg upon increasing wt % EG shown in Table . When micelles become smaller, less packed, the penetration of solvent molecules in the palisade layer is easier and an increase in the solvent interfacial concentration would be expected, increasing the polarity of this region.…”

“…These results point out that changes in the magnitude of the Gibbs energy contribution associated with the transfer of the dodecyl chains from the bulk phase into the micellar interior are the main factor controlling the value of Δ G ° M as well as its variations upon changing wt % EG . The same result was also found for a variety of conventional surfactants when polar organic solvents were added to the aqueous surfactants solutions. ,− …”

Water−N,N-Dimethylformamide Alkyltrimethylammonium Bromide Micellar Solutions: Thermodynamic, Structural, and Kinetic Studies

“…That is, the bulk−micelle interface region becomes more polar when the weight percent of DMF increases from 0 to 20. The same dependence of the polarity of the bulk−micelle interface region on the weight percent of organic solvent was found for water−ethylene glycol CTAB, TTAB, and DTAB micellar solutions 18 as well as for water−ethylene glycol SDS, Brij 35 , and SB3-14 micellar solutions . This increase in polarity could be related to the decrease in the aggregation number of the micellar aggregates when the amount of organic solvent present in the solution increases.…”

Water−Ethylene Glycol Cationic Dimeric Micellar Solutions: Aggregation, Micellar Growth, and Characteristics As Reaction Media

“…One can see that the agreement between the experimental and the theoretical data is good. This agreement has been found, by different research groups, − ,,,,,− for the reaction MNBS + Br − in several micellar reaction media for which no morphological transitions occurred. Dashed lines in Figure show the expected dependence of k obs on [12-s-12,2Br − ] for the water−EG dimeric micellar solutions investigated if no substantial changes in the size and shape of micelles take place.…”

Effects of Ethylene Glycol Addition on the Aggregation and Micellar Growth of Gemini Surfactants

“…Table shows that Reichardt's parameter increases as the wt % EG increases for all surfactant concentrations investigated. This result was also found for conventional surfactants in water−organic solvent mixtures, including DTAB. ,,− An increase in E T indicates an increase in the polarity of the micelles interfacial region and is in agreement with the decrease in N agg upon increasing wt % EG shown in Table . When micelles become smaller, less packed, the penetration of solvent molecules in the palisade layer is easier and an increase in the solvent interfacial concentration would be expected, increasing the polarity of this region.…”

“…These results point out that changes in the magnitude of the Gibbs energy contribution associated with the transfer of the dodecyl chains from the bulk phase into the micellar interior are the main factor controlling the value of Δ G ° M as well as its variations upon changing wt % EG . The same result was also found for a variety of conventional surfactants when polar organic solvents were added to the aqueous surfactants solutions. ,− …”

Water−N,N-Dimethylformamide Alkyltrimethylammonium Bromide Micellar Solutions: Thermodynamic, Structural, and Kinetic Studies

“…That is, the bulk−micelle interface region becomes more polar when the weight percent of DMF increases from 0 to 20. The same dependence of the polarity of the bulk−micelle interface region on the weight percent of organic solvent was found for water−ethylene glycol CTAB, TTAB, and DTAB micellar solutions 18 as well as for water−ethylene glycol SDS, Brij 35 , and SB3-14 micellar solutions . This increase in polarity could be related to the decrease in the aggregation number of the micellar aggregates when the amount of organic solvent present in the solution increases.…”

Water−Ethylene Glycol Cationic Dimeric Micellar Solutions: Aggregation, Micellar Growth, and Characteristics As Reaction Media

“…One can see that the agreement between the experimental and the theoretical data is good. This agreement has been found, by different research groups, − ,,,,,− for the reaction MNBS + Br − in several micellar reaction media for which no morphological transitions occurred. Dashed lines in Figure show the expected dependence of k obs on [12-s-12,2Br − ] for the water−EG dimeric micellar solutions investigated if no substantial changes in the size and shape of micelles take place.…”

Effects of Ethylene Glycol Addition on the Aggregation and Micellar Growth of Gemini Surfactants

“…Table shows that Reichardt's parameter increases as the wt % EG increases for all surfactant concentrations investigated. This result was also found for conventional surfactants in water−organic solvent mixtures, including DTAB. ,,− An increase in E T indicates an increase in the polarity of the micelles interfacial region and is in agreement with the decrease in N agg upon increasing wt % EG shown in Table . When micelles become smaller, less packed, the penetration of solvent molecules in the palisade layer is easier and an increase in the solvent interfacial concentration would be expected, increasing the polarity of this region.…”

“…These results point out that changes in the magnitude of the Gibbs energy contribution associated with the transfer of the dodecyl chains from the bulk phase into the micellar interior are the main factor controlling the value of Δ G ° M as well as its variations upon changing wt % EG . The same result was also found for a variety of conventional surfactants when polar organic solvents were added to the aqueous surfactants solutions. ,− …”

Water−N,N-Dimethylformamide Alkyltrimethylammonium Bromide Micellar Solutions: Thermodynamic, Structural, and Kinetic Studies

“…That is, the bulk−micelle interface region becomes more polar when the weight percent of DMF increases from 0 to 20. The same dependence of the polarity of the bulk−micelle interface region on the weight percent of organic solvent was found for water−ethylene glycol CTAB, TTAB, and DTAB micellar solutions 18 as well as for water−ethylene glycol SDS, Brij 35 , and SB3-14 micellar solutions . This increase in polarity could be related to the decrease in the aggregation number of the micellar aggregates when the amount of organic solvent present in the solution increases.…”