TY  - THES
AB  - The reaction kinetics of the alkylation of the enolate of 2-benzylindane-1,3-dion (BzInd-) with benzylbromide (BzBr) in surfactant containing aqueous and micellar solutions and in microemulsions was investigated. The kinetics of the main side reactions, the solvolysis of BzBr, was included.
To explore the range of suitable microemulsion formulations, the influence of reactand concentrations and temperature on the stability of microemulsions with the nonionic surfactant Igepal CO-520 and heptane was investigated by turbidity and conductometric measurements. The additives (reactands) make the stability range of the microemulsion shift to notable lower temperatures. For the solubility of BzBr in micelles of polyether surfactants marked temperature optima exist, which must be recognized for the choice of a suitable surfactant for a desired application.
The rates of the reactions BzBr + X- ----> BzX + Br- (with the nucleophiles X- = H2O, OH-, BzInd-) were measured by spectrophotometry, potentiometry or conductometry. Results were quantitatively described by the pseudophase ion exchange model (PPIEM), whereby rate constants in the three pseudophases (aqueous bulk, interfacial, oily domains) and partition coefficients of the reactants between the pseudophases were fitted.
The rate constants in the aqueous pseudophase were extrapolated from overall rate constants in solutions containing surfactants below the cmc. With these and overall rate coefficients in micellar solutions (without oily pseudophase) the rate coefficients in the surfactant pseudophase and partition coefficients between aqueous and surfactant pseudophases were obtained.
From kinetic measurements of the BzBr solvolysis as a function of the BzBr concentration at constant surfactant concentration, it could be concluded that BzBr is predominantly distributed in the micellar periphery and does not form droplets inside the micelles. However, if exist oily droplets inside the micelles of a microemulsion, the BzBr concentration in the oily pseudophase is three times larger than in the surfactant pseudophase.
A comparison of the reactivity of the BzBr with the nucleophiles water (uncharged and hydrophilic), hydroxide (charged and hydrophilic) and enolate carbanion (charged and amphiphilic) in the different systems reveals the influence of the microemulsion on the selectivity of SN2 reactions: when transfered from aqueous to micellar solution or to a microemulsion, the reaction with the amphiphilic BzInd- is favored against that with OH- by the factor 3 to 4, where the different partition coefficients are decisive.
This feature and the plot of phase stability management together show that microemulsions may be suitable media for reactions of this class. The influence of micellar charge and the different hydrophilicity resp. HLB of nonionic polyether surfactants on the micellar catalysis was also investigated and discussed.
DA  - 1996
KW  - Mikroemulsion , Benzylbromid , Nucleophile Reaktion , Reaktionskinetik , Pseudophase , Mizellare Katalyse , Nukleophil , Phasengleichgewicht , Verteilungskoeffizient , Microemulsion , Pseudophase , Micellar catalysis
LA  - ger
PY  - 1996
TI  - Kinetik nukleophiler Reaktionen mit Benzylbromid in Mikroemulsionen
UR  - https://nbn-resolving.org/urn:nbn:de:hbz:361-5853
Y2  - 2024-11-25T05:03:02
ER  -