In situ Synthese eines Amphiphils an der internen Grenzfläche UV-sensitiver Mikroemulsionen

Tim Schreiner, 2012

The synthesis of molecules by combination of hydrophilic and hydrophobic reactants is a well-known task in chemical reactions. To this end often expensive and mostly toxic solvents are used, or alternatively, a mixture of polar and non-polar solvents as macroemulsion in order to dissolve both reactants. In this case only a small internal surface between the polar and non-polar phase is given leading to small reaction rates. Microemulsions avoid this limitation due to an inherent enormously large interfacial area, which facilitates significantly higher reaction rates [1]. By observing the phase behavior of microemulsions the reaction progress and hence the kinetics is possible. To demonstrate this feature a photochemical induced [2+2]-cycloaddition (Paternò-Büchi reaction) in microemulsion was studied as model reaction. The product of the Paternò-Büchi reaction of pyruvic acid and 1?octene is 3?hexyl?2methyloxetane? 2?carboxylic acid, which is an amphiphile. As such it influences the phase behavior of the microemulsion system significantly. A variation of the UV?irradiation results in a shift of the point of the highest efficiency of the system to lower temperatures and an increase in efficiency. The influence of the new synthesized amphiphile is accordingly that of a hydrophobic co-surfactant. These results demonstrate the direct correlation between the change in phase behavior and reaction progress. In theoretical calculations the thermochemistry of the reaction was evaluated. A comparison of the enthalpies and free energies of educts and products indicates that an endothermic, as well as an endergonic reaction process is expected. Furthermore, the most stable stereoisomer was calculated in the SS conformation.

[1]       T. Wielputz, et al., Chem-Eur J 12 (29), 7565 (2006).