Dramatic Enhancement of Enone Epoxidation Rates in Nonionic Microemulsions

✍ Scribed by Thomas Wielpütz; Thomas Sottmann; Reinhard Strey; Friederike Schmidt; Albrecht Berkessel

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 181 KB
• Volume: 12
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.200600550

✦ Synopsis

Abstract

The ability of microemulsions to dissolve polar and non‐polar components with a huge internal interface can overcome the reagent incompatibilities frequently encountered in organic reactions. We investigated model epoxidation reactions of α,β‐unsaturated enones and alkaline hydrogen peroxide in different nonionic microemulsions, both in the presence and absence of a phase‐transfer agent (PTA). The obtained reaction profiles were compared with those for the corresponding surfactant‐free two‐phase systems. In addition, we defined a time constant τ as a measure for the rate of turnover. The epoxidation of trans‐chalcone using an n‐alkyl‐polyoxyethylene surfactant based microemulsion was fastest in the system with the PTA (τ=66 min) and slightly slower without the PTA (τ=77 min). It was still slower in the two‐phase system with a PTA (τ=114 min) and extremely sluggish without a phase‐transfer agent. With n‐alkyl β‐D‐glucopyranoside as the surfactant the conversion was twice as fast than in the former microemulsion systems, but the PTA did not accelerate the reaction further (τ=35 and 33 min). The epoxidation of vitamin K~3~, the second model system, was extremely accelerated. It proceeded a factor of approximately 35 faster in the microemulsion (τ=1.44 min) than in the corresponding two‐phase system (τ=57 min).