Safe and Fast Flow Synthesis of Functionalized Oxazoles with Molecular Oxygen in a Microstructured Reactor

Abstract

The synthesis of hydroperoxymethyl oxazoles by oxidation of alkylideneoxazoles with molecular oxygen was implemented in a microstructured reactor for increased safety and larger-scale applications. Elaborate studies on the influence of pressure and temperature were performed, and the apparent activation energy for the oxidation reaction was determined.Elevated temperatures up to 100 °C and pressures up to 18 bar(a) led to a conversion rate of approximately 90 % within 4 h of the reaction time, thus displaying the high potential and beneficial effect of using a microreactor setup with liquid recycle loop for this oxidation. The in situ reduction of the generated hydroperoxide functionality shows the capability of this setup for follow-up transformations.

Supported Gold Nanoparticles as Reusable Catalysts for Oxidation Reactions of Industrial Significance

“…Tests were performed at 100 °C under 4 bar O 2 in a base‐free system. However, the use of O 2 should be undertaken with proper safety precautions …”

Gold‐Catalyzed Transformations of Propargyl Alcohols and Propargyl Amines

“…Very interestingly, in 2012 Hashmi and co‐workers found that the 5‐methylene‐4,5‐dihydrooxazole intermediate I could undergo an autoxidation to hydroperoxymethyl oxazole 118 , which could conveniently be converted to the corresponding alcohols by reduction with sodium borohydride (Scheme ) . In 2016, Hashmi and Röder achieved the safe and fast Flow synthesis of hydroperoxymethyl oxazoles …”

Commercial Gold(I) and Gold(III) Compounds Supported on Carbon Materials as Greener Catalysts for the Oxidation of Alkanes and Alcohols

“…Homogeneous gold catalysts (in the form of soluble complexes) can have high activity, enantioselectivity, and well‐characterized structures, but heterogeneous gold systems show longer lifetimes, easier separation of the catalyst from the products, possible catalyst recycling, and adaptation to continuous flow processes (for the problems with continuous‐flow processes in homogeneous gold catalysis, see Ref. ). Thus, the possibility to combine the remarkable properties of homogeneous catalysts with the well‐known advantages of heterogeneous systems by anchoring soluble gold complexes on solid supports is a very promising interface area of research…”