“…O 2 was generated from the high temperature decomposition of H 2 O 2 in a pre-mixer. Subsequently, the same group reported the identification of improved catalyst systems for the reaction [129]. Nonetheless, the high critical point of H 2 O makes the use of scH 2 O less synthetically relevant for pharmaceutical applications.Scheme 30Continuous flow oxidation of para-xylene to terephthalic acid in supercritical H 2 O…”
Molecular oxygen (O2) is the ultimate “green” oxidant for organic synthesis. There has been recent intensive research within the synthetic community to develop new selective liquid phase aerobic oxidation methodologies as a response to the necessity to reduce the environmental impact of chemical synthesis and manufacture. Green and sustainable chemical processes rely not only on effective chemistry but also on the implementation of reactor technologies that enhance reaction performance and overall safety. Continuous flow reactors have facilitated safer and more efficient utilization of O2, whilst enabling protocols to be scalable. In this article, we discuss recent advancements in the utilization of continuous processing for aerobic oxidations. The translation of aerobic oxidation from batch protocols to continuous flow processes, including process intensification (high T/p), is examined. The use of “synthetic air”, typically consisting of less than 10% O2 in N2, is compared to pure O2 (100% O2) as an oxidant source in terms of process efficiency and safety. Examples of homogeneous catalysis and heterogeneous (packed bed) catalysis are provided. The application of flow photoreactors for the in situ formation of singlet oxygen (1O2) for use in organic reactions, as well as the implementation of membrane technologies, green solvents and recent reactor solutions for handling O2 are covered.
“…O 2 was generated from the high temperature decomposition of H 2 O 2 in a pre-mixer. Subsequently, the same group reported the identification of improved catalyst systems for the reaction [129]. Nonetheless, the high critical point of H 2 O makes the use of scH 2 O less synthetically relevant for pharmaceutical applications.Scheme 30Continuous flow oxidation of para-xylene to terephthalic acid in supercritical H 2 O…”
Molecular oxygen (O2) is the ultimate “green” oxidant for organic synthesis. There has been recent intensive research within the synthetic community to develop new selective liquid phase aerobic oxidation methodologies as a response to the necessity to reduce the environmental impact of chemical synthesis and manufacture. Green and sustainable chemical processes rely not only on effective chemistry but also on the implementation of reactor technologies that enhance reaction performance and overall safety. Continuous flow reactors have facilitated safer and more efficient utilization of O2, whilst enabling protocols to be scalable. In this article, we discuss recent advancements in the utilization of continuous processing for aerobic oxidations. The translation of aerobic oxidation from batch protocols to continuous flow processes, including process intensification (high T/p), is examined. The use of “synthetic air”, typically consisting of less than 10% O2 in N2, is compared to pure O2 (100% O2) as an oxidant source in terms of process efficiency and safety. Examples of homogeneous catalysis and heterogeneous (packed bed) catalysis are provided. The application of flow photoreactors for the in situ formation of singlet oxygen (1O2) for use in organic reactions, as well as the implementation of membrane technologies, green solvents and recent reactor solutions for handling O2 are covered.
“…to A could be invoked. F would be transformed into hydroperoxide intermediate C , further leading to HMLA 4 as mentioned above . Some authors reported for other substrates the possible formation of the alcohol G which could be acetylated to H and further oxidised to D by Br .…”
“…A synergistic effect between copper and other metals, such as cobalt, was found to enhance this reaction as exemplified by utilizing a four-component catalyst system (Cu/Co/NH 4 /Br). In this case subcritical water gave significantly better results than scH 2 O which was rationalized by a temperature-dependent equilibrium shift in the ammonium bromide decomposition [33].…”
Section: Oxidation Of Hydrocarbonsmentioning
confidence: 97%
“…Detailed mechanistic studies on the continuous oxidation of o-and p-xylene led to the discovery of another catalytic system using CuBr 2 in a selective oxidation process utilizing a similar flow setup [32,33]. A synergistic effect between copper and other metals, such as cobalt, was found to enhance this reaction as exemplified by utilizing a four-component catalyst system (Cu/Co/NH 4 /Br).…”
In recent years, the high demand for sustainable processes resulted in the development of highly attractive oxidation protocols utilizing molecular oxygen or even air instead of more uneconomic and often toxic reagents. The application of these sustainable, gaseous oxidants in conventional batch reactors is often associated with severe safety risks and process challenges especially on larger scales. Continuous flow technology offers the possibility to minimize these safety hazards and concurrently allows working in high-temperature/high-pressure regimes to access highly efficient oxidation protocols. This review article critically discusses recent literature examples of flow methodologies for selective aerobic oxidations of organic compounds. Several technologies and reactor designs for biphasic gas/liquid as well as supercritical reaction media are presented in detail.
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