Aerobic oxidations in flow: opportunities for the fine chemicals and pharmaceuticals industries

Abstract

Molecular oxygen is without doubt the greenest oxidant for redox reactions, yet aerobic oxidation is one of the most challenging to perform with good chemoselectivity, particularly on an industrial scale. This collaborative review (between teams of chemists and chemical engineers) describes the current scientific and operational hurdles that prevent the utilisation of these reactions for the production of speciality chemicals and active pharmaceutical ingredients (APIs). The safety aspects of these reactions are discussed, followed by an overview of (continuous flow) reactors suitable for aerobic oxidation reactions that can be applied on scale. Some examples of how these reactions are currently performed in the industrial laboratory (in batch and in flow) are presented, with particular focus on the scale-up strategy. Last but not least, further challenges and future perspectives are presented in the concluding remarks

Catalytic Transformation of Biomass Derivatives to Value‐Added Chemicals and Fuels in Continuous Flow Microreactors

“…[144][145][146][147]149] The benefits of performing (aerobic) oxidation reactions in microreactors (of non-biomass derivatives) has been reviewed by multiple groups. [262][263][264] Heterogeneously catalyzed oxidation reactions have been shown to benefit from microreactor operation as compared to larger scale flow reactors. Both wallcoated [275] and packed bed microreactor configurations [183,276,277] have been used for this purpose.…”

Sol–gel Entrapped Nitroxyl Radicals: Catalysts of Broad Scope

“…In general, for heterogeneous catalysts to be actually used in flow reactors, the catalytic materials need to meet two main requirements, namely broad reaction scope and prolonged stability. Mesoporous and mechanically strong glassy silica‐based powdered materials functionalized with TEMPO‐like radicals are ideally suited for use in such reactors being easily packed in the tubular reactors in which they retain their structure and morphology for prolonged time owing to their high mechanical and thermal stability.…”

Catalytic Aerobic Oxidation of C(sp3)−H Bonds

“…Furthermore,b ulk chemicals are typically very simple molecules which avoid chemoselectivity issues,a nd the sheer volume of oxidant needed for their transformation makes O 2 the only economically viable candidate.According to UllmannsE ncyclopedia of Industrial Chemistry,t he limit above which O 2 economically outperforms other oxidants such as HNO 3 ,H 2 SO 4 and SO 3 /H 2 SO 4 (oleum), Cl 2 ,M nO 2 , CrO 3 ,a nd H 2 O 2 currently lies between 10 4 -10 5 tonnes per annum (t/a) depending on the product. [7] The majority concern the oxidation of C(sp 3 ) À Hb onds (49 examples) (C(sp 2 ) À Ho nly 8e xamples). [7] The majority concern the oxidation of C(sp 3 ) À Hb onds (49 examples) (C(sp 2 ) À Ho nly 8e xamples).…”