Abstract
This collaborative review (between teams of chemists and chemical engineers) describes the current scientific and operational hurdles that prevent the utilisation of aerobic oxidation reactions for the production of speciality chemicals and active pharmaceutical ingredients (APIs).
Highlights
Molecular oxygen (O2) is unquestionably the most important constituent of our planet's atmosphere
In this Review, we present the hazards and safety issues of aerobic oxidation reactions in the liquid phase using organic solvents, followed by a brief survey of the types of reactors that can be used
It is important to note that these limiting concentrations are linked to the process temperature and pressure: for each 100 °C increase, the lower flammable limits and the limiting oxygen concentration (LOC) at 1 atm decrease by about 8% of their values at near normal room temperature; the upper flammable limits increase by approximately 8% for the same conditions.[35]
Summary
Molecular oxygen (O2) is unquestionably the most important constituent of our planet's atmosphere. Bulk chemicals are simple molecules with few functional groups and low molecular weights/boiling points This allows some reactions to be performed in the gas-phase at elevated temperatures and pressures (e.g. oxidation of ethylene to ethylene oxide), which are not compatible with the synthesis of more complex organic molecules required by the fine chemicals and pharmaceutical industries. Aerobic oxidations fall into a unique category of reactions that cannot be performed in batch, due to the considerable headspace within the reactors To illustrate these differences, we shall consider the current industrial process used to produce terephthalic acid (TA), (6) (Scheme 4).[27] Contrary to many other petrochemical oxidation reactions, TA is produced industrially using an organic solvent (acetic acid), and may serve as a useful process to gain transferrable insight for the small scale processing of pharmaceuticals. Dilution of oxygen with inert gases to counteract this leads, in turn, to sub-stoichiometry and large reactor sizes
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