Practical process for the air oxidation of cresols: Part B. evaluation of the laboratory-scale oxidation process
Organic Process Research and Development
Catalysis Research Unit, Faculty of Applied Science, Port Elizabeth Technikon, Private Bag X6011, Port Elizabeth 6000, South Africa
Mechanistic proposals and predictions made in a preceding paper (Part A) were evaluated by carrying out the catalytic air oxidation of p-cresol in an alternative solvent system, comprising either a mixture of ethylene glycol and acetic acid (for oxidations under acidic conditions) or ethylene glycol and water (for oxidations under basic conditions). The results obtained in these experiments confirmed that ethylene glycol acts as a nucleophile in these solvent systems, thereby stabilizing the quinomethide intermediate and resulting in highly efficient oxidations in both alkaline and acidic media. 4-Hydroxybenzaldehyde, the desired product, was thus obtained in isolated yields of up to 98% and purities >99%. The inherent draw-backs associated with alkaline methanol and aqueous acetic acid solutions were thus circumvented, and the result is a highly efficient process for the production of 4-hydroxybenzaldehyde.
acetic acid; cresol; ethylene glycol; quinone derivative; water; acidity; alkalinity; article; catalysis; chemical reaction; molecular mechanics; molecular stability; oxidation kinetics; prediction; reaction analysis; scale up