Anthraquinone autoxidation step

In the autoxidation step of the AO process, the 2H /2e reduction of O2 to HjOj is coupled to the uncatalyzed oxidation of anthrahydroquinone to anthraquinone. A variety of 2-alkylanthraquinones have been reported, but 2-ethylanthraquinone... 

An important redox equilibrium exists between anthrahydroquinone A and tetra (Eq. (14.9)). Because tetra is more readily reduced than the parent anthraquinone, this equilibrium lies almost entirely to the right. Thus, if tetra formation is not suppressed, eventually all the hydroquinone species present in the oxidation process will consist of the reduced form of tetra. Because the analogous tetra hydroquinone is oxidized more slowly, the autoxidation step will slow down significantly. 

The autoxidation mechanism by which 9,10-dihydroanthra-cene is converted to anthraquinone and anthracene in a basic medium was studied. Pyridine was the solvent, and benzyl-trimethylammonium hydroxide was the catalyst. The effects of temperature, base concentration, solvent system, and oxygen concentration were determined. A carbanion-initi-ated free-radical chain mechanism that involves a singleelectron transfer from the carbanion to oxygen is outlined. An intramolecular hydrogen abstraction step is proposed that appears to be more consistent with experimental observations than previously reported mechanisms that had postulated anthrone as an intermediate in the oxidation. Oxidations of several other compounds that are structurally related to 9,10-dihydroanthracene are also reported. 

Hydrogen peroxide is mostly produced on a large scale using the anthraquinone (AQ) autoxidation process. The key step is the selective liquid-phase hydrogenation of the AQs to their corresponding hydroquinones (Scheme 9.8). An industrial process has been designed at Chalmers University and developed and used by Akzo-Nobel on the pilot scale. It involves a three-phase monolith reactor but very few details... 

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