Anthraquinone oxidation proces

In pulp and paper processing, anthraquinone (AQ) accelerates the delignification of wood and improves liquor selectivity. The kinetics of the liquid-phase oxidation of anthracene (AN) to AQ with NO2 in acetic acid as solvent has been studied by Rodriguez and Tijero (1989) in a semibatch reactor (batch with respect to the liquid phase), under conditions such that the kinetics of the overall gas-liquid process is controlled by the rate of the liquid-phase reaction. This reaction proceeds through the formation of the intermediate compound anthrone (ANT) ... 

This study indicates that the oxidation of dihydroanthracene in a basic medium involves the formation of a monocarbanion, which is then converted to a free radical by a one-electron transfer step. It is postulated that the free radical reacts with oxygen to form a peroxy free radical, which then attacks a hydrogen atom at the 10-position by an intramolecular reaction. The reaction then proceeds by a free-radical chain mechanism. This mechanism has been used as a basis for optimizing the yield of anthraquinone and minimizing the formation of anthracene. 

In this case the starting material is considerably more difficult to oxidize than the product under comparable conditions benzene is oxidized at a potential 1.3 V higher than phenol. Consequently, it is observed that the reaction usually cannot be stopped at the phenol stage, but proceeds to benzoquinone [14,15]. Similarly, the oxidation of 9,10-dihaloanthracenes leads to anthraquinone in an addition-elimination reaction [16]. However, the problem may to some extent be overcome if the degree of substrate conversion is kept low (e.g., the anodic oxidation of phenol to hydroquinone [17]) or if the oxidation product is continuously removed (e.g., the indirect oxidation of methylarenes... 

The direct bromination of -alkoxylactones at the p position initially generates the a. -unsaturated lactones (eq 14) however, the required radical abstraction is not so facile and further bronii-nation of the Q , -unsaturated lactone proceeds competitively to afford the mono- and dibrominated products. NBS is also used for the oxidative aromatization of polycyclic compounds, including steroids and anthraquinone precursors (eq 15). ... 

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