Naphthalene heterogeneous oxidation

Heterogeneous oxidative processes operate at high temperatures (250-450 6C) and are useful for the synthesis of acrolein and acrylic acid from propylene over bismuth molybdate catalysts, the synthesis of maleic and phthalic anhydrides from the oxidation of benzene (or C4 compounds) and naphthalene (or o-xylene) respectively over vanadium oxide,101 arid the synthesis of ethylene oxide from ethylene over silver catalysts.102... 

Attenlion should be drawn to ihe use of tin oxide systems as heterogeneous catalysts. The oldest and mosi extensively patented systems are the mixed lin-vanadium oxide catalysis for the oxidation of aromatic compounds such as benzene, toluene, xylenes and naphthalene in the. synthesis of organic acids and acid anhydride.s. More recenily mixed lin-aniimony oxides have been applied lo the selective oxidaiion and ammoxidaiion of propylene to acrolein, acrylic acid and acrylonilrile. 

Heterogeneous catalysts activate C—H bonds at significantly higher temperatures. For example, a Fe/Co modified Mo-supported acidic ZSM-5 zeolite catalyst dehydrogenates methane under non-oxidizing conditions at 700°C to a mixture of Q-C4 alkanes/alkenes and Q-Q2 aromatics such as benzene and naphthalene.140... 

A more complicated but also very instructive and versatile process was published by Hydro Quebec, namely, the indirect oxidation of aromatics, specifically naphthalene, by ceric salts [9]. The electrolysis is only a small part of the process Cerous methanesulfonate is oxidized to ceric methanesulfonate. The organic part of the process takes place in a separate reactor The aqueous ceric salt oxidizes the organic substrate in a heterogeneous two-phase reaction that requires good mixing. After the separation of the aqueous and organic phases, the aqueous phase is extracted with a solvent that is recycled continuously. In a follow-up step, organic impurities must be removed from the cerous solution before it is fed back to the electrolysis. The product (naphthoquinone) has to be dried. 

The catalytic properties of V-HMS were investigated in detail by Reddy et al. [44], Naphthalene and 2-methylnaphthalene were oxidized at the 1,4-positions to afford the related 1,4-naphthoquinones. Under analogous conditions, 2,6-DTBP (83 % conv.) led to the corresponding p-quinone (87 %) and p-diphenoqui-none (4 %). The relative role of homogeneous and heterogeneous pathways in catalysis remained uncertain, because different amounts of V ions were released into the liquid phase under different conditions. 

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