Cumene oxidation side reactions

The importance of the acid-catalyzed side reactions are illustrated in Table 3 by the product distribution obtained using either TBHP or cumene hydroperoxide (CHP) as oxidant. The epoxidation with TBHP is faster and considerably more selective. When using CHP, about 20 mol% of the coproduct 2-phenyl-2-propanol was dehydrated to a-methylstyrene. It is likely that the simultaneously formed water increases the (Brpnsted) acidity of the aerogel and thus accelerates the ring opening and - to a smaller extent - the isomerization reactions. No oxidation products were formed in the absence of peroxide, as expected. Slow isomerization from p- to a-isophorone catalyzed by titania-silica was the only reaction observed. The data in Table 3 indicate that the simultaneous presence of peroxide and catalyst in the reaction mixture markedly accelerates the acid-catalyzed isomerization reaction. 

The cumene feed must be free of oxidation propagation chain splitters, especially sulfur compounds, styrene, aniline and phenol. Since the reaction rate is extremely sensitive to these impurities, special care is taken to remove them. Phenol can be removed by treatment with caustic soda. However, its effect is less harmful than it appears, because it exerts an even more inhibitory action on side reactions, leading for instance to acetophenone or 2-phenyl 2-propanol, than on the main hydroperoxidation reaction, and because, in small amounts (10 to 1000 ppm), and combined with the sodium salt of cumyl hydroperoxide, its effect enhances tbe final yield ofthe operation. 

Figure 2.2 Important side reactions in the cumene oxidation.

Three patents issued in 1924 and 1925 are conspicuous as placing special emphasis upon the preparation of particular catalysts as suitable for reactions involving the partial oxidation of side chains present in aromatic nuclei. The first00 of these relates to the oxidation of aromatic hydrocarbons and their derivatives, viz., toluene, xylene, cymene, cumene, mesitylene, cresols, etc., together with their derivatives including nitro-... 

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