Hydroxylation of Alkanes and Benzene Derivatives

Selective oxidation of alkanes and benzene derivatives to alcohols and phenols, respectively, are among the most difficult reactions in oxidation catalysis. Therefore, the stoichiometric hydroxylation of alkenes and aromatics performed by a-oxygen at room temperature has aroused great interest as a potential way for developing new steady state catalytic processes for the preparation of these valuable products, similar to the hydroxylation of benzene to phenol. 

The catalytic hydroxylation of methane [39, 95], ethane [136, 137], propane [138-141], cyclohexane [68] and cyclododecane [142] has been tested using the Fe-contain-ing zeolites. In most cases the selectivity was low or even zero. With ethane and propane, instead of their hydroxylation to alcohols, oxidehydrogenation (ODH) takes place, yielding ethylene and propylene, respectively, in yields of up to 25-30%. According to Bulanek et al. [140] the ODH of propane proceeds via intermediate formation of propanol, which further is subjected to dehydration. 

The hydroxylation of benzene derivatives proceeds much more selectively. Table 7.7 presents the main published results. With some substrates like chloroben- 

Substrate Temperature (K) Substrate conversion ( ) Selectivity to hydroxylated products (%) Reference 

With alkylaromatics, Costine et al. [146] observed a competition effect between the aromatic and aliphatic attack of the N20 that was influenced by the steric and electronic factors. A similar effect has been observed by Rodkin et al. [121] for the stoichiometric hydroxylation of alkylaromatics by a-oxygen at room temperature. 

The hydroxylation of benzene derivatives proceeds much more selectively. 

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Catalytic Oxidation by Nitrous Oxide in the Cas Phase 229 7.3.2.5 Hydroxylation of Alkanes and Benzene Derivatives... 

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