Dehydrogenation and oxidation of heterocyclic compounds

Conjugated dehydrogenation of isopropylbenzene was planned [87] by the method of experiments with the minimal number of tests. Total yields of styrene and a-methylstyrene per injected isopropylbenzene were taken for optimized parameters, because these monomers are equally valuable. At the gradient motion (T = 640 °C) the highest yield of the target products (styrene + a-methylstyrene) equaled 56.8% with about 90% selectivity. Further gradient motion was of no practical interest due to a process selectivity decrease down to 80%. 

Conjugated Reactions of Oxidation with Hydrogen Peroxide in the Gas Phase 

The results of studies of this reaction in a hollow reactor show high selectivity up to 640 °C in the range of 4-EP volume rate from 0.065 to 0.78 h 1 and at 4-EP 20% aqueous H202 = 1 3 [94], Under optimal conditions at 620 °C, 4-VP yield equals 20.9% with 92% selectivity. Injection of quartz granules to the reactor raises the yield to 44.3% and selectivity to 96%. This is because the total surface on which, probably, the chain initiation reaction  

Concentration of active sites increases with the S/V-factor, all other parameters being equal. As a consequence, the target product yield also increases. Therefore, all following experiments were implemented in a reactor filled with quartz granules [95], A temperature increase above 640 °C abruptly reduces 4-VP yield and the process selectivity, and increases the amounts of side products (pyridine, in particular), which indicates that under definite conditions in the presence of hydrogen peroxide alkylpyridine dealkylation reaction may be implemented. 

As shown in the literature [96, 97], at low-temperatures liquid hydrogen peroxide participates in N-oxidation of pyridine bases, and the process is catalyzed by organic acids and their anhydrides. 

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