Chromium stearate and chromium acetylacetonate are very active catalysts both for the oxidation of hydrocarbons by molecular oxygen and for the decomposition of organic hydroperoxides. During these reactions they also catalyze the oxidation of secondary alcohols to the corresponding ketones by organic hydroperoxides. From organic hydroperoxides and chromium(III)compounds chromium (VI) compounds are formed which are probably the effective agents oxidizing secondary alcohols to ketones.
The relative rates of autoxidation at 140°C in the presence of 0.1% manganeous sterate were determined for 9 normal alkanes, 5 secondary alcohols, and 6 ketones. In the case of the n‐alkanes the oxidation rates increase linearly with the increasing chain length of the hydrocarbon. The oxidation rates of the secondary alcohols are about 3.3 times higher than those of the corresponding alkanes. The oxidation rates of the ketones are about 1.2 times higher than those of the corresponding alkanes.
The catalytic decomposition of cumene, 1‐methylcyclohexyl and cyclohexyl hydroperoxides was studied in cyclohexane, cis‐ and trans‐1,4‐dimethylcyclohexane and cis‐pinane as the solvents. The stearates and the acetylacetonates of manganese, cobalt and chromium, the acetylacetonates of molybdenum and vanadium, n‐butyl orthoborate and n‐butyl metaborate were used as the catalysts. The chromium‐, vanadium‐, molybdenum‐ and boron‐containing catalysts brought about some Hock‐type decomposition of cumene hydroperoxide and thus proved to be acidic. Of these more of less acidic catalysts only molybdenyl acetylacetonate effected a partially stereospecific hydroxylation of the tertiary CH‐bonds in cis‐ and trans‐1,4‐dimethylcyclohexane. The well‐known selectivity of chromium catalysts for the ketone formation during the decomposition of secondary hydroperoxides is caused by the catalytic oxidatio of secondary alcohols by hydroperoxides in the presence of chromium compounds.
In the presence of all the catalysts used the free‐radical pathways of the hydroperoxide decomposition predominated, and the attack of the intermediate radicals on the starting hydroperoxide was more important than the attack on the solvent molecules.
By computer simulation of the dependencies of the mole numbers of the ketones and alcohols derived from the starting paraffin, of the acids and esters, and in some cases also of the lower alkan‐2‐ones on the paraffin conversion relative rate constants were determined on the basis of a plausible kinetic model of the paraffin oxidation. The data obtained show that about 67% of the oxidation proceeds via bifunctional primary products. With the aid of the relative rate constants determined a good simulation of the experimental mole number‐conversion curves is possible.
The mole numbers of the starting paraffins, of the intermediate alcohols and ketones with the same chain lengths, of the lower alkan‐2‐ones, of the carboxylic acids, and of the esters were determined at different reaction times for the oxidations of n‐tridecane, n‐tetradecane, and n‐pentadecane with molecular oxygen at 140°C in the presence of 0.1% Mn‐stearate. In the stationary region of the oxidation about 1.2 moles of acids and 0.7 moles of esters are formed from 1 mole of paraffin consumed. The relative oxidation rates of alcohols and of ketones with reference to the starting paraffins were estimated from the mole numbers of the starting paraffins, the alcohols and the ketones at the maxima of the alcohols and the ketones. These values are higher than those determined by competitive oxidations, and this discrepancy is an indirect evidence of the formation of bifunctional intermediates from the starting paraffins. The relative rates of the formation of alcohols, ketones, and bifunctional products from normal paraffins were estimated.
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