Selective oxidation of saturated hydrocarbons at secondary positions

The selectivity in the oxidation of saturated hydrocarbons by oxygen in pyridine-acetic acid in presence of an iron catalyst and zinc is strongly dependant on the oxygenation of the reaction mixture; using air and slow stirring, it is possible to attack adamantane and $\text{trans}$-1,4-dimethylcyclohexane almost exclusively at the secondary positions.