Hydrogenolysis of alkyl‐substituted adamantanes, diamantanes, and triamantanes in the gas phase on a nickel‐alumina catalyst

Dealkylation of several alkyladamantanes, diamantanes, and triamantanes has been observed in the gas phase with hydrogen at atmospheric pressure on a 30% nickel‐alumina catalyst. Yield‐temperature profiles show that the optimum temperature for obtaining the pure parent compound in high yield can be as low as 215 °C. The ease of removal of an alkyl substituent depends on whether it is secondary or tertiary on the diamondoid nucleus. Rupture of the diamondoid skeleton requires much higher temperatures (over 280 °C) than dealkylation. The hydrogenolytic degradation of diamantane to adamantane was examined with the aid of molecular mechanics calculations; likely pathways for CC bond cleavage were deduced which are consistent with the several intermediates detected experimentally. The mechanism of dealkylation is discussed in terms of steric and thermodynamic factors and the nature of possible surface intermediates.