Clock reactions are rare kinetic
phenomena, so far limited mostly
to systems with ionic oxoacids and oxoanions in water. We report a
new clock reaction in cyclohexanol that forms molybdenum blue from
a noncharged, yellow molybdenum complex as precursor, in the presence
of hydrogen peroxide. Interestingly, the concomitant color change
is reversible, enabling multiple clock cycles to be executed consecutively.
The kinetics of the clock reaction were experimentally characterized,
and by adding insights from quantum chemical calculations, a plausible
reaction mechanism was postulated. Key elementary reaction steps comprise
sigmatropic rearrangements with five-membered or bicyclo[3.1.0] transition
states. Importantly, numerical kinetic modeling demonstrated the mechanism’s
ability to reproduce the experimental findings. It also revealed that
clock behavior is intimately connected to the sudden exhaustion of
hydrogen peroxide. Due to the stoichiometric coproduction of ketone,
the reaction bears potential for application in alcohol oxidation
catalysis