Kinetic studies on oxidation of veratryl alcohol by laccase-mediator system. Part 2. The kinetics of dioxygen uptake

The kinetics of dioxygen uptake in the laccase-catalyzed oxidation of verat ryl alcohol with dioxygen in the presence of ABTS, the mediator, was studie d. The kinetics of dioxygen uptake consists of two phases: (1) the initial phase up to a reaction time of one hour, and (2) the second phase, after a reaction time of one hour. In the initial phase, ABTS is mainly oxidized to the corresponding cation radical. The kinetics of dioxygen uptake follows a pseudo-zero order rate law. The dioxygen uptake under the reaction condit ion correlates with the initial ABTS concentration according to the stoichi ometric relationship of 0.25 moles dioxygen per mole ABTS. In the second ph ase, veratryl alcohol is mainly oxidized to veratraldehyde. The kinetics of the dioxygen uptake follows a pseudo-first order rate law. The dioxygen up take correlates linearly with the yield of veratraldehyde. The stoichiometr ic ratio between the formation of veratraldehyde and the consumption of dio xygen differs slightly at different M/S ratios. On average, however, it is 0.42 moles of dioxygen per one mole of veratraldehyde formed. The reaction mechanism is discussed on the basis of the kinetic data.