Abstract
The kinetics of the reaction between 1,2,3-trihydroxybenzene (pyrogallol) and O2 (autoxidation) have been determined by monitoring the concentration of dissolved dioxygen with a polarographic oxygen electrode. The reaction is carried out in pseudo-first-order excess pyrogallol, 25°C, 0.08 M NaCl, and 0.04 M phosphate buffer in the pH range 6.9–10.5. Data collection precedes reaction initiation, but only the data recorded after the estimated 3.2 s dead time are used in kinetics calculations. Observed rate constants are corrected for incomplete mixing, which is treated as a first-order process that has an experimentally determined mixing rate constant of 4.0 s−1. The rate law for the reaction is −d[O2]/dt=kapp[PYR]tot[O2], in which [PYR]tot is the total stoichiometric pyrogallol concentration. A mechanism is presented which explains the increase in rate with increasing [OH−] by postulating that H2PYR− (k2) has greater reactivity with dissolved dioxygen than does H3PYR (k1). The data best fit the equation kapp=(k1 + k2KH[OH−])/(1 + KH[OH−]) when the value of the hydrolysis constant KH (the quotient of the pyrogallol acid dissociation and water autoprotolysis constants) for this medium equals 3.1×104 M−1. The resulting values of k1 and k2, respectively, equal (0.13 + 0.01) M−1 s−1 and (3.5 plusmn; 0.1) M−1 s−1. This reaction is recommended as a test reaction for calibrating the dynamic response of an O2-electrode. © 1993 John Wiley & Sons, Inc.