Oxidation of 1,2- and 1,4-Dihydroxybenzene by Birnessite in Acidic Aqueous Suspension

Abstract

Abstract--The rate and extent of oxidation of dihydroxybenzenes (DHB) to quinones in acetate-buffered suspensions of synthetic hirnessite were studied using Mn dissolution to monitor reaction progress. Concentration of free in 2+ in the aqueous phase was continuously monitored by electron spin resonance, and ultraviolet-visible (UV-VIS) spectroscopy was utilized to quantify dihydroxybenzene and quinone concentrations. Although dissolution of the oxide and release of Mn 2 + to solution generally accompanied phenol oxidation, a threshold oxidation level had to be exceeded before Mn 2+ appeared in solution. Once this threshold was surpassed, the mole quantity of Mn 2+ dissolved equaled the mole quantity of organic oxidized for 1,4-DHB, but exceeded the quantity of organic oxidized for 1,2-DHB. Thus, the latter phenol was more efficient in dissolving the oxide. Soluble phosphate suppressed Mn 2 § release without influencing the degree of organic oxidation, suggesting that phosphate chemically interacted with reduced Mn to hinder its dissolution. UV spectra provided tentative evidence for the transitory existence of Mn 3 +-1,4-DHB complexes in the solution phase.Infrared spectra of the birnessite after reaction with 1,4-DHB indicated some new features, which may have been a result of the reduction of surface Mn atoms to the 3 + oxidation state. These features were not present after reaction with 1,2-DHB, confirming that the latter phenol efficiently dissolved the oxide to release Mn 2+. Although the initial Mn dissolution was very rapid and was attributed to a surface reaction, further slow Mn release accompanied by more complete oxidation of the phenols suggests a process limited by the rate of dissolution of the solid.

Effect of organic reducing agents on the p sorption product formed on noncrystalline hydrous fe oxide

“…Changes in the IR spectra of P sorbed on Fe gel took place when the amount of hydroquinone was 960/.tmol or higher, which is more than 30 times the lower limit for ascorbic acid. A similar difference in the reactivity among position isomers of polyphenols was also observed in the oxidative reaction of the polyphenols in the presence of hydrous Fe oxide and Mn oxides (Shindo and Huang 1984;McBride 1989).…”

Reaction kinetics and transformation products of 1-naphthol by Mn oxide-mediated oxidative-coupling reaction

“…According to the reaction model of oxidative coupling, it was assumed that the reaction was initiated by the surface complexation of the hydroxyl group of a reactant to the manganese atom on the oxide surface [26,27], which is affected by the pK a of the reactant, the surface charge of Mn oxide and the solution pH [28]. The effect of the solution pH was examined by carrying out a series of batch experiments at different solution pHs ranging from 2 to 11.…”

Oxidation of Phenol in Acidic Aqueous Suspensions of Manganese Oxides

“…Manganese oxides can act as electron-transfer agents in reactions that involve phenolic compounds and molecular oxygen (Ono et al, 1977;Stone and Morgan, 1984;McBride, 1987McBride, , 1989aMcBride, , 1989bStone, 1987;Kung and McBride, 1988;Ulrich and Stone, 1989). The manganese +2, +3, and +4 oxidation states appear to be involved in electron-transfer reactions, but the factors influencing the reactions are still poorly understood.…”