| Polyoxometalates (POMs) are diverse inorganic clusters, the numerous properties of which can be controlled by altering POM compositions and structures. The characteristics of POMs such as low cost, commercial availability and synthetic tractability make them very attractive for the use in various fields of chemistry and technology. The reversible redox properties of POMs as well as their thermodynamic stability to oxidation were critical for selecting POMs as an alternative to chlorine in wood pulp delignification, a major process in paper manufacturing.; The research addressed in this dissertation was a part of a team effort at Emory University and the USDA Forest Products Laboratory to develop an environmentally friendly wood pulp delignification technology, based on the use of POMs and oxygen. The goal was to investigate the kinetics and mechanism of lignin model oxidation with a representative POM.; The phenolic lignin model (3,3′,5,5 ′-tetra-tert-butylbiphenyl-4,4′ -diol) oxidation studies demonstrate that the phenolic moiety is oxidized by the POM via an outer-sphere electron transfer mechanism. The increase in the pH dramatically accelerates the reaction due to the contribution of the phenolate oxidation that becomes kinetically more significant in basic medium that is relevant to actual delignification conditions.; While studying the cation effect on the phenolic model oxidation, the ion-pairing phenomenon in POM solutions was discovered. The general relevance of ion pairing to other reactions with POMs and the lack of the quantitative studies was an impetus for a thorough investigation of this phenomenon in POM systems. For the first time, the stoichiometry of ion pairs, the ion-pair association constants and the rate of electron transfer from (alkalimetal cation - POM anion) ion pairs to a phenolic electron donor were determined. The correlations between the cation size and the rate and energy of electron transfer were established.; The kinetic studies of the non-phenolic model (anisoin) oxidation with a POM reveal that the rate-limiting step is the acid-catalyzed enolization of anisoin. As a result, neither the nature, nor the POM concentration effects the reaction rate. However, the specificity of the substrate used in this study limits the extrapolation of these conclusions to only ketol moieties in lignin. |
