The kinetics of the reactions of ozone with compounds modeling structural lignin frag ments, viz., phenol, guaiacol, veratrol, veratric aldehyde, and veratric alcohol, was studied. The reaction rate constants were calculated using the mass transfer model for the chemical reaction based on the film theory. The rate constants of the reactions of ozone with compounds of the veratryl series were calculated by the Hammett equation. The major ozonation products of the studied compounds were determined by HPLC. The ozonation mechanism was proposed.Investigation in the area of vegetable raw materials and lignin containing materials processing is a priority direction of the modern science. The main methods for the conversion of lignocellulose materials are related to delignification for the preparation of cellulose during paper production and its fermentation to sugars followed by the synthesis of alcohols; in addition, lignin serves as a potential raw materials for obtaining various useful products.Lignin is an irregular polyfunctional polymer built of the phenylpropane structural units. One of the specific features of lignins is their ability to oxidation, and various structures and groups of a lignin macromolecule are of different activity. The oxidants are often O 2 , H 2 O 2 , O 3 , and others. Ozone is one of the most efficient oxidants. 1To understand the mechanism of lignin oxidation by ozone, it is convenient to use compounds modeling various fragments of natural lignins, namely, guaiacol, veratrol, syringol, and their derivatives.Literature publications concern mainly qualitative data on the influence of the nature and position of substituents in the aromatic ring of the model lignin compounds on their ability to react with ozone (for guaiacol and veratrol, see Ref. 2; for coniferyl alcohol and ferulic acid, see Ref.3). The dependences of the rate constants of the reactions with ozone on the redox potential were determined for compounds of the guaiacyl series, and the results ob tained were found to be well described by the Hammett equation with the reaction constant ρ = -3.1.Quantitative data on the influence of the substrate structure on the reactivity toward ozone for model lignin compounds are few, although they are of principal signifi cance for the estimation of the reactivity of lignin itself in the reactions with ozone.The presence and nature of substituents in the aro matic ring can affect the reactivity and mechanism of the reactions of ozone with the model lignin compounds. The number of published works devoted to the mechanism of ozonolysis of these compounds is insufficient.
2-5The purpose of the present work is to establish the mechanism and a quantitative relationship between the structure of compounds of the veratryl series and their reactivity in the reactions with ozone.
ExperimentalThe reactions of ozone with organic compounds were studied on a setup, whose scheme has been described previously. 6 Ozone was obtained from air using a laboratory glass ozonator in an electric silent discharge (fre...
The reaction of ozone with lignin in aqueous acidic solutions is investigated. The Danckwerst model is used to describe the kinetics of gas/liquid processes occurring in a bubble reactor. The efficient ozo nation rate of a soluble lignin analog, sodium lignosulfate, is determined. The main lines of the reaction between ozone and lignin are revealed on the basis of kinetic analysis results and IR and UV spectroscopy data.
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