Russian Chemical Bulletin, International Edition, Vol. 57, No. 2, pp. 283—288, February, 2008
283
Kinetics and mechanism of the reactions of ozone
with guaiacol, veratrol, and veratrol derivatives
ꢀ
A. G. Khudoshin, A. N. Mitrofanova, and V. V. Lunin
Department of Chemistry, M. V. Lomonosov Moscow State University,
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Leninskie Gory, 119992 Moscow, Russian Federation.
Fax: +7 (495) 939 4575. Eꢀmail: khudoshin@kge.msu.ru
The kinetics of the reactions of ozone with compounds modeling structural lignin fragꢀ
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.
Key words: ozone, model lignin compounds, rate constant, mechanism, phenol, veratrol,
veratric aldehyde, veratric alcohol.
Investigation in the area of vegetable raw materials
and ligninꢀcontaining 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.
cance for the estimation of the reactivity of lignin itself in
the reactions with ozone.
The presence and nature of substituents in the aroꢀ
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
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—5
ozonolysis of these compounds is insufficient.
The 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.
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 , H O , O ,
Experimental
2
2
2
3
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and others. Ozone is one of the most efficient oxidants.
The reactions of ozone with organic compounds were studied
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To 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.
on a setup, whose scheme has been described previously. Ozone
was obtained from air using a laboratory glass ozonator in an
electric silent discharge (frequency 7 kHz, I = 40 mA, W = 4 kW).
The ozone concentrations in a gas mixture at the outlet and
inlet of the reactor were determined using a Medozon 254/3
ozonometer from the optical absorption at λ = 254 nm.
Ozonation was carried out at 298 K, at the initial ozone
–3
–1
concentration (0.9—1.1)•10 mol L , and at the volumetric
–1
flow rate of the gas mixture w = 25 L h . The volume of the
reaction mixture was 0.55 L.
3
). The dependences of the rate constants of the reactions
Ozonation was carried out as follows. A solution in the
reactor was saturated with ozone until the stationary ozone
concentration, and then the substance to be ozonated was added.
The moment, when the ozone concentrations at the inlet and
outlet of the reactor became equal, was considered as the end of
the reaction. Samples for the chromatographic analysis of the
ozonation products were taken during ozonation.
with ozone on the redox potential were determined for
compounds of the guaiacyl series, and the results obꢀ
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 signifiꢀ
The substrates were phenol (3•10 —4•10 mol L–1),
–4
–2
–4
–3
–1
2
ꢀmethoxyphenol (guaiacol) (1•10 —4•10
mol L ),
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 276—281, February, 2008.
066ꢀ5285/08/5702ꢀ0283 © 2008 Springer Science+Business Media, Inc.
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