Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 1, pp. 67−70.
Pleiades Publishing, Ltd., 2012.
Original Russian Text © Yu.V. Polenov, E.V. Egorova, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 1, pp. 70−74.
AND INDUSTRIAL ORGANIC CHEMISTRY
On a Kinetic Model of Vat Dye Reduction
by Sodium Alkanesulﬁ nates
Yu. V. Polenov and E. V. Egorova
State Chemical Engineering University, Ivanovo, Russia
Received April 15, 2011
Abstract—Kinetic data obtained in the reaction of vat dye reduction with sodium alkanesulﬁ nates with and without
diffusion hindrance are compared. A common stage-by-stage mechanism of the process is suggested.
As regards their importance for coloration of textile
materials, vat dyes occupy a leading position in dyeing
and printing of fabrics produced from cellulose ﬁ bers
and their mixtures with synthetic ﬁ bers. The annual
world’s consumption of vat dyes is 120 000 tons .
A characteristic structural feature of vat dye
molecules is the presence of no less than two ketone
groups in the chromophore system with conjugated
double bonds. Under the action of reducing agents in
an alkaline medium, ketone groups are transformed to
enolic groups to give soluble leuco compounds . The
role of reducing agents is commonly played by sodium
dithionite (industrial term hydrosulﬁ te) in dyeing
processes and by sodium hydroxymethanesulﬁ nate
(HMS; industrial product rongalite C) in printing.
Previously, results of an experimental study of the
process of vat dye reduction by sodium hydroxy- and
anminoalkanesulﬁ nates with and without mass-transfer
stages have been reported [3–5].
It is of interest to compare kinetic data obtained in
various experimental conditions in order to develop
a generalized kinetic model of the process of vat dye
reduction by the reducing agents mentioned above.
The reaction of vat dye reduction in an aqueous-
alkaline solution with mass-transfer stages was
performed in a photometer cuvette of special design
under agitation at a rate of 100 rpm, which provided
a suspended state of the dye suspension. A solution of
a reducing agent was introduced into the cuvette. To
preclude oxidation of a leuco form, an inert gas, argon,
was bubbled through the reaction mixture. In the course
of the reaction, the optical density was measured at an
effective wavelength of 580 nm, which corresponds
to the maximum absorption for the oxidized form and
minimum absorption for the reduced form of the dye
under the Bouger–Lambert–Beer law. The concentration
of the leuco form of the dye in the solution volume
was calculated from the measured values of the optical
density of the solution and numerical values of the molar
absorption coefﬁ cients of the oxidized and reduced
forms of the dye.
The reduction reaction in the absence of mass-transfer
stages was performed with vat dyes in the form of
a planar nonporous disk having an open side and placed
in an aqueous-alkaline solution of the reducing agent,
through which argon was bubbled. The disk was rotated
at a rate of 800 rpm, which provided that the reaction
occurred under kinetic control. In the course of the
reaction, the reaction mixture was sampled to determine
the leuco form concentration by the spectrophotometric
method. The experimental procedure was described in
more detail in [3, 5].
The amount of the reduced form of the dye in the
surface layer of the solid phase was calculated for the
case of mass-transfer stages by using Nernst’s model of