Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 11, pp. 1667−1675.
Pleiades Publishing, Ltd., 2012.
Original Russian Text © R.E. Khoma, A.A. Shestaka, V.O. Gel’mbol’dt, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 11, pp. 1656−1665.
AND INDUSTRIAL ORGANIC CHEMISTRY
On Interaction of Sulfur(IV) Oxide with Aqueous
Solutions of Ethanolamines
R. E. Khoma
, A. A. Shestaka
, and V. O. Gel’mbol’dt
Physico-Chemical Institute of Environmental and Human Protection, Odessa, Ukraine
Mechnikov National University, Odessa, Ukraine
Odessa National Medical University, Odessa, Ukraine
Received July 3, 2011
Abstract—Potentio- and conductometric titration was used to study the interaction in sulfur(IV) oxide–
ethanolamines–water systems in comparison with the previously obtained pH-metric data on how the corresponding
onium sulﬁ tes, hydrosulﬁ tes, and pyrosulﬁ tes are formed. The ionic and molecular compositions of these solutions
were calculated. Correlations between the characteristics of pH-metric titration curves of aqueous solutions of
ethanolamines with sulfur(IV) oxide and the relative stability of onium sulfates were revealed.
This study proceeds with the systematic effort aimed
to develop the theoretical foundations for catching of
acid gases with organic bases . It has been shown
that ethanolamines (Am) and aqueous solutions of
ethanolamines and their carboxylates are promising
According to pH-metric titration data, the interaction
in sulfur(IV) oxide–ethanolamines–water systems is
accompanied by the formation of the corresponding
onium sulﬁ tes (at a SO
: Am component ratio 1 : 2),
hydrosulﬁ tes, and pyrosulﬁ tes (SO
: Am = 9 : 10) [6,
7]. The fact that the second peak in the differential
pH-metric curves obtained in titration of aqueous
solutions of Am with gaseous sulfur(IV) oxide does
not correspond to the expected equimolar ratio (1 : 1)
is due to the hydrosulﬁ te–pyrosulﬁ te equilibrium [6, 7].
A qualitative characterization of this equilibrium can
be provided by redox potentiometry . A successful
experience of joint use of conductometry and redox
potentiometry for determining the composition of the
compounds being formed is known .
It should be noted that only data on the relative
stability of ethanolammonium sulﬁ tes in aqueous
solutions were reported in . There is no information
about the ionic-molecular composition of sulfur(IV)
A topical task in this context is to reveal existence
regions of various sulfur-containing molecular and ionic
forms in aqueous solutions, the nature of equilibria
between these forms, and relative stabilities of the
complexes being formed.
To study these aspects of the process of sulfur(IV)
oxide chemisorption by aqueous solutions of organic
bases, we examined the interaction of SO
solutions of ethanolamines by independent methods of
potentio- and conductometry and subjected previously
obtained experimental data  to mathematical
processing in order to determine the ionic-molecular
composition of absorbing systems and to reveal
correlations between characteristics of pH-metric
titration curves and the relative stability of the complex
salts being formed.
As starting substances served reagents of for-syn-