Mechanism of decomposition of sodium hydroxymethanesulfinate in aqueous solution

Article abstract of DOI:10.1023/A:1012384629829

Sodium hydroxymethanesulfinate decomposes in air in three stages. The first stage involves oxygen, the second is the induction period, and the third occurs without oxygen. Reactions occurring in these stages are suggested. Additions of surfactants hinder

Full text of DOI:10.1023/A:1012384629829

Russian Journal of General Chemistry, Vol. 71, No. 5, 2001, pp. 675 678. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 5, 2001,
pp. 722 725.
Original Russian Text Copyright
2001 by Polenov, Egorova, Pushkina.
Mechanism of Decomposition of Sodium
Hydroxymethanesulfinate in Aqueous Solution
Yu. V. Polenov, E. V. Egorova, and V. A. Pushkina
Ivanovo State University of Chemical Engineering, Ivanovo, Russia
Received July 9, 1999
Abstract Sodium hydroxymethanesulfinate decomposes in air in three stages. The first stage involves
oxygen, the second is the induction period, and the third occurs without oxygen. Reactions occurring in these
stages are suggested. Additions of surfactants hinder diffusion of oxygen through the surface film formed on
the solution air phase boundary and thus inhibit the first stage of the process.
Sodium hydroxymethanesulfinate (rongalite) is a
commercially produced reductant. It is used in diverse
fields, such as printing and dyeing of textiles, synthet-
ic rubber production, synthesis of stabilizers for poly-
meric materials, etc. [1]. One of the problems arising
when using rongalite is its poor stability. Decompo-
sition reactions occurring concurrently with the target
reactions result in overexpenditure of rongalite in
industrial processes. Fore example, in the rongalite
potash procedure for fabric printing, rongalite is added
to the dyeing formulation in a sixfold amount relative
to that required for reduction of the vat dye [2].
rongalite and the zero order with respect to oxygen
were found in [5]. The rate constants obtained from
the experiments with no additives coincide within
experimental error with those reported in [5]. The rate
constants K were calculated by the zero-order ki-
2
netic equation for the sections of the kinetic curves
corresponding to gradual decrease of the rongalite
concentration with time (correlation factor r =
0.97 0.998). The degree of rongalite decomposition
was determined before the onset of the final stage.
Data in the table (decrease in the degree of ronga-
lite decomposition before induction period in an inert
gas atmosphere and in the decomposition rate in the
initial period in the presence of surfactants) suggest
that in the initial stage rongalite decomposes by oxi-
dation with atmospheric oxygen. Insignificant decom-
position of rongalite in an inert atmosphere is due to
Decomposition of rongalite was studied in numer-
ous works [3, 4]. However, experimental data were
mainly obtained for the inert atmosphere, and these
data are apparently insufficient for quantitative de-
scription of the process. This study was aimed at
elucidating in more detail the reaction mechanism and
obtaining kinetic data on rongalite decomposition in
air, i.e., under conditions of rongalite use in practice.
Figure 1 shows the kinetic curves of decomposition
of sodium hydroxymethanesulfinate in aqueous solu-
tion in air (in the absence and in the presence of sur-
factants) and under an inert gas. Three characteristic
sections (process stages) can be distinguished in the
kinetic curves. In the first, initial stage the reaction
is relatively fast, and from 5 to 15% of the initial
amount of rongalite is consumed. The second stage is
the induction period in which the reductant concentra-
tion remains practically constant. In the third stage,
the rongalite concentration gradually decreases.
Fig. 1. Variation with time of the sodium hydroxymethane-
The kinetic parameters of the reaction under vari-
sulfinate concentration C
: (1) without adding sur-
HMS
ous conditions are listed in the table. K is the rate
1
factants, (2) with addition of Fenoksol, (3) with addition of
Meteks, and (4) under argon without adding surfactants;
the same for Figs. 2 5.
constant in the initial stage, calculated by the first-
order kinetic equation. The first order with respect to
1
070-3632/01/7105-0675$25.00 2001 MAIK Nauka/Interperiodica

676
POLENOV et al.
Kinetic parameters of decomposition of sodium hydroxymethanesulfinate in aqueous solution at 343 K
3
3
3
K2 103,
Reaction
conditions
K1 10 ,
K2 10 ,
Reaction
conditions
K1 10 ,
,
%a
, %a
min 1
mol l min 1
1
min 1
mol l 1 min
1
In air, no additions
Under inert gas,
no additions
6.8 0.5
7.0 0.5
1.2 0.6
0.8 0.2
11
3
Meteks added
Fenoksol added
1.3 0.6
0.9 0.4
0.8 0.1
0.8 0.3
14
11
a
(
) Degree of decomposition in the initial section of the kinetic curve.
a minor amount of oxygen dissolved in water or intro-
duced with rongalite powder. This conclusion agrees
with the results obtained by Koksharov et al. [6] who
found that the limiting stage of oxidative decomposi-
tion of rongalite is phase transfer of oxygen; the reac-
tion occurs in a 7.3 8.5- m surface layer.
HOCH SO2
HSO2 + CH O,
(1)
(2)
(3)
(4)
(5)
2
2
.
2
HSO2 + 2O2
.
2O + SO2 + H+,
2O + 2H+
O2 + H O ,
2
2 2
2
SO + 2OH
SO + H O,
3 2
2
Inhibition of rongalite decomposition in the pres-
ence of added surfactants may be due to formation on
the solution surface of a film consisting of surfactant
molecules, decelerating (by a factor of 1.65 according
to [6]) the oxygen uptake by the surface.
2
2
SO + H O2
SO + H O.
4 2
3
2
These reactions proceed at a noticeable rate until
the amount of the accumulated CH O becomes suffi-
2
Oxidative decomposition of rongalite can be de-
scribed by the following scheme [5]:
cient to shift the equilibrium of reaction (1) to the left
and attain the quasiequilibrium. The inhibiting effect
of formaldehyde was observed in [1, 4].
The major decomposition products in the ini-
tial period, according to reactions (1) (5), are
2
3
2
4
CH O, SO , and SO . However, the kinetic curves
2
(
Figs. 2, 3) show that, firstly, sulfite is not the final
reaction product: Its concentration reaches a max-
imum in the first stage and then starts to decrease.
Secondly, decrease in the sulfite concentration is ac-
companied by accumulation of dithionite which can
form by reversible reaction (6) [7]:
HSO3 + HSO2
S2O 24 + H O.
(6)
2
2
Fig. 2. Variation of the SO concentration with time.
Simultaneously with this reaction, formaldehyde
in the induction period disproportionates by the Can-
nizzaro reaction:
3
2
CH O + H O
HCOOH + CH OH.
(7)
2
2
3
This is suggested by a decrease in the solution pH
Fig. 4). The induction period ends when the solution
(
pH decreases to 4 5, and in acidic solution dithionite
starts to rapidly decompose (Fig. 3).
According to published data [7], decomposition of
dithionite involves noncatalytic reaction (8) yielding
active (noncolloidal) sulfur and autocatalytic reac-
tion (9):
2
Fig. 3. Variation of the S O concentration with time.
2
4
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 5 2001

MECHANISM OF DECOMPOSITION OF SODIUM HYDROXYMETHANESULFINATE
677
2
H S O
Sa + 3SO2 + 2H O,
(8)
(9)
2
2
4
2
3
H S O
H S + 5SO + 2H O.
2
2
4
2
2
2
The latter reaction is catalyzed by H S, SO , and
2
2
active polymeric sulfur species. Formation of H S and
2
active sulfur species (S ) was detected by us previous-
a
ly in polarographic studies of deaerated acidic solu-
tions of rongalite [4].
Despite formation in reactions (8) and (9) of sulfite
sulfur (SO ), its concentration does not increase in the
2
final stage (Fig. 2). This is due to a reversible reaction
2
3
of sulfite (SO , HSO , SO ) with formaldehyde; in
2
3
acidic solutions the equilibrium is shifted toward for-
mation of the formaldehyde bisulfite adduct.
Fig. 4. Variation of the pH of the reaction medium with
time.
HSO3 + CH O
HOCH SO .
(10)
2
2
3
Acidification of the solution due to reaction (7) is
accompanied by decomposition of the dithionite [reac-
tions (8) and (9)], binding of formaldehyde by reac-
tion (10), and shift of the equilibria of reactions (6)
and (7) to the right, which causes decomposition of
rongalite in the final stage of the process (Fig. 1).
Thiosulfate is apparently the final product of ron-
galite decomposition, as suggested by the shape of the
kinetic curves (Fig. 5). It is formed by the reaction be-
tween the decomposition products, sulfite and active
sulfur:
xHSO3 + Sa
HS O .
(11)
2
3
2
Fig. 5. Variation of the S O concentration with time.
2
3
All the reactions occurring in the final period of
decomposition take place both in the presence and in
the absence of atmospheric oxygen.
The main substance content, determined by iodomet-
ric titration [8], was no less than 99.4%. As support-
ing electrolytes for polarographic studies we used the
Robinson Britton universal buffer mixture prepared
from H BO , CH COOH, H PO , and NaOH (chemi-
Additions of surfactants decrease the rate of oxida-
tive decomposition but have practically no effect on
the degree of decomposition (see table). Therefore,
their use with the aim to reduce the loss of the reduc-
tant is appropriate in fast processes occurring in a thin
layer of the solution, e.g., in finishing of textiles.
When reduction with rongalite occurs in the bulk of
solution, the use of such additives is not appropriate.
3
3
3
3
4
cally pure grade). To construct the calibration curves
polarographic weight height vs. concentration), we
used chemically pure grade Na S O 5H O, Na SO ,
(
2
2
3
2
2
3
and Na S O . The concentrations of their solutions
2
2
4
were determined by iodometric titration [8]. As sur-
factants we used Fenoksol BV-9/10 and Meteks
Our results suggest a complex mechanism of ron-
galite decomposition in the presence of atmospheric
oxygen, involving both oxidative decomposition in
the surface layer and reactions occurring in the bulk
of solution without participation of oxygen.
(
Khimprom Joint-Stock Company, Ivanovo).
The kinetics of sodium hydroxymethanesulfinate
decomposition was studied at 343 0.5 K. Rongalite
solutions (0.60 0.65 M) were prepared in distilled
water preheated to the required temperature. In the
course of decomposition of the aqueous solution, pH
was monitored with an EV-74 pH meter, and solution
samples were taken at regular intervals and analyzed
for sodium hydroxymethanesulfinate (iodometric titra-
EXPERIMENTAL
In our study we used sodium hydroxymethanesul-
finate (rongalite) HOCH SO Na 2H O prepared by
2
2
2
2
2
2
double recrystallization of the technical-grade product.
tion) and the S O , SO , and S O ions (polaro-
2 4 3 2 3
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 5 2001

678
POLENOV et al.
graphically). In some experiments, a surfactant was
added in an amount of 0.5 wt % relative to rongalite.
The solutions were not stirred, except the experiments
in an inert atmosphere in which a continuous flow of
argon was passed through the solution before heating
and in the course of decomposition.
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PU-1 polarograph in a two-electrode glass electro-
chemical cell. A mercury dropping electrode (drop-
ping period 4 s) was the working electrode, and the
bottom mercury, the reference electrode. To prevent
oxidation of the compounds with atmospheric oxygen,
the supporting electrolytes were purged in the cell
with argon. To determine the content of dithionite, the
polarograms were taken in the classical polarographic
mode in the supporting electrolyte (pH 9) from the
1
971.
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1
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no. 7, pp. 1161 1164.
0
.9 V; the rate of potential sweeping was 4 mV s .
To determine the content of thiosulfate and sulfite
present simultaneously, the polarograms were taken in
supporting electrolytes of pH 4.7 in the differential
mode, with a sweeping amplitude of +11 mV, from
the initial potential of +0.3 V to the final potential
of 1 V.
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