Complexation and reactions of molecular iodine with dimethyl and diethyl sulfoxides

Article abstract of DOI:10.1134/S1070363206110235

The complexation and reactions of molecular iodine with dimethyl sulfoxide and diethyl sulfoxide in the neat sulfoxides and in their mixtrues with water were studied by conductometry, pH-metry, argentometric titration, UV spectroscopy, and GLC analysis. According to the results obtained, molecular iodine initially forms a charge-transfer complex with the sulfoxide, which subsequently undergoes chemical transformations to hydrogen iodide and the corresponding sulfones. A possible reaction mechanism was suggested.

Full text of DOI:10.1134/S1070363206110235

ISSN 1070-3632, Russian Journal of General Chemistry, 2006, Vol. 76, No. 11, pp. 1801 1803.
Original Russian Text Sh.A. Markaryan, K.R. Grigoryan, A.R. Sarkisyan, A.M. Asatryan, Ts.A. Adamyan, 2006, published in Zhurnal Obshchei Khimii,
006, Vol. 76, No. 11, pp. 1885 1887.
Pleiades Publishing, Inc., 2006.
2
Complexation and Reactions of Molecular Iodine
with Dimethyl and Diethyl Sulfoxides
Sh. A. Markaryan, K. R. Grigoryan, A. R. Sarkisyan,
A. M. Asatryan, and Ts. A. Adamyan
Yerevan State University,
ul. A. Manukyana, Yerevan, 375049 Armenia
e-mail: shmarkar@ysu.am
Received March 1, 2006
Abstract The complexation and reactions of molecular iodine with dimethyl sulfoxide and diethyl sulf-
oxide in the neat sulfoxides and in their mixtrues with water were studied by conductometry, pH-metry,
argentometric titration, UV spectroscopy, and GLC analysis. According to the results obtained, molecular
iodine initially forms a charge-transfer complex with the sulfoxide, which subsequently undergoes chemical
transformations to hydrogen iodide and the corresponding sulfones. A possible reaction mechanism was
suggested.
DOI: 10.1134/S1070363206110235
Molecular interactions in solutions containing di-
Et SO I are stronger than those of the Me SO I
2 2 2 2
alkyl sulfoxides and iodine were a subject of numer-
ous studies [1 5]. A significant contribution was
made by Klaboe [1] who, in particular, spectroscopi-
cally proved the formation of 1 : 1 charge-transfer
complexes of dimethyl sulfoxide with iodine. Previ-
ously we determined the equilibrium constants and
thermodynamic characteristics of these complexes [5].
For high concentrations of the components, formation
of iodide and triiodide ions was also considered [1 5].
It should be noted that solutions of iodine in dimethyl
sulfoxide are used in medicine [6, 7]. The biological
significance of diethyl sulfoxide also increased recent-
ly [8, 9]. It can be expected that diethyl sulfoxide
solutions can also find biomedical applications.
complexes. At the same time, the stability constant of
the Et SO I complex is higher, as shown in [5].
2
2
The UV spectra of the ternary systems Et SO
2
(
Me SO) H O iodine are characterized by two ab-
2
2
sorption maxima at about 300 and 365 nm. Figures 2a
and 2b show that the absorption intensity in both sys-
tems decreases during a period of 1 h, with this trend
being more pronounced in the Et SO-containing solu-
2
tions (Fig. 2b).
1
.6
1
2
1
1
.4
.2
3
4
5
In this study we examined the physicochemical
properties of Me SO I and Et SO I binary systems
6
1
.0
.8
0.6
2
2
2
2
and of their aqueous solutions by conductometry,
argentometric titration, and UV spectroscopy. A pos-
sible mechanism of chemical transformations of the
complexes was suggested on the basis of these data.
0
0
0
.4
.2
0
Figure 1 shows the UV spectra of solutions of I in
2
Me SO and Et SO. The absorption bands of charge-
2
2
transfer complexes formed in these systems appear in
the range 290 370 nm. It should be noted that the
band intensities in the spectra of the Me SO I sys-
300
350
400
450
500
nm
,
2
2
4
tem ([I ] 1 10 M) did not change during a period
Fig. 1. Evolution with time of the electronic absorption
2
of 1 h, whereas in the Et SO I system with the same
I2 concentration they appreciably decreased (Fig. 1).
The absorption bands of the molecular complexes
spectrum of the Et SO iodine system. Time, min: (1) 5,
2
2
2
(2) 10, (3) 25, (4) 35, (5) 45, and (6) 60 min. [I ] 1
2
4
10 M; 20 C.
1801

1802
MARKARYAN et al.
(
a)
(b)
2
1
.0
.8
2.0
1.8
1.6
1.4
1.2
1
1
2
2
3
3
1
1
.6
.4
4
4
5
5
6
6
1
1
.2
.0
1.0
0.8
0.6
0.4
0.2
0
0
0
.8
.6
.4
0
.2
0
0
3
00 350 400 450
500 550
nm
300 350 400 450
500 550
, nm
,
Fig. 2. Evolution with time of the electronic absorption spectra of the systems (a) Me SO H O iodine and (b) Et SO H O
2
2
2
2
iodine. Time, min: (1) 5, (2) 10, (3) 25, (4) 35, (5) 45, and (6) 60. Composition of the mixed solvent Me SO (or Et SO) : H O =
2
2
2
4
4
: 1 (volume ratio), [I ] 1 10 M, 20 C.
2
However, in the Me SO I H O system, in con-
ratios) were determined at a constant I concentration
of 1.25 10 M and were compared with the data for
the sulfoxide/water binary systems. It should be noted
2
2
2
2
2
trast to the anhydrous system, the gradual decrease in
the absorption is also appreciable, and this trend be-
comes more pronounced with an increase in the water
content and temperature. Figure 3 shows the kinetic
that the conductivity of Et SO is considerably higher
2
than that of Me SO [10], and the same appeared to be
2
dependences of the optical density of I solutions in
true for the aqueous solutions: The conductivity of the
2
Me SO H O at three different temperatures.
Me SO water system varied in the range from 5 to
2
2
2
1
6
S m depending on the water content, whereas for
The gradual chemical transformations of the molec-
ular complexes sulfoxide iodine also follow from the
conductometric and pH-metric data. The electrical
conductivities of the binary systems Me SO I and
Et SO water system at the same temperature it was
2
2 3 times higher. The Et SO-based system showed
2
also higher conductivity in the presence of iodine.
Whereas in the system Me SO H O I the conductiv-
2
2
2
2
2
Et SO I , and also of the corresponding ternary sys-
ity increased by a factor of less than 10, in the system
Et SO H O I it increased by a factor of more than
2
2
tems with water (at different sulfoxide/water volume
2
2
2
2
0 (see table). The table also shows that pH of the
system tends to decrease in the presence of I , which
2
1
.8
.6
.4
is due to the formation of HI. The formation of the I
anion was confirmed by argentometric titration. It is
interesting that the I concentration in the system with
1
1
1
Et SO is two times higher compared to the system
2
1
1
.2
.0
with Me SO. Another important feature of the system
2
with Et SO is the formation of the triiodide ion: I +
2
I = I .
2
2
0
.8
.6
.4
.2
2
Gas-chromatographic measurements revealed the
0
presence of sulfones (R SO ) in these systems.
2
2
Based on the data obtained, we suggest the following
pathway of chemical transformations of the complexes
R SO I :
0
3
0
2
2
0
500
1000
1500
2000
Time, s
R SO + I + H O
R SO + 2HI,
2 2
2
2
2
R = CH , C H .
3
2 5
Fig. 3. Kinetic curves of the Me SO water iodine
2
system at (1) 20, (2) 40, and (3) 60 C. Volume ratio
However, as noted above, an excessive amount of
HI is formed in the system with Et SO, in contrast to
4
Me SO : H O = 2 : 1,
295 nm, [I ] 1 10 M.
2
2
max
2
2
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 11 2006

COMPLEXATION AND REACTIONS OF MOLECULAR IODINE
1803
Conductivity and pH of the systems Me SO (Et SO) H O and Me SO (Et SO) H O I at 20 Ca
2
2
2
2
2
2
2
Solvent
volume ratio)
Solvent
(volume ratio)
10 , Sm 1
4
pH
10 , Sm
4
1
pH
(
Me SO
10.415
7.890
7.447
7.605
3.632
3.522
3.456
3.322
5.93
6.25
6.38
6.42
9.42
10.13
11.56
12.12
Me SO I2
3.664
3.625
3.598
3.574
1.502
1.475
1.385
1.348
40.0
41.5
47.3
51.8
207
220
265
281
2
2
7
5
4
Me SO 1H O
7Me SO 1H O I
2
2
2
2
2
2
2
Me SO 1H O
5Me SO 1H O I
2
2
2 2
Me SO 1H O
4Me SO 1H O I
2 2
2
2
Et SO
Et SO I2
2
2
7
5
4
Et SO 1H O
7Et SO 1H O I
2
2
2
2
2
2
2
Et SO 1H O
5Et SO 1H O I
2
2
2
2
Et SO 1H O
4Et SO 1H O I
2
2
2
2
a
The conductivities of straight Me SO and Et SO coincide with those reported in [10].
2
2
that with Me SO. Therefore, an additional pathway of
HI formation is suggested for solutions of iodine in
diethyl sulfoxide:
ezon on Chromosorb. The column temperature was
145 C, and the temperature of the thermal conductiv-
2
ity detector, 175 C. The carrier gas was He, flow rate
1
2
0 ml min . Iodide ion was determined by argento-
(
C H ) SO + I
CH =CH S(O) CH CH + 2HI.
metric titration.
2
5 2
2
2
2
3
A similar reaction (dehydrogenation of the electron
REFERENCES
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3
4
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2
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6
7
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RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 76 No. 11 2006