A synergetic effect in nitrous acid formation by sonolysis of nitric acid in the presence of nitrous oxide

Article abstract of DOI:10.1023/A:1009596614257

A synergetic effect is found in the sonochemical formation of HNO₂ in HNO₃ solution in the presence of an N₂O-Ar gaseous mixture. The maximum rate of HNO₂ formation is observed at an N₂O : Ar ratio of 15 : 85 (v/v). During the sonolysis of 4 M HNO₃ solutions, the rate of HNO₂ formation increases multifold due to the synergetic effect. The rate of sonochemical hydrazine decomposition in nitrate solutions also increases considerably in the presence of N₂O.

Full text of DOI:10.1023/A:1009596614257

Russian Chemical Bulletin, International Edition, Vol. 49, No. 12, December, 2000
2077
A synergetic effect in nitrous acid formation by sonolysis of nitric acid
in the presence of nitrous oxide
S. I. Nikitenko« and A. F. Seliverstov
Institute of Physical Chemistry, Russian Academy of Sciences,
3
1 Leninsky prosp., 117915 Moscow, Russian Federation.
Fax: +7 (095) 952 5308. Å-mail: nikitenko@ipc.rssi.ru
A synergetic effect is found in the sonochemical formation of HNO2 in HNO3 solution in
the presence of an N O—Ar gaseous mixture. The maximum rate of HNO formation is
2
2
observed at an N O : Ar ratio of 15 : 85 (v/v). During the sonolysis of 4 M HNO solutions,
2
3
the rate of HNO2 formation increases multifold due to the synergetic effect. The rate of
sonochemical hydrazine decomposition in nitrate solutions also increases considerably in the
presence of N O.
2
Key words: ultrasound, nitric acid, nitrous acid, nitrous oxide, hydrazine.
wHNO /µmol L min–1
–1
It is known that the ultrasonic treatment (sonolysis)
2
of aqueous solutions of nitric acid1
—3
and nitrous oxide
4
N O produces nitrous acid, and this process consider-
80
2
ably accelerates many redox reactions. In this work, we
6
4
0
0
studied the influence of N O on HNO formation during
2
2
sonolysis of aqueous solution of HNO3.
Experimental
20
Sonolysis was carried out in a thermostatted cylindrical glass
0
50
Fig. 1. The plot of the rate of HNO2 formation vs. composition
of an N O—Ar mixture during sonolysis in water.
100 N O (vol.%)
2
reactor by an UZDN-A ultrasound dispergator (f = 21 kHz, I =
2
= 0.46 W mL–1, V = 20 mL,
2
.6 W cm–2, Ssurf = 3.5 cm , Ð
acoust
5
2
T = 20 °C) according to a previously described procedure.
An N O—Ar gas mixture with a specified composition was
2
6
prepared using the Venturi mixer. The gas mixture was bubbled
with a flow rate of 100 mL min– through the sonicated liquid
decreases the N O concentration in the gas phase corre-
1
2
sponding to the maximum rate of HNO formation.
Analysis of the rates of HNO2 formation during
sonolysis of solutions of HNO3 and NaNO3 in the
2
for 30 min before sonolysis and during sonolysis.
The concentration of HNO2 in samples taken from the
sonicated solution was determined spectrophotometrically by
the Griess method7 (ε = 42500 L cm–1 mol–1, λ = 530 nm).
The hydrazine concentration was found using the reaction with
4
-(dimethylamino)benzaldehyde7 (ε = 52600 L cm–1 mol–1
λ = 458 nm).
,
Table 1. The influence of the composition of the solution and
gas phase on the rate of sonochemical formation of HNO2 in Ar
The reaction rates were calculated from the initial portions
of the kinetic curves of HNO2 accumulation or hydrazine
decomposition. The statistical error of determination of the
reaction rate found from three parallel measurements was at
most 15%.
(wAr) and in an N2O (15%)—Ar mixture (wN O) and the value
of synergetic effect (S)
2
Solution
C
w
wAr
S
N O
2
/
mol L–1
µmol L–1 min–1
Results and Discussion
H O
HNO3
HNO3
NaNO3
NaNO3
—
1
4
1
4
78.3
79.1
360
77.4
79.5
334
—
5.4
26.7
2.5
9.2
31.0
—
0.95
3.4
0.96
0.91
3.0
2
N O bubbling in water or in solutions of HNO did
2
3
not result in the formation of HNO , and HNO was
2
2
accumulated only under the action of ultrasound. The
maximum rate of HNO2 formation is achieved at a
HNO3*
4
volume ratio of Ar : N O equal to 85 : 15 (Fig. 1),
2
* The rate of hydrazine sonolysis; the calculation of the
overall rate of HNO formation Σw = (wAr + w ) gave
whereas at an ultrasound frequency of 300 kHz this ratio
2
N O
2
4
113 µmol L–1 min
–1
is 70 : 30. Thus, a decrease in the ultrasound frequency
.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2112—2114, December, 2000.
066-5285/00/4912-2077 $25.00 © 2000 Plenum Publishing Corporation
1

2
078
Russ.Chem.Bull., Int.Ed., Vol. 49, No. 12, December, 2000
Nikitenko and Seliverstov
presence of Ar or an N O (15%)—Ar gaseous mixture
under similar experimental conditions. In the presence
2
(
Table 1) allows us to conclude the following.
a. In an Ar atmosphere the rate of HNO formation
of an N O (15%)—Ar mixture, N H sonolysis is con-
2 2 4
siderably accelerated as compared to that in pure Ar.
The value of synergetic effect for N H in 4 M HNO is
2
increases when the concentration of HNO3 or NaNO3
increases. When the concentrations of HNO and NaNO
2
4
3
close to that for HNO . Thus, the observed specific
3
3
2
are the same, the reaction rate is higher in solutions of
nitric acid.
features of the sonochemical oxidation of hydrazine are
determined by the synergetic effect of the sonochemical
formation of HNO2.
b. In the presence of N O in 4 M HNO , the overall
2
3
reaction rate (Σw) considerably exceeds the sum of the
rates of HNO2 formation during sonolysis of HNO3 in
It can be assumed that the nature of the considered
effect is related to the interaction of the sonolysis prod-
Ar (wAr) or in an N O (15%)—Ar mixture in water
ucts N O and HNO , which increase the yield of HNO .
2
2
3
2
(
wN2O). The value of synergetic effect (S) can be found
It is known2 that the sonolysis of nitric acid occurs
using the following equation:
mainly via a mechanism including the decomposition of
the HNO molecules inside the cavitation bubble and the
3
S = Σw/(wAr + w
).
(1)
NO3– ions in the liquid around the bubble. The forma-
tion of HNO2 is accompanied by the evolution of NO
N O
2
It follows from Table 1 that the synergetic effect
appears only at a sufficiently high concentration of
and NO2 into the gas phase, and the yield of NO is
2
higher than those of HNO and NO . Thus, a consider-
2
2
HNO and is absent from solutions of NaNO .
3
3
able portion of the sonolysis products of HNO3 leaves
the reaction sphere and does not participate in the
The synergetic effect also appears in the sonochemical
decomposition of hydrazine in 4 M HNO . It is known8
that the sonolysis of N H in a nitrate medium in an Ar
atmosphere is determined by the sonochemical forma-
tion of HNO2 in an HNO3 solution. The reaction rate
has the zero order with respect to hydrazine and is
approximately equal to the rate of sonochemical forma-
3
formation of HNO . Nitrous acid can also be formed via
2
2
4
the mechanism of indirect ultrasonic action, which in-
cludes the interaction of the OH• radicals with the NO3–
ions followed by the hydrolysis of the NO3• radicals
• •
H O —))) H + OH ,
(4)
(5)
(6)
(7)
2
tion of HNO , which corresponds to the following
2
•
OH + HNO3
•
NO3 + H2O,
scheme of the process:
•
NO3 + H2O
HNO3 —))) HNO2 (rate-determining step),
(2)
(3)
NO2 + H2O2,
+
HNO2 + N H
Products (fast process),
2 NO2 + H2O
HNO2 + HNO3.
2
5
where symbol "—)))" designates the sonochemical step.
The study of the kinetics of N H sonolysis in an Ar
However, the contribution of this mechanism to the
overall process is negligible. The formation rate of the
ÎH• radicals and, hence, the reaction rate (5) can be
estimated using the data on the kinetics of sonochemical
formation of H2Î2. According to the previous results,5
the rate of H2Î2 formation during water sonolysis in an
argon atmosphere, under experimental conditions
similar to our experimental conditions, amounts to
2
4
atmosphere and in an N O (15%)—Ar mixture (Fig. 2,
2
Table 1) showed that the reaction rate in the presence of
both an N O (15%)—Ar mixture and pure Ar had the
2
zero order with respect to hydrazine, and the rate of
N H sonolysis was close to the rate of HNO formation
2
4
2
3
µmol L–1 min–1, which is ∼ 10-fold lower than the rate
–
1
[
N H ]/mol L
2
4
of HNO2 formation by sonolysis of 4 M HNO3 (see
Table 1).
0
0
0
0
0
.010
.008
.006
.004
.002
It is known4 that HNO2 is not the main product of
N O sonolysis:
2
1
•
•
N O —))) N2 + O
,
(8)
(9)
2
3
••
2 O
O ,
2
•
•
O
O
+ N O
2
N2 + O2,
2 NO,
(10)
(11)
•
•
+ N O
2
2
NO
HNO2 (secondary processes
in solution).
(12)
0
20
Fig. 2. Kinetic curves of hydrazine sonolysis in 4 M HNO3:
, Ar; 2, N O (15%)—Ar; and 3, calculated curve obtained
40
60
t/min
The main portion of N O decomposes inside the
2
cavitation bubble to form N2 and O2 because the reac-
tion rates (9) and (10) exceed considerably the rates of
processes (11) and (12).
1
2
using the equation Σw = (wAr + w
).
N O
2

A synergetic effect in nitrous acid formation
Russ.Chem.Bull., Int.Ed., Vol. 49, No. 12, December, 2000 2079
The fast reaction between NO and O•• becomes
possible under the combined sonolysis of HNO3
solutions of 4 M HNO is much higher than the reaction
rate in solutions of 4 M NaNO3.
3
and N O:
2
References
•
•
NO + O
NO2.
(13)
1
2
. M. A. Margulis, Zh. Fiz. Khim., 1974, 48, 1653 [J. Phys.
Chem. USSR, 1974, 48 (Engl. Transl.)].
. L. Venault, Ph. Moisy, S. I. Nikitenko, and C. Madic,
Ultrasonics/Sonochemistry, 1997, 4, 195.
The hydrolysis of NO2 results in the formation of
HNO2 (reaction (7)). Thus, the combined sonolysis
provides an additional efficient channel of HNO2 syn-
thesis, which results in the synergetic effect. In dilute
3. S. I. Nikitenko, Ph. Moisy, and C. Madic, Radiochimica
Acta, 1999, 86, 23.
solutions of HNO3 and in solutions of NaNO , the
4. E. J. Hart and A. Henglein, J. Phys. Chem., 1986, 90, 5992.
5. S. I. Nikitenko, Izv. Akad. Nauk, Ser. Khim., 2000, 645 [Russ.
Chem. Bull., Int. Ed. Engl., 2000, 49, 649].
3
synergetic effect is not observed because the volatile
molecular form of HNO3 is virtually absent from these
solutions. Therefore, the formation of HNO2 proceeds
6
. R. H. Perry, Spravochnik inzhenera-khimika [Chemical Engi-
neers' Handbook], Khimiya, Moscow, 1969, 2, 335 (in
Russian).
only due to the decomposition of the NO – ions in the
3
solution layer surrounding the cavitation bubble:
7
8
. G. Charlot, Chimie Analytique Quantitative, Paris, 1974, 341.
. Ph. Moisy, L. Venault, S. I. Nikitenko, and C. Madic,
Sonochemical Oxidation of Hydrazinium Nitrate, U(IV) and
Pu(III) in Nitric Acid Aqueous Media, Extended Abstracts
NRC4, 2, G-P15, St. Malo, France, 8—13 September, 1996.
NO3– —))) NO2– + 0.5 O2.
(14)
In this case, NO and NO2 are virtually not formed,
and reaction (13) becomes improbable. For the same
Received June 15, 2000;
in revised form August 28, 2000
reason, the rate of sonochemical formation of HNO in
2