1070-4272/03/7608-1214 $25.00 C 2003 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 76, No. 8, 2003, pp. 1214!1220. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 8, 2003,
Original Russian Text Copyright C 2003 by Kazakov, Rubtsov, Lempert, Manelis.
OF SYSTEMS AND PROCESSES
Kinetics of Oxidation of Organic Acids by Ammonium Nitrate
A. I. Kazakov, Yu. I. Rubtsov, D. B. Lempert, and G. B. Manelis
Institute for Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, Russia
Received January 10, 2003
Abstract-Kinetics of oxidation of some organic acids by ammonium nitrate was studied. Temperature
dependences of the rate constants of acid oxidation were determined.
Gas-generating formulations for household pur-
poses have been intensively developed in recent years.
Systems of this kind can be created using the prin-
ciples on which design of solid mixture fuels is based.
The fuel system proposed must have an acceptable
thermal stability and retain its working properties dur-
ing a rather prolonged test at elevated temperatures.
A possible way to solve this problem is to use mix-
tures of ammonium nitrate (AN) with organic sub-
stances and, in particular, oxalic acid.
It has been established previously that thermal
decomposition of AN into ammonia and nitric acid
proceeds via its equilibrium dissociation. The rate
of the process in decomposition of a pure salt is de-
termined by the rate of oxidation of the NH
a molecule of nitric acid : the rate grows with in-
creasing content of nitric acid in the system. The con-
tent of HNO
in molten pure AN does not exceed
0.1% of the total content of NO
ions in the salt, and,
therefore, the stability of pure AN is sufficiently high
for this compound to be used in the mixtures under
consideration. Introduction of organic acids into AN
can raise the equilibrium concentration of HNO
correspondingly, impair the stability of AN. However,
organic acids in aqueous solutions are much weaker
than nitric acid, with the difference in pK values be-
tween nitric and organic acids constituting 3 units and
more . Therefore, it would be expected that the in-
crease in the concentration of HNO
will be small,
and the thermal stability of the mixture, sufficient.
The aim of the present study was to analyze the ki-
netics and mechanism of the reaction of oxidation of
various organic, mainly dibasic acids by ammonium
nitrate in order to elucidate the general pattern and
distinctions of this reaction for different acids and to
assess the possibility of practical use of mixtures of
The kinetic pattern of heat release in thermal inter-
action of AN mixtures with oxalic, malonic, succinic,
pimelic, malic, tartaric, citric, maleic, and benzoic
acids in a 1 : 1 molar ratio was studied. Also, separate
experiments were carried out for mixtures of AN with
decane and polyethylene for comparison purposes.
The 1 : 1 ratio of the amounts of oxalic acid and AN
corresponds to equivalent of the oxidizing agent and
the fuel. For all other mixtures there exists an excess
of the fuel, but the equal number of moles allows
easier comparison of the positions of acid3base equi-
libria. For a mixture of AN with succinic acid, addi-
tional experiments were carried out at the stoichio-
metric ratio of the components for the oxidation reac-
tion. Chemical reagents of chemically pure and ana-
lytically pure grades were used.
The experiments were performed on a DAK-1-1
automated dynamic microcalorimeter  in sealed
glass ampules having no cool parts, which allows
preservation of all the products in the reaction zone.
If not specified otherwise, a two-component mix-
ture of the compositions mentioned above exists in
the form of a homogeneous liquid phase at any of
the temperatures studied. The rate of the reaction be-
tween the solid phases is below the detection limit of
the calorimeter. The mixture of AN with oxalic acid
shows a sufficiently high reaction rate even at 70oC,
and that with malonic acid, at 85oC; for other acids
the rate becomes comparable only above 100oC, when
the liquid phase appears in the system.
Figure 1 shows as an example kinetic curves of
heat release for the mixture of AN with oxalic acid;
for malonic, succinic, pimelic, tartaric, and benzoic
acids the curves are mainly similar and differ only in
the heat release rate and the range of temperatures