Thermal disproportionation of hypophosphorous acid

Article abstract of DOI:10.1023/B:RJAC.0000008318.22178.07

Thermal disproportionation of hypophosphorous acid was studied to find the reaction order, the rate constant and activation energy of the process, and also the temperature ranges in which the reaction rate is the highest.

Full text of DOI:10.1023/B:RJAC.0000008318.22178.07

Russian Journal of Applied Chemistry, Vol. 76, No. 8, 2003, pp. 1354 1355. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 8, 2003,
pp. 1392 1393.
Original Russian Text Copyright
2003 by Shechkov, Pevneva, Meshkova.
BRIEF
COMMUNICATIONS
Thermal Disproportionation of Hypophosphorous Acid
G. T. Shechkov, I. A. Pevneva, and O. A. Meshkova
Polzunov Altai State Technical University, Barnaul, Russia
Received April 18, 2003
Abstract Thermal disproportionation of hypophosphorous acid was studied to find the reaction order,
the rate constant and activation energy of the process, and also the temperature ranges in which the reaction
rate is the highest.
The use of red phosphorus is based on its capabil-
ity to be oxidized (manufacture of matches, getters,
fire-retardants, and components of pyrotechnic for-
mulations) [1 3]. The oxidation yields phosphorous
acids (hypophosphorous H PO , phosphorous H PO ,
measuring the gas volume was 5%. A solution of
calcium chloride served as a locking liquid.
Analysis for PH was carried out on an LKhM-80
3
chromatograph by the technique described in [6].
Gas samples (1 ml) were taken from the reactor at
intervals of 10 15 min through a hermetic tap made
of special rubber. Polysorb-1 served as absorbent.
3
2
3
3
and phosphoric H PO ) and phosphine PH . The for-
3
4
3
mation of these products may result both in retrogra-
dation of properties of phosphorous composites and in
shortening of guaranteed shelf lives of articles based
on red phosphorus.
1
The flow rate of the carrier gas was 24 ml min ; col-
umn temperature, 60 C; measurement error, 3%.
Phosphine for constructing a calibration plot was ob-
tained by hydrolysis of aluminum phosphide and an-
alyzed both chemically and chromatographically.
However, the kinetics and temperature ranges of
transformation of phosphorus acids have not been
analyzed in studies devoted to phosphorus oxidation
A thermal analysis of H PO was carried out with
00-mg samples on an MOM Q-1500D (Hungary)
[
2 4]. The main goal of the present study was to an-
3
2
2
alyze the fundamental aspects of phosphine formation
in disproportionation of hypophosphorous acid of var-
ied concentration and to determine the temperature
ranges and kinetic parameters of the process
derivatograph in standard ceramic crucibles at a heat-
1
ing rate of 10 deg min .
We revealed low- (30 90 C) and high-temperature
(
110 200 C) regions of phosphine evolution in dis-
3
H PO
2H PO + PH3.
(1)
3
2
3
3
proportionation of H PO . At low temperatures, the
3
2
acid reacts with water to give hydrogen, which was
detected by mass-spectrometry:
We studied 50% hypophosphorous acid of reagent
grade, TU (Technical Specification) 6-09-1462 76.
The acid was diluted with twice-distilled water and
concentrated by recrystallization, as described in [5].
H PO + H O
H PO + H2.
(2)
3
2
2
3
3
The disproportionation was monitored by evolution
At high temperatures (>110 C) the disproportiona-
tion process (1) occurs at the highest rate at 130
of PH in the temperature range (30 160) 1.5 C in
3
a glass reactor connected to an AGB-67M automated
gas burette.
160 C, being complete at 190 C. The process is com-
plicated by gas-phase oxidation of phosphine, begin-
ing at 120 C and ending in combustion of the gas
mixture above 160 C.
The acid (5 g) was placed in a glass dish mounted
on a quartz hook fastened to a ground tap wrench by
a fiberglass thread. A sample was rapidly (10 s) intro-
duced into the reactor with a furnace, using the tap
wrench.
Kinetic curves of disproportionation are S-shaped.
The rate of H PO disproportionation grows with
3
2
the concentration of the acid increasing from 30 to
90%, the disproportionation being of the autocatalyt-
ic nature. This feature seems to be associated with
The sensitivity of the installation was 0.001 to
ml, depending on a burette volume. The error in
1
1
070-4272/03/7608-1354 $25.00 2003 MAIK Nauka/Interperiodica

THERMAL DISPROPORTIONATION OF HYPOPHOSPHOROUS ACID
1355
the dependence of the rate of tautomeric regrouping
of H PO from the inactive form, containing phospho-
rus(V), to the active form, containing phosphorus(III).
According to the derivatographic data, the activa-
tion energy of H PO disproportionation in the range
3
2
3
2
1
110 140 C is 69.8 2 kJ mol , in satisfactory agree-
ment with the activation energy obtained from the ki-
The rate constant of the regrouping is extremely low,
k = 10 12
s
1
[4]. Raising the concentration, temper-
1
netic data (85 2 kJ mol ).
ature, and time presumably removes diffusion hind-
rances for this regrouping.
The forming H PO disproportionates in the range
90 270 C, with simultaneous oxidation of the evolv-
3
3
1
ing PH . According to the derivatographic data, the
At 110 and 140 C and process duration of 40
60 min the evolution of phosphine occurs in the ki-
netic mode and further passes to the diffusion mode.
With the temperature increasing to above 140 C,
the process passes to the diffusion mode within 40
3
maximum rate of PH oxidation is observed in the
1
3
range 280 300 C. The corresponding activation en-
1
ergy is 207 10 kJ mol .
RERERENCES
1
20 min. The disproportionation reaction in the kinet-
ic mode at high temperatures (110 170 C) is first-
5
1
1. Van Wazer, I.R., Phosphorus and Its Compounds,
order with rate constant k = 1.96 10 s and activa-
New York: Interscience, 1958, vol.1.
1
tion energy of 85 2 kJ mol . The transition of
2
3
. Speranskaya, G.V., Talanov, N.D., and Aziev, L.G.,
Zh. Prikl. Khim., 1978, vol. 54, no. 8, p. 1705.
. Korolev, V.V., Talanov, N.D., and Astakhova, G.V.,
Izv. Akad. Nauk SSSR, Neorg. Mater., 1986, vol. 22,
no. 7, pp. 1214 1216.
the reaction of phosphine evolution from the kinetic to
diffusion mode results from the accumulation of the
more thermally stable products H PO and H PO ,
3
3
3
4
which are formed upon PH oxidation:
3
4
5
6
. Brodskii, A.A., Blankshtein, V.A., Ershov, V.A., and
Talanov, N.D., Pererabotka fosfora (Processing of
Phosphorus), Leningrad: Khimiya, 1985.
. Karyakin, Yu.V. and Angelov, N.N., Chistye khimi-
cheskie veshchestva (Pure Chemical Substances),
Moscow: Khimiya, 1974.
. Potemkin, L.V. and Musatova, Yu.G., Gazokhromato-
graficheskie metody opredeleniya sostava gazovykh
vybrosov v fosfornoi promyshlennosti: Uchebnoe pos-
obie dlya rabochikh professii (Gas-Chromatographic
Methods for Determining Composition of Gas Dis-
charges in Phosphorus Industry: Tutorial for Operators),
Moscow: NIITEKhKhIM, 1985.
4
PH3 + 5O2
2P O + 6H2,
(3)
(4)
2
5
P2O5 + 3H O
2H PO .
2
3
4
A pronounced endothermic effect is observed in
the derivatograms at 135 C. It is determined by the
equilibrium the endothermic processes of dehydration
and disproportionation of H PO and also by the exo-
3
2
thermic oxidation of the evolving phosphine. The
overall activation energy of dehydration, hydration,
and disproportionation of H PO below 100 C is
3
2
1
4
4
1 kJ mol .
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 76 No. 8 2003