1070-4272/03/7608-1354 $25.00 C 2003 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 76, No. 8, 2003, pp. 1354!1355. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 8, 2003,
Original Russian Text Copyright + 2003 by Shechkov, Pevneva, Meshkova.
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) . The oxidation yields phosphorous
acids (hypophosphorous H
, phosphorous H
and phosphoric H
) and phosphine PH
. The for-
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.
However, the kinetics and temperature ranges of
transformation of phosphorus acids have not been
analyzed in studies devoted to phosphorus oxidation
. The main goal of the present study was to an-
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
We studied 50% hypophosphorous acid of reagent
grade, TU (Technical Specification) 6-09-1462376.
The acid was diluted with twice-distilled water and
concentrated by recrystallization, as described in .
The disproportionation was monitored by evolution
in the temperature range (303160) + 1.5oCin
a glass reactor connected to an AGB-67M automated
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
The sensitivity of the installation was 0.001 to
1 ml, depending on a burette volume. The error in
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
chromatograph by the technique described in .
Gas samples (1 ml) were taken from the reactor at
intervals of 10315 min through a hermetic tap made
of special rubber. Polysorb-1 served as absorbent.
The flow rate of the carrier gas was 24 ml min
umn temperature, 60oC; measurement error, +3%.
Phosphine for constructing a calibration plot was ob-
tained by hydrolysis of aluminum phosphide and an-
alyzed both chemically and chromatographically.
A thermal analysis of H
was carried out with
200-mg samples on an MOM Q-1500D (Hungary)
derivatograph in standard ceramic crucibles at a heat-
ing rate of 10 deg min
We revealed low- (30390oC) and high-temperature
(1103200oC) regions of phosphine evolution in dis-
proportionation of H
. At low temperatures, the
acid reacts with water to give hydrogen, which was
detected by mass-spectrometry:
O 6 H
At high temperatures (>110oC) the disproportiona-
tion process (1) occurs at the highest rate at 1303
160oC, being complete at 190oC. The process is com-
plicated by gas-phase oxidation of phosphine, begin-
ing at 120oC and ending in combustion of the gas
mixture above 160oC.
Kinetic curves of disproportionation are S-shaped.
The rate of H
disproportionation grows with
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