1070-4272/03/7608-1356 $25.00 C 2003 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 76, No. 8, 2003, pp. 1356!1357. Translated from Zhurnal Prikladnoi Khimii, Vol. 76, No. 8, 2003,
Original Russian Text Copyright + 2003 by Kisil’, Osadchenko, Tomilov.
Stability of Phosphorus Trihalide Solutions Used in Polarography
L. M. Kisil’, I. M. Osadchenko, and A. P. Tomilov
State Research Institute of Organic Chemistry and Technology, Moscow, Russia
Received January 15, 2003
Abstract-The behavior of PCl
solutions in acetonitrile containing no more than 0.02 wt % H
storage at room temperature was studied.
Previously [1, 2] we have studied the polarograph-
ic behavior of phosphorus trihalide solutions. It was
shown that their stability depends on the water con-
tent in the solvents.
In this study, we analyze the stability of phosphorus
trihalide solutions in acetonitrile, used in polarography.
Since phosphorus trihalides are readily hydrolyzed
by water and react with protic organic solvents, their
polarographic behavior is studied in aprotic solvents
As shown previously, polarograms of phosphorus
trihalides at 20325oC in dimethylformamide and ace-
tonitrile dried by the procedure described in  show
well defined waves.
The stability of phosphorus trihalides in acetonitrile
solutions with composition similar to that used in
polarographic studies  (no more than 0.02% H
was monitored by UV spectroscopy. The absorption
spectra of straight acetonitrile and acetonitrile solu-
tions of PCl
, and HCl (HCl is the main hydro-
lysis product of PCl
in water) are shown in the fig-
ure. The PCl
spectrum contains two bands peaked at
298 and 365 nm. The PI
spectrum contains three
bands at 250, 293, and 370 nm. As seen from the fig-
ure, no appreciable amount of HCl is formed in the
solution, i.e., PCl
is not hydrolyzed in aceto-
nitrile solution during the experiment.
The UV spectrum of acetonitrile solution of PCl
did not change during its storage for a week. This in-
dicates that PCl
is not hydrolyzed noticeably in ace-
tonitrile containing up to 0.02% water, i.e., acetoni-
trile purified by the procedure described in  is suit-
able as a solvent for polarography. This is confirmed
by the fact that the polarogram of PCl
containing no more than 0.02% water does not change
after storage of this solution at +3 to +5oC for 7 days.
After longer storage, especially at room temperature,
the limiting current decreases and a wave appears at
more negative potentials. For example, the limiting
current of reduction of a 0.23 M PCl
ing 0.08 M tetraethylammonium perchlorate as a sup-
porting electrolyte decreases from 1.298 to 1.200 mA
in 12 days.
When the water content is higher than 0.02%,
the half-wave potential of PCl
reduction is shifted
to the cathodic region:
Water content, % 0.02 0.03 0.06 0.10
, V 0.915 0.930 0.960 1.920
At water content of 0.06%, a second wave appears
= 31.93 V (relative to bottom Hg ). This is due
to reaction of PCl
O present in the solvent.
UV spectra of (1) straight acetonitrile and acetonitrile so-
lutions of (2) HCl, (3)PCl
, and (4)PI
density and (l) wavelength.