Effect of a sacrificial anode material on the electrochemical generation of phosphane oxide (H3PO)

Article abstract of DOI:10.1016/j.mencom.2014.11.005

The highest yields of phosphane oxide in the title process were obtained in electrochemical cells supplied with aluminium (49%), tin (36%) or zinc (67%) anodes.

Full text of DOI:10.1016/j.mencom.2014.11.005

Mendeleev
Communications
Mendeleev Commun., 2014, 24, 334–335
Effect of a sacrificial anode material on the electrochemical
generation of phosphane oxide (H PO)
3
Elena V. Gorbachuk,a,b Khasan R. Khayarov, Oleg G. Sinyashin and Dmitry G. Yakhvarov*
a
b
a,b
a
A. M. Butlerov Institute of Chemistry, Kazan Federal University, 420008 Kazan, Russian Federation
A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center of the Russian Academy
b
of Sciences, 420088 Kazan, Russian Federation. Fax: +7 843 273 2253; e-mail: yakhvar@iopc.ru
DOI: 10.1016/j.mencom.2014.11.005
The highest yields of phosphane oxide in the title process were obtained in electrochemical cells supplied with aluminium (49%), tin
(36%) or zinc (67%) anodes.
The phosphorous oxyacids are an important source for the produc­
tion of pharmaceuticals, fertilizers, pesticides, herbicides, flame
retardants, lubricants, etc. Thus, new methods for the selective
of active proton donors which can protonate phosphide anions
initially produced in the electrochemical process. Thus, in protic
media, all P–P bonds in white phosphorus tetrahedrons and formed
polyphosphorus intermediates are sequentially opened and phos­
1
preparation of phosphorous compounds starting from elemental
(
white) phosphorus are of high practical interest. From synthetic
phane PH is formed as the main product of the electrochemical
3
+
13
viewpoint, reagents like phosphane (PH ) and hypophosphorous
process: P + 12e + 12H
®
4PH3. From the viewpoint of
3
4
(
hypo) acid (H PO ) are of considerable importance. The phos­
electrochemical process efficiency, cathodes with high hydrogen
overvoltage, like lead and mercury, have been used.
3 2
1
4,15
phane oxide H PO is a highly reactive intermediate between a
3
reduced form of phosphorus hydride and hypo acid. According
According to the cyclic voltammetry data, the electrochemi­
to the electronic structure of H PO, the oxygen atom carries a
cally produced phosphane PH displays one irreversible peak
3
3
1
6,17
partial negative charge and phosphorus has a partial positive
of oxidation.
We were interested in the study of the products
2
charge. The high reactivity of this molecule is most likely due
formed in the oxidation process and performed the electro­
to its polarity, which converts phosphorus into an electrophile.
The charge imbalance between the P and O atoms is considerable
chemical oxidation of PH on different metal anodes in order
3
to generate phosphane oxide H PO.
3
3
to make it unstable. Note that this molecule can occur in its
Thus, we carried out the in situ generation of PH in acidic
3
4
tautomeric form as phosphinous acid H P(OH).
ethanol–water mixtures in a single electrochemical cell supplied
with sacrificial anodes of Al, Cd, Co, Mg, Ni, Nb, Sn or Zn at
2
Previously, it was considered that the phosphane oxide mole­
–
2
cule H PO does not exist at room temperature. Some experi­
a constant current density of 5 mA cm (10–20 V cell voltage).
In case of niobium and tin electrodes displaying relatively
3
mental observations of this molecule include the application of
5
18
molecular beam sampling mass spectrometry for monitoring the
high electric resistivity, the current density was limited by
–
2
reaction of atomic oxygen with PH in a discharge­flow system,
1–2 mA cm at a cell voltage increased up to 40 V.
The electrochemical reactions in the systems are shown in
Scheme 1.
3
IR spectroscopy of the photolysis products of the phosphane­
6
ozone complex in a solid state, the product of PH oxidation
3
7
by atomic oxygen in an argon matrix and the microwave spec­
8
9
trum detection of the radical H PO and the molecule H PO.
+
2
3
Cathode: P + 12H + 12e
4PH3
4
The matrix isolation and theoretical study of the photochemical
Anode: M0
Mn+ + ne
1
0
reaction of PH with OVCl and CrCl O were also described.
3
3
2
2
+
4
PH3 + 4H2O
4H3PO + 8 H + 8 e
Recently, we found that this compound can be easily generated
in solution by the mild electrochemical oxidation of phosphane
0
+
4H3PO + Mn+ + ne
Summary: P4 + 4H2O + M + 4H + 4e
11
PH generated in situ from white phosphorus (P ). Phosphane
M = Sn, Zn (n = 2), Al (n = 3)
3
4
oxide was characterized by NMR spectroscopy as free species in
solution and in a coordinated form as a ligand in water­soluble
ruthenium complexes. The phosphane oxide molecule in our
former experiments was generated in a single electrochemical
cell supplied with a sacrificial zinc anode.
Scheme 1
–
H
17.2
PO
3
–
525.2
P4
3
.5
–240.5
PH
Here, we describe the effects of sacrificial anodes made from
Al, Cd, Co, Mg, Ni, Nb, Sn and Zn on the electrochemical
reduction of white phosphorus and generation of phosphane
H
3
PO
2
3
Al
†
oxide.
Sn
The reduction of white phosphorus is irreversible and proceeds
1
2
·–
through radical anion formation: P4 + e
® P .
4
The formed P· radical anion initiates the polymerization of
–
0
–80
–160 –240
–320 –400
–480
4
d/ppm
white phosphorus leading to polyphosphorus compounds. The
derivatives containing the P–H bond are formed in the presence
Figure 1 31P NMR spectra of an acidic EtOH–H O solution of P after
2
4
electrolysis (30 min) in an undivided electrochemical cell supplied with Al
(top) and Sn (bottom) anodes.
†
For experimental details, see Online Supplementary Materials.
©
2014 Mendeleev Communications. All rights reserved.
– 334 –

Mendeleev Commun., 2014, 24, 334–335
a
Table 1 Distribution (%) of phosphorous products in the reaction mixture
not observe the coordination of phosphane oxide to anodically
generated Al , Sn and Zn cations in our experiments, we
after the electrolysis of the solution containing white phosphorus and
standard electrode potentials (E ) for the Maq /M systems, where M = Cd,
Co, Mg, Ni or Zn (n = 2) and Al or Nb (n = 3).
3+
2+
2+
0
n+
0
cannot exclude the stabilization of H PO through coordination
3
to these metals via the oxygen atom of phosphane oxide. Taking
into account the standard electrode potentials determined in
0
n+
Entry Anode
E / (M /M0)
P4
PH3
H PO
H PO2
aq
3
3
aqueous solutions, we believe that the formation of H PO is a
more complicated process than a simple function of the standard
electrode potentials of the metals used.
3
1
2
3
4
5
6
7
8
Al
–1.66
–0.40
–0.28
–2.37
–1.10
–0.25
–0.13
–0.76
17
7
traces
–
49
27
traces
–
Cd
Co
Mg
Nb
Nib
Sn
traces
traces
40
traces
traces
–
Thus, we found that the illusive phosphane oxide molecule
10
–
50
–
H PO can also be easily generated in an undivided electrochemical
3
8
–
cell supplied with sacrificial aluminium and tin anodes. These
results nicely supplement the data obtained using a sacrificial
–
–
–
–
1
1
21
2
36
32
11
zinc anode.
Zn11
7
15
67
a
b
Determined by the integral intensity of signals in the 31P NMR spectra.
This work was supported by the Russian Science Foundation
(project no. 14­13­01122).
31
The P NMR signals are not determined due to the presence of para­
2
+
magnetic Ni ions.
Online Supplementary Materials
The highest yields of phosphane oxide were obtained with Al,
Supplementary data associated with this article can be found
in the online version at doi:10.1016/j.mencom.2014.11.005.
11
Sn and Zn anodes (Table 1). The reaction mixture after 30 min
of electrolysis contained only the phosphorous products formed
in the electrochemical process (Figure 1).
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4
2
3
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3
2
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Figure 2 Cell voltage of the electroreduction of white phosphorus in acidic
ethanol–water (1:2) solution with different sacrificial anodes: Zn, Mg, Al,
Ni, Cd and Co.
Received: 9th July 2014; Com. 14/4421
–
335 –