Cu-catalyzed oxidative phosphorylation of alkanols with white phosphorus and H2O2

Article abstract of DOI:10.1080/10426500214291

Oxidative phosphorylation of alkanols with white phosphorus in the presence of catalytic amounts of CuCl₂ has been effected. The reaction proceeds in the aqueous H₂O₂-HCl system exothermically to form dialkylphosphites and trialkylphosphates in a total yield of up to 35%. Conditions for selective synthesis of dialkylphosphites in moderate yield have been found.

Full text of DOI:10.1080/10426500214291

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Phosphorus, Sulfur, and Silicon and the Related
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Cu-Catalyzed Oxidative Phosphorylation of Alkanols
with White Phosphorus and H 2 O 2
a
b
a
b
Boris Trofimov , Boris Timokhin , Nina Gusarova , Marina Kazantseva & Alexander
b
Golubin
a
A. E. Favorsky Irkutsk Institute of Chemistry , Russian Academy of Sciences , Siberian
Branch, Irkutsk, Russia
b
Department of Chemistry , Irkutsk State University , Irkutsk, Russia
Published online: 27 Oct 2010.
To cite this article: Boris Trofimov , Boris Timokhin , Nina Gusarova , Marina Kazantseva & Alexander Golubin (2002) Cu-
Catalyzed Oxidative Phosphorylation of Alkanols with White Phosphorus and H 2 O 2, Phosphorus, Sulfur, and Silicon and the
Related Elements, 177:10, 2385-2390, DOI: 10.1080/10426500214291
To link to this article: http://dx.doi.org/10.1080/10426500214291
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Phosphorus, Sulfur and Silicon, 2002, Vol. 177:2385–2390
Copyright �C 2002 Taylor & Francis
1
042-6507/02 $12.00 + .00
DOI: 10.1080/10426500290110469
Cu-CATALYZED OXIDATIVE PHOSPHORYLATION OF
ALKANOLS WITH WHITE PHOSPHORUS AND H O
2
2
a
b
a
Boris Trofimov, Boris Timokhin, Nina Gusarova,
b
b
Marina Kazantseva, and Alexander Golubin
A. E. Favorsky Irkutsk Institute of Chemistry of the Russian
Academy of Sciences, Siberian Branch, Irkutsk, Russiaa
and Department of Chemistry, Irkutsk State University,
Irkutsk, Russiab
(
Received March 19, 2002)
Oxidative phosphorylation of alkanols with white phosphorus in the
presence of catalytic amounts of CuCl has been effected. The reaction
2
proceeds in the aqueous H O HCl system exothermically to form di-
2
2
alkylphosphites and trialkylphosphates in a total yield of up to 35%.
Conditions for selective synthesis of dialkylphosphites in moderate yield
have been found.
Keywords: Alkanols; catalytic system CuCl
2
2 2
H O ; dialkylphosphites;
phosphorylation; trialkylphosphates; white phosphorus
INTRODUCTION
The traditional synthetic methods for the preparation of esters of three-
and four-coordinate phosphorus acids are based on the reactions of
1
phosphorus chlorides with oxygen-centered nucleophiles. However, de-
spite the simplicity and efficiency, this way has significant disadvan-
tages. Preparation of the initial phosphorus chlorides involves handling
of elemental chlorine, which is not only highly toxic, but also causes no-
ticeable wearing of the equipment. On this background, the use of white
phosphorus looks as an attractive alternative for the preparation of
phosphorus acids, employing the so called “chlorine-free technologies.”
The formation of trialkylphosphites upon phosphorylation of alka-
nol solutions (MeOH or EtOH) of alkali metal alcoholates with white
phosphorus was reported in a dissertation by G. Kahl.2 The reaction
Address correspondence to Boris Trofimov, A. E. Favorsky Irkutsk Institute of
Chemistry of the Russian Academy of Sciences, Siberian Branch, Favorsky Street 1,
6
64033, Irkutsk, Russia. E-mail: bat@irioch.irk.ru
2
385

2
386
B. Trofimov et al.
is accompanied by the evolution of an equimolar amount of PH3.
Introduction of carbon tetrachloride in this system inhibits the for-
3
,4
mation of PH3.
The interaction of white phosphorus with CCl4
and alcohols in polar aprotic solvents also results in formation of
5
,6
trialkylphosphites.
In Dorfman et al.,
7
� 9
reaction of white phosphorus with alcohols in
the presence of a 20-fold molar excess (in relation to phosphorus) of
copper(II) salts was reported to afford the esters of three- and four-
coordinate phosphorus acids in a high yield, although no experimental
details were given. The necessity of using substantial amounts of copper
salts renders this method almost useless in the preparative aspect.
The aim of the present investigation is the search for new approaches
to the synthesis of three- and four-coordinate phosphorus acid esters,
starting from white phosphorus and alkanols.
White phosphorus is known to be readily oxidized by salts of metals
1
0
possessing low redox potentials. Additionally, the possibility of three-
coordinate phosphorus atom halogenation with copper(II) chloride, was
shown earlier.11
Thus, one may assume that in the system P4 CuCl2 ROH at the
initial reaction step, the reduction of divalent copper ion to Cu(I) would
occur, with simultaneous formation of phosphorus chloride which, in
turn, can react in situ with alkanol.
Therefore, one should expect that introduction of a reagent capable of
oxidizing Cu(I) to Cu(II) to the reaction mixture would secure the below
catalytic cycle of the alkanols phosphorylation with white phosphorus
(
Scheme 1).
SCHEME 1
RESULTS AND DISCUSSION
In order to check the above assumption, we have studied the phospho-
rylation of alkanols with white phosphorus in the presence of catalytic

Phosphorylation of Alkanols
2387
amounts (5–20 mas% of phosphorus mass) of copper(II) chloride and a
cooxidant.
Ethanol and n-butanol exothermically react with white phosphorus
in the system CuCl2 H2O2 HCl H2O to produce dialkylphosphites
1
a,b and trialkylphosphates 2a,b at complete phosphorus conversion
(
Scheme 2, Table I).
SCHEME 2
The aggregate state of white phosphorus was found to affect the
result of the reaction studied. The use of fine-dispersed phosphorus or
the so-called “phosphorus snow” prepared by rapid cooling of intensively
stirred emulsions of white phosphorus in benzene—n-butanol mixture
(
1:1 volume ratio) is more efficient for the synthesis of products 1b,2b,
TABLE I Phosphorylation of Alkanols with White Phosphorus in the
CuCl
Run
2
H
2
O
2
HCl H
CuCl2,
O Systema
2
Product yield, %b
(RO)2P(O)H (RO)3P O
HCl,c
mol per 1 P atom
mol per 1 P atom
1
2
3
4
5
6
0.045
0.090
0.023
0.045
0.045
0.045
2.00
4.00
1.00
Not used
0.09
2.00
14
11
21
15
15
18
25
10
24
11
24
2
Not found
7
12
2
25
5
d
7
8
9
0.250
4.00
d
aEthanol (run 1) or n-butanol (runs 2–9) were used in the reaction. In all runs,
the volume ratio alkanol:benzene was 1:1; the molar ratio P:H2O2 (30% aqueous
�
solution was used) was 1:2 and the reaction temperature was in the range 15–22 C.
b
The yields of dialkylphosphite and trialkylphosphate were determined based
on their relative content in the reaction mixture calculated from the ratio of
integral intensities of the peaks in the 31P NMR spectrum; in all runs the phos-
phorus conversion was 100%.
c
A concentrated aqueous solution of HCl was used.
Copper(II) chloride and HCl were not added to the reaction mixture. Instead,
d
aqueous phases obtained in runs 3 and 5, respectively, were used.

2
388
B. Trofimov et al.
rather than using solutions of phosphorus in benzene or suspension of
phosphorus in n-butanol.
Under best conditions, the total yield of ethyl esters 1a,2a is 25%
(
Table I, run 1) and that of n-butyl esters 1b,2b is 35% (Table I, run 2).
3
1
According to the P NMR data, along with the above mentioned
products, the reaction mixture contains also mono- and dialkylphos-
phates.
The use of hydrogen peroxide complexes with urea or with sodium
carbonate, as well as ammonium persulfate as oxidants in this reaction
results in lowering (by � 2–3 times) of the yield of the products 1b,2b.
It is known that oxidation of Cu(I) to Cu(II) can be performed by
passing oxygen into hydrochloric aqueous solutions of copper(I) chloride
�
12
�
at a temperature of � 95 C. However, on heating (85–95 C) n-butanol
with white phosphorus and the system CuCl2 HCl H2O with oxygen
flow, the products 1b and 2b are practically not formed.
The efficiency and chemoselectivity of n-butanol phosphorylation
in the system CuCl2 H2O2 HCl H2O significantly depend on the
amount of copper salt used (Table I). Thus, increasing the content of
the latter results in a higher yield of trialkylphosphate 2b (Table I,
compare runs 3 and 8).
The aqueous phase formed under the above conditions can be used
instead of CuCl2 for repeated phosphorylation of n-butanol with white
phosphorus. The reaction is thus directed toward predominant forma-
tion of dibutylphosphite 1b (Table I, runs 7 and 9). When the reaction
is carried out with 20-fold molar excess of copper(II) chloride relative
to P4 in the absence of hydrogen peroxide, such as under the conditions
9
10
used in Dorfman et al. and Van Wazer, only phosphate 2b in 60%
yield is formed.
In the example with n-butanol, it was shown that the reaction can be
carried out in the absence of HCl. Moreover, it leads to a drastic increase
of the process chemoselectivity: Exclusive formation of dibutylphos-
phite 1b in a yield of up to 15% is observed (Table I, run 4).
Copper(II) sulfate and acetate can be employed in this reaction to
give similar results.
EXPERIMENTAL
31P NMR spectra were taken on the following spectrometers: Varian
VXR-500S (202 MHz operating frequency) and Bruker DPX 400 (400
3
1
and 162 MHz). The P chemical shifts were measured relative to 85%
phosphoric acid.

Phosphorylation of Alkanols
2389
Phosphorylation of ethanol (Table I, run 1). To a suspension of 2.5 g
(
20.1 mmol) of white phosphorus in 100 ml of benzene-ethanol mix-
�
ture (1:1 volume ratio), prepared by rapid cooling to 0–5 C of the hot
�
(
(
50–60 C) emulsion, a solution of 0.5 g (3.7 mmol) of CuCl2 in 14.8 ml
168.9 mmol) of concentrated hydrochloric acid was added. To the ob-
tained mixture, 16.5 ml (160.1 mmol) of 30% aqueous H2O2 was added
dropwise during 1 h upon cooling with ice and stirring. A self-heating
�
of the reaction mixture to 20–22 C was observed and the mixture color
turned from brown to light green. The mixture was stirred for an ad-
ditional 0.5 h at rt. The aqueous layer thus formed was separated and
the organic layer was twice washed with water. After that, water and
unreacted ethanol were removed from the combined aqueous solutions
using a rotary evaporator, the residue was distilled in vacuum and a
�
fraction with b.p.5.0 of 70–80 C was collected. A total of 2.6 g of a mixture
of diethylphosphite and triethylphosphate was obtained. According to
the 31P NMR data, the mixture contained 14% of diethylphosphite (�P
1
0.4 ppm, JP� H 690 Hz) and 11% of triethylphosphate (�P 2.1 ppm).
Phosphorylation of n-butanol (Table I, run 2). To a suspension of 2 g
(
16.1 mmol) of white phosphorus in 100 ml of benzene-n-butanol mix-
�
ture (1:1 volume ratio), prepared by rapid cooling to 0–5 C of the hot
�
(
(
50–60 C) emulsion, a solution of 0.4 g (3.0 mmol) of CuCl2 in 11.8 ml
134.6 mmol) of concentrated hydrochloric acid was added. To the ob-
tained mixture, 13.2 ml (128.1 mmol) of 30% aqueous H2O2 was added
dropwise during 1 h upon cooling with ice and stirring. A self-heating
�
of the reaction mixture to 20–22 C was observed and the mixture color
turned from brown to light green. The mixture was stirred for an ad-
ditional 0.5 h at rt. The aqueous layer thus formed was separated
and the organic layer was twice washed with water. After removal of
the volatile components from the organic phase using a rotary evap-
orator the residue was distilled in vacuum and a fraction with b.p.1.0
�
1
10–130 C was collected. A total of 4 g of a mixture of dibutylphosphite
31
and tributylphosphate was thus obtained. According to the P NMR
data, the mixture contained 18% of dibutylphosphite (�P 10.7 ppm, JP� H
6
83 Hz) and 12% of tributylphosphate (�P 2.3 ppm).
Dibutylphosphite (IIa) (Table I, run 4). To a cooled to 5–10 C mixture
�
of 28.6 g (386.5 mmol) of n-BuOH and 0.6 g (4.4 mmol) of copper(II)
chloride in 30 ml of benzene, a solution of 3 g (24.2 mmol) of white
phosphorus in 120 ml of benzene, and 21.7 g (191.5 mmol) of 30% aque-
ous solution of hydrogen peroxide, preliminarily neutralized with bar-
ium hydroxide to pH = 7, were simultaneously added dropwise using
two dropping funnels during 1.5 h. A self-heating of the reaction mix-
�
ture to 30–35 C was observed and the mixture color turned from dark

2
390
B. Trofimov et al.
brown to light blue. Two layers thus formed were separated. The upper
organic layer was evaporated and the residue was distilled in vacuum
�
31
to give 2.8 g (15%) of dibutylphosphite, b.p.1.0 75–77 C. P NMR spec-
trum: �P 7.68 ppm (a doublet, JP� H 680 Hz).
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[
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[
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