New aspect of nucleophilic reactivity of tertiary phosphine oxides. R3PO-POCl3 binary system

Article abstract of DOI:10.1023/A:1013264726682

The reaction of tertiary phosphine oxides with phosphorus oxychloride was found to give triorganylphosphonium dichlorophosphates R₃PCl⁺PO₂Cl^-₂ rather than phosphorylphosphonium salts R₃P · OPOCl₂. Mixtures of the reagents, called binary system, possess a considerable synthetic potential. They are capable of converting alcohols to the corresponding alkyl chlorides.

Full text of DOI:10.1023/A:1013264726682

Russian Journal of General Chemistry, Vol. 71, No. 8, 2001, pp. 1233 1235. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 8, 2001,
pp. 1307 1309.
Original Russian Text Copyright
2001 by Kazantseva, Timokhin, Rokhin, Blazhev, Golubin, Rybakova.
New Aspect of Nucleophilic Reactivity
of Tertiary Phosphine Oxides. R PO POCl Binary System
3
3
M. V. Kazantseva, B. V. Timokhin, A. V. Rokhin,
D. G. Blazhev, A. I. Golubin, and Ya. V. Rybakova
Institute of Petrochemical and Coal Chemical Synthesis, Irkutsk State University, Irkutsk, Russia
Received April 12, 2000
Abstract The reaction of tertiary phosphine oxides with phosphorus oxychloride was found to give tri-
+
organylphosphonium dichlorophosphates R PCl PO Cl rather than phosphorylphosphonium salts R3P
3
2
2
OPOCl . Mixtures of the reagents, called binary system, possess a considerable synthetic potential. They are
2
capable of converting alcohols to the corresponding alkyl chlorides.
Nucleophilic properties of the phosphoryl oxygen
in tertiary phosphine oxides are well known. Owing phate (Me N) PCl PO Cl [4]. We consider that such
chlorohexamethyltriamidophosphonium dichlorophos-
+
2
3
2
2
to these properties, there exists a whole class of com-
plex compounds with various Lewis acids. Transition
and non-transition metal halides form stable com-
plexes with tertiary phosphine oxides, in which phos-
phorus ligands are bound with the central atom via
the phosphoryl oxygen [1]. At the same time, it is
known that some Group IV VI halides react with
a different behavior of these structurally similar com-
pounds can not be explained in terms of their structure.
The 31P NMR spectra of the reaction mixtures of a
series of triorganylphosphine oxides R P(O) (R =
3
n-Bu, benzyl, PhCH CH , Ph) with phosphorus
3
2
oxychloride contain only two singlet signals, one at
64 104 ppm and the other, at 5 to 8 ppm (see
P
P
phosphine oxides in another way. Phosphorus, arsenic, Table 1), implying lack of PP and POP coupling.
and antimony pentachlorides convert tertiary phos-
phine oxides to the corresponding halophosphoranes.
Phosgene and thionyl chloride react analogously [2].
Such ambiguity in the behavior can be explained by
the fact that with increasing electronegativity of the
Group IV VI element in the halides their reaction
products with phosphine oxides become less and less
stable, and the quasiphosphonium compound formed
in the first stage converts to triorganylphosphorane
via oxygen transfer on the ligand.
Therefore, we proposed that the obtained products are
not quasiphosphonium salts I but triorganylchloro-
+
phosphonium dichlorophosphates R PCl PO Cl II.
3
2
2
To confirm this proposal, we added to the reaction
mixtures independently prepared compounds having
common ions with the products, specifically tri-
organylchlorophosphonium hexachlorophosphorates
+
+
R PCl PCl and the Vilsmeier reagent Me N=CHCl
3
6
2
PO Cl . It occured that such additives give rise to no
2
2
3
1
new signals in the P NMR spectra. Moreover, it was
+
Cl E( O PR )
R3PO + ECl
R P O ECl
Cl
Table 1. Yields and chemical shifts in the 31P NMR
n
3 m
n
3
n
1
A
spectra ( , ppm; nitromethane) of the reaction products of
P
+
tertiary phosphines with phosphorus oxychloride
R PCl Cl + EOCln 2.
3
B
Cation in
+
Yield, R PCl PO Cl ,
%
3
2
2
+
E = Li, Zn, B, Al, Ga, Si, Sn, Sb, Bi, Ti, Zr, Cr, Mn, Ni,
Cu, U; n = 1 4; m = 1 4 (A). E = CO, SO, P, As, Sb; n =
R
R PCl PCl ,
3
6
P, ppm
P, ppm
2
, 5 (B).
Bu
PhCH2
98
82
85
82
96
102.4, 8.01a
94.3, 7.05
100.7, 3.00
65.7, 5.03
51.3, 12.6
103.2
94.1
100.7
66.5
In this connection of interest is the behavior of
tertiary phosphine oxides in reaction with phosphorus
oxychloride. As shown in [3], they form a stable
PhCH CH2
2
Ph
+
quasiphosphonium salt (R P O POCl ) Cl I. But it
(Me N)
51.3
3
2
2
is known that hexamethylphosphoric triamide
HMPA) reacts with phosphorus oxychloride to give
a
+
(
The
of Me N=C(Me)Cl PO Cl is 3.5 to 9 ppm.
P
2
2
2
1
070-3632/01/7108-1233$25.00 2001 MAIK Nauka/Interperiodica

1234
KAZANTSEVA et al.
Table 2. Yields of alkyl chlorides in the reactions of
As seen from Table 2, chlorophosphonium salt
derived from triphenyl- and tribenzylphosphine oxides
readily chlorinate primary, secondary, and unsaturated
alcohols and diols just at room temperature. The re-
action result is practically independent of the hydro-
R PClPO Cl with alcohols
3
2
2
(
Me N) PClPO Cl
2 3 2 2
Ph PCl (PhCH ) PCl
3
2 3
R
PO Cl
PO Cl
at room under carbon chain length in the alcohol. GLC data show
2
2
2
2
temperature reflux that 1 2 h after mixing of the reagents at room tem-
perature complete convertion of the alcohol to the
n-Pr
i-Pr
n-Bu
s-Bu
n-Hex
s-Hex
PhCH2
88
84
90
96
99
86
63
49
78
corresponding chloride takes place. At the same time,
the reactivity of the complex on the basis of HMPA
is considerably lower, and here 2 6-h heating is
required to convert alcohols to halides. Such a dif-
ference in the reaction rates is evidently explained by
a much more difficult substitution of the chlorine in
the chlorohexamethyltriamidophosphonium cation
compared with the chlorotriphenyl- and chlorotri-
benzylphosphonium cations, on account of the steric
and electron-donor effects of the amido group.
87
89
2.7
3.3
8.9
70
72
67
45
35
1
,4-(CH2)4
65
75
Allyl
72
37
To attest that alcohols are chlorinated by the
proposed scheme and not by reaction with phosphorus
oxychloride which can appear as a result of equilib-
rium between the complex and its components, we
performed model reactions of butanol with phos-
phorus oxychloride.
recently shown that analogous compounds are formed
by the reaction of tertiary phosphines with phosphorus
oxychloride, i.e. in the absence of structural condi-
tions for appearance of quasiphosphonium salts
+
(
R P O POCl ) Cl [5].
3
2
+
Thus, together the resulting data show that the
R PCl PO Cl
R PO + POCl .
3 3
3
3
2
reaction of triorganylphosphine oxides with phospho-
rus oxychloride, like with HMPA, gives triorganyl-
chlorophosphonium dichlorophosphates II. Such
reactions proceed rather smoothly without heating on
It was found that a day after mixing of the reagents
in xylene the yield of butyl chloride was 12%, and
after heating of the reaction mixture for 6 h it did not
mixing of the reagents in organic solvents. Increased exceed 15%. It thus can be concluded that the res-
temperature and polarity of the solvents only favor
shorter reaction times. Note that the yield of tri-
organylchlorophosphonium dichlorophosphate is close
to quantitative.
ponsibility for the chlorination of alcohols by complex
salts II is on the chlorophosphonium cation.
To facilitate the synthetic procedure, triorganyl-
phosphonium dichlorophosphates and their reaction
with alcohols leading to alkyl chlorides may be per-
formed in one pot. To this end, equimolar amounts of
phosphine oxide and phosphorus oxychloride in
organic solvent were heated with stirring for 2 h, then
alcohol is added, and the mixture is stirred again.
GLC data show that after 1 h no alcohol is present in
the reaction mixture. After hydrolysis, the starting
triorganylphosphine oxide is recovered almost quan-
titatively.
The presence in these salts of a chlorophosphonium
cation suggests facile substitution of the chlorine
under the action of various nucleophilic agents. Hence,
the reaction with alcohols should give the correspond-
ing alkyl chlorides via initial substitution of the
chlorine atom in the halophosphonium cation by
alkoxyl followed by the Arbuzov reaction. These trans-
formations may, on the one hand, provide additional
evidence for the structure of the adducts and, on the
other, demonstrate their synthetic potential.
Considering the fact that only phosphorus oxychlo-
ride is consumed in the course of the reaction, while
phosphine oxide is constantly regenerated, there is no
need in using equimolar amounts of the reagents. The
reactions of alcohols with phosphorus oxychloride in
the presence of catalytic amounts of phosphine oxide
are quite successful. GLC analysis of a mixture of
BuOH, POCl , and R PO (R = Bu, PhCH , Ph) in a
+
+
R PCl PO Cl + R OH
[R POR PO Cl ]
3
2
2
3
2
2
HCl
R PO + R Cl + HPO Cl .
3
2
2
The yields of alkyl chlorides in the reactions of
triorganylphosphonium dichlorophosphates with al-
cohols of various structure were shown to be control-
led by the phosphorus-containing reagent (Table 2).
3
3
2
1:1:0.05 molar ratio showed that after 1-h heating
the alcohol had completely converted to chloride. If
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 8 2001

NEW ASPECT OF NUCLEOPHILIC REACTIVITY
1235
this reaction is carried out at room temperature, no
more than 6 h are needed for its completion.
Chlorination of alcohols without isolation of
triorganylphosphonium dichlorophosphates. To a
solution of 2 5 g of R PO (R = Bu, benzyl, Ph) in
3
EXPERIMENTAL
20 50 ml of toluene or p-xylene, a solution of phos-
phorus oxychloride in the same solvent was added in
portions. The reaction mixture was stirred with a
magnetic stirrer and heated for 1 2 h. Then equimolar
amount of alcohol was added, and the resulting mix-
ture was stirred for an additional 1 2 h and then
subjected to GLC analysis. The yields of alkyl chlo-
rides are listed in Table 2.
All experiments were carried out in anhydrous
solvents. Alkyl chlorides were analyzed by GLC on
an LHM-8MD chromatograph (katharometer, 1500
-mm column packed with 1.5% SKTV on Chroma-
ton N, carrier gas helium, 55 60 l/min). The
3
3
1
P
NMR spectra were measured on a Varian VXR-500S
3
1
spectrometer (202 MHz). The P chemical shifts
were measured against 85% phosphoric acid.
Chlorinaton of butanol with a catalytic amount
of tributylphosphine oxide. To a mixture of 1.14 g
of tributylphosphine oxide and 12.8 g of butanol in
60 ml of anisole, 26.5 g of phosphorus oxychloride
was added dropwise. The reaction mixture was heated
under reflux with stirring 2 h and then distilled to
obtain 10.8 g (68%) of butyl chloride.
Reaction of tertiary phosphine oxides with phos-
phorus oxychloride. To a solution of R PO (R = Bu,
3
Ph, PhCH , PhCH CH ) in anhydrous solvent
2
2
2
(
benzene, toluene, hexane), a solution of equimolar
amount of phosphorus oxychloride in the same sol-
vent was added dropwise with stirring. A day later,
the precipitate that formed was filtered off and dried
REFERENCES
in a vacuum. In the case of Bu PO an oil soluble in
3
nonpolar solvents is formed. The yields of the pro-
ducts and their spectral characteristics are listed in
Table 1.
1. Lobana, T.S., The Chemistry of Organophosphorus
Compounds, Hartley, F.R., Ed., New York: Wiley,
1992, vol. 2, pp. 409 565.
2
. Metoden der organischen Chemie (Houben-Weyl),
Organische Phosphor-Verbindungen, Stuttgart: Thieme,
1982, vol. 2, p. 872.
. Binder, H. and Fluck, E., Z. Anorg. Allg. Chem., 1969,
vol. 365, pp. 170 175.
Chlorination of alcohols with chlorohexame-
thyltriamidophosphonium dichlorophosphate. To
+
a suspension of 39.8 g of (Me N) PCl PO Cl
2
3
2
2
3
in 120 ml of benzene, 10.8 g of hexanol was added.
The reaction mixture was heated under reflux with
stirring for 6 h. After hydrolysis and fractionation, 9 g
4. Domroy, J.R. and Castro, B., Tetrahedron Lett., 1997,
vol. 53, no. 20, pp. 3321 3322.
(
70%) of hexyl chloride was isolated. The other alkyl
chlorides were obtained analogously. The yields of the
products are listed in Table 2.
5. Timokhin, B.V. and Kazantseva, M.V., Zh. Obshch.
Khim., 1992, vol. 62, no. 3, pp. 706 707.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 8 2001