Note: Descriptions are shown in the official language in which they were submitted.
CA 02255161 1998-12-03
The present invention relates to the preparation of
mono- and di-arylphosphines.
BACKGROUND OF THE INVENTION
There are known processes to prepare arylphosphines
by reacting, for example, phosphorus trichloride with a
Grignard reagent or with an organolithium compound, followed
by hydrolysis, extraction and distillation. These processes
have disadvantages, in that materials used in the processes
are expensive, corrosive, difficult to prepare owing
particularly to their sensitivity to moisture, and cumbersome
to handle on a large scale.
SUMMARY OF THE INVENTION
In one aspect the present invention provides a
process for preparing a mono- or d1- arylphosphine, which
process comprises reacting an aryl compound bearing a leaving
group attached to a carbon atom of the aromatic ring with
phosphine in the presence of a Group VIII metal catalyst.
In accordance with the invention it is possible to
avoid or alleviate many of the abovementioned disadvantages by
reacting phosphine with an aryl compound in the presence of,
preferably, a palladium catalyst.
A particular advantage of the present invention is
that it is possible to obtain mono-arylphosphines and di-
arylphosphines, 1.e., primary and secondary arylphosphines, in
good yield, and accompanied by only relatively small amounts
of triaryl, 1.e., tertiary phosphine. Owing to the high
reactivity of phosphorus compounds, reactions to form
arylphosphines usually proceed quickly to the triaryl
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compound. Consequently, triarylphosphines are available much
more readily and cheaply than the corresponding mono- and di-
arylphosphines. The mono- and di-arylphosphines are of
considerable interest, particularly as intermediates and also
as components of catalyst for many reactions. Their
possibilities have not been exploited, however, owing to their
relative inaccessibility and high price. By means of the
present invention, and by careful selection of reaction
conditions such as temperature and pressure, it is possible to
influence the relative amounts of mono-, d1- and tri-
arylphosphines produced.
The aryl compound can have only carbon atoms in the
ring, or can be heterocyclic containing one or more nitrogen,
oxygen or sulphur atoms. As nitrogen-containing compounds
there are mentioned, e.g. pyridine, pyrimidine, piperazine,
pyrazole. As an oxygen-containing heterocyclic compound there
is mentioned furan. As a sulphur-containing heterocyclic
compound there is mentioned thiophene. Examples of
hydrocarbyl aryl compounds include phenyl, a-naphthyl, p-
naphthyl, biphenyl, phenanthrenyl, anthracenyl, naphthacenyl
and 2,2'-bis(1,1'-binaphthyl) groups.
Preferred leaving groups are the halogens,
particularly chlorine, bromine and iodine. Other suitable
leaving groups include, for example, trifluoromethane-
sulfonyloxy, methanesulfonyloxy, toluenesulfonyloxy and
trifluoroacetate groups. The leaving group is attached to a
carbon atom of the aryl ring. The aryl compound can bear one
or more than one leaving group. Examples of aryl groups that
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bear two leaving groups, and therefore may bear two phosphorus
atoms after reaction, include the 1,2-phenyl group, the 1,4-
phenyl group, the 2,2'-biphenyl group of formula
and the 2,2'-bis(1,1'-binaphthyl) group of formula
The aryl halide is preferably an iodo- or a bromo-
compound. The aryl moiety can be unsubstituted or can be
substituted by groups that do not interfere with the reaction.
Such substituents include hydrocarbyl groups such as alkyl,
alkenyl and cycloalkyl groups. Mention is made of alkyl and
alkenyl groups, straight chained or branched, having up to
about 8 carbon atoms, cycloalkyl groups having from 3 to 8
carbon atoms and aryl groups such as phenyl or naphthyl,
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aralkyl groups such as benzyl or phenethyl and alkaryl groups
such as tolyl or xylyl groups. Other substituents include
aryl, acyloxy, alkoxy, alkenoxy and aryloxy groups, again
having up to about 8 carbon atoms. Particular compounds
include bromotoluenes, bromoxylenes, iodotoluenes and
iodoxylenes. The preferred aryl halides are bromobenzene and,
especially, iodobenzene.
As stated above, the aryl compound can bear
subst ituents that do not part icipate in the react ion with
phosphine. It is found that the reaction of the present
invention goes better with electron-withdrawing groups, for
instance trifluoromethyl, cyano, alkylcarbonyl and
alkoxycarbonyl. The substituted compounds that are of
greatest interest, however, are those that bear electron-
donating groups, for instance lower alkyl and lower alkoxy
groups. The aryl compound can bear one, two or more
substituents. To avoid steric interference it is preferred
that the substituents shall be in the 3-, 4- or 5- position,
relative to the leaving group. Mention is made of 3-
trifluoromethyl-phenyl, 4-trifluoromethylphenyl, 3-
cyanophenyl, 4-cyanophenyl, 3-acetylphenyl, 4-acetylphenyl, 3-
methoxycarbonylphenyl, 4-methoxycarbonylphenyl, 3-
acetoxyphenyl, 4-acetoxyphenyl, 3-methylphenyl, 4-
methylphenyl, 3,5-dimethylphenyl, 3-methoxyphenyl, 4-
methoxyphenyl and 3,5-dimethoxyphenyl groups, and also aryl
groups other than phenyl that are correspondingly substituted.
Phosphine is a gas under ambient conditions. The
reaction with the aryl compound is preferably carried out
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under elevated temperature and pressure. The product of the
reaction is a mixture of the mono-, d1- and tri-aryl
phosphines and the relative ratio of these three products
varies, depending upon the temperature and pressure of the
reaction, the amount of catalyst and the presence of a base as
promoter. The particular reaction conditions selected will
therefore depend upon the desired ratio of these products.
Elevated temperature, decreased pressure, a greater amount of
catalyst and a greater amount of base promoter all tend to
increase the amount of the di-aryl product at the expense of
the mono-. Temperatures from 70°C to about 150°C are
suitable, preferably from about 90 to 120°C. The pressure may
be in the range from ambient to about 600 psig.
The reaction is carried out in the presence of a
catalyst that is a metal of Group VIII of the Periodic Table,
or a compound of such a metal. Most suitable are the precious
metals of Group VIII, of which palladium is preferred.
Mention is made particularly of zero valence compounds of
palladium, examples of which include tetrakis(triphenyl-
phosphine)palladium, 1,2 bis(diphenylphosphine)ethane
palladium, dichlorobis(triphenylphosphine)palladium, 1,3-
bis(diphenylphosphine)-propane palladium, 1,4-bis(diphenyl-
phosphine)butane palladium and 1,1-bis(diphenylphosphine)-
ferrocene palladium.
Mention is made particularly of adducts of a Pd(II)
salt and a tertiary phosphine, especially 1:1 adducts as
catalysts. As palladium salts there are mentioned the
diacetate and the dichloride. The tertiary phosphine can be a
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trialkylphosphine, for instance, tri(ethyl)--, tri(propyl)-,
tri(n-butyl)-, tri(isobutyl)-, tri(cyclopentyl)-, ,
tri(cyclohexyl)- and tri(n-octyl)phosphine or a
triarylphosphine, of which triphenylphosphine and tri(ortho-
tolyl)phosphine are preferred. One preferred catalyst is an
adduct of palladium (II) acetate and tris(o-tolyl)phosphine
and is described (in German) by Wolfgang A. Herrmarin et al.,
in Angew. Chem., 1995, Volume 107, pages 1989-1992 and (in
English translation) in Angew. Chem. Int. Ed. Engl., 1995,
Volume 34, pages 1844-1848.
Mention is made also of palladium compounds that~are
standard rr donors, for instance Pd(cyclooctadiene]2,
Pd[cyclopentadiene]2 and Pd[dibenzylacetone]2.
The amount of catalyst can range from about 0.05
mole to about 10.0 mole percent, preferably from about 0.1 to
about 7.5 mole percent of the aryl compound initially charged..
It is possible to farm the catalyst and then add it
to the reaction vessel, or it is possible to add the
components of the catalyst, so that the catalyst is formed in
situ.
The reaction is preferably carried out in the
presence of a solvent. Suitable solvents include glyme, _.
acetonitrile, diethyl ether, anisol.e, di-n-butyl ether,
tetrahydrofuran, p-dioxane, toluene, xylene, cumene or a
mixture of toluene and isopropanol (e. g. a 3:1 mixture). Also
suitable are aliphatic, cycloaliphatic and aromatic
hydrocarbons, including hexane, heptane, octane, cyclohexane,
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benzene and petroleum fractions boiling at 70-140°C. Solvents
that have oxidising properties, such as DMSO, should be
avoided. Toluene is most preferred.
As stated above the reaction is preferably carried
out in the presence of a base promoter such as for example
sodium hydroxide, potassium hydroxide, sodium carbonate,
potassium carbonate, calcium carbonate, sodium bicarbonate,
potassium carbonate, sodium ethoxide, potassium ethoxide,
ammonium carbonate, ammonium bicarbonate, calcium oxide,
calcium hydroxide, magnesium oxide, magnesium hydroxide or the
like. Organic bases, particularly amines, can also be used.
Mention is made of pyridine and pyridine derivatives and
tertiary amines of which triethylamine, tributylamine, and
other trialkylamines are preferred.
The phosphine is supplied to a closed reactor under
pressure that is suitably in the range of from about 100 psig
to 600 psig, preferably about 200 psig to about 500 psig. The
temperature of the reactor is elevated to at least about 80°C
but does not usually exceed about 150°C. Preferably the
temperature is in the range of from about 100° to about 150°C.
The reaction time may be up to about 6 hours, after which the
reaction is quenched. Quenching is suitably carried out by
cooling. The reactions between the aryl compound and
phosphine do not proceed at reasonable rates much below about
90°C, so cooling the reaction mixture to below about 70 or
80°C is effective. Shorter reaction time and less base both
favour the production of mono-arylphosphine over d1- and tri-
arylphosphine, so these parameters can be varied in accordance
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with the desired product mixture.
The invention is further illustrated in the
following examples.
Example 1
Reaction of Iodobenzene with Phosphine at Low Pressure
A one litre toluene solution containing iodobenzene
(250 g, 1.23 moles), triethylamine (150 g, 1.5 moles) and
palladium dimer (1:1 adduct of palladium (II) acetate and
trio-tolyl)phosphine, 1.2 g, 1.28 mmole, 0.1 mole $, based on
numbers of moles of iodobenzene charged) was charged to a one
gallon autoclave under a nitrogen blanket. The solution was
maintained at 200 psig phosphine pressure and 100°C, with
stirring at 500 rpm, for 5 hours. The autoclave mixture was
then cooled to ambient temperature, vented and water (500 ml)
was added to dissolve the triethylamine hydriodide salt formed
during the reaction. The two liquid phases were discharged
from the autoclave and the toluene phase was analysed by
GC/FID. This phase was found to be composed of (relative
proportions were determined by area percent integration),
phenylphosphine (13~), diphenylphosphine (74~) and
triphenylphosphine (3~) as well as unreacted iodobenzene (10~)
and triethylamine. The total conversion of iodobenzene was
approximately 90~. The identity of all of these
arylphosphines was unambiguously established by both GC/MS and
phosphorus NMR techniques, by comparison with spectra of
authentic specimens of these materials.
Both phenylphosphine and diphenylphosphine were
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subsequently isolated in pure form by fractional distillation
under vacuum.
Example 2
Reaction of Iodobenzene with Phosphine at High Pressure
A one litre xylene solution containing iodobenzene
(375 g, 1.84 moles), triethylamine (150 g, 1.5 moles) and the
palladium dimer (1:1 adduct of palladium(II) acetate and
trio-tolyl)phosphine, 1.20 g, 1.2 mmole, 0.07 mole $) was
charged to a one gallon autoclave under a nitrogen blanket.
The solution was maintained at 500 psig phosphine pressure and
110°C, with stirring at 500 rpm, for 5 hours. At this time
the autoclave was cooled to ambient temperature, vented and
discharged as described above. Analysis of the xylene phase
by GC/FID (with area percent integration) gave only
monophenylphosphine (9~) and diphenylphosphine (7$), with no
sign of triphenyl-phosphine, for a total conversion of
iodobenzene of approximately 16~.
Subsequently, the monophenylphosphine present in the
mixture was completely converted to diphenylphosphine by
maintaining this xylene solution at 100°C for approximately 24
hours under a nitrogen blanket in the absence of phosphine.
Final conversion of diphenylphosphine to the triphenyl-
phosphine end product was observed to occur at a significantly
faster rate once the monophenylphosphine had been
substantially converted to diphenylphosphine.
Example 3
Reaction of 3-Trifluoromethyliodobenzene with Phosphine
A one litre toluene solution containing 3-trifluoro-
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methyliodobenzene (200 g, 0.73 mole), triethylamine (150 g,
1.5 moles) and palladium dimer (1:1 adduct of palladium (II)
acetate and trio-tolyl)phosphine, 0.69 g, 0.73 mmoles, 0.1
mole) was charged to a one gallon autoclave and maintained at
102°C and 200 psig phosphine pressure for 5 hours as described
above. A slight exotherm was observed during the first 30
min. of the experiment, which was controlled by means of
internal cooling. After isolating it as described above, the
organic phase was analysed by GC/FID and GC/MS and found to
contain mono (3-trifluoromethylphenyl)phosphine (15~), bis(3-
trifluoromethyl-phenyl)phosphine (59~) and tris(3-trifluoro-
methylphenyl)-phosphine (5~) in addition to the unreacted 3-
trifluoromethyl-iodobenzene (21~).
Example 4
Reaction of 3,5-Dimethyliodobenzene with Phosphine
A one litre toluene solution containing 3,5-
dimethyliodobenzene (161 g, 0.69 mole), triethylamine (150 g,
1.5 mole) and the palladium dimer (1:1 adduct of palladium
(II) acetate and trio-tolyl)phosphine 1.75 g, 1.8 mmole, 0.27
mole) was maintained at 105-110°C and 200 psig phosphine
pressure for 10 hours, then cooled, vented and discharged in
the usual manner. Analysis of the toluene phase by GC/FID and
GC/MS revealed the presence of mono (3,5-dimethylphenyl)-
phosphine (14~) and bis(3,5-dimethylphenyl)phosphine (12~)
with the remainder being unreacted 3,5-dimethyliodobenzene
(74~).
Example 5
Reaction of 1,4-Diiodobenzene with Phosphine
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A one litre xylene solution of 1,4-diiodobenzene
(150 g, 0.50 mole), triethylamine (100 g, 1.0 mole) and the
palladium dimer (1:1 adduct of palladium (II) acetate and
trio-tolyl)phosphine 0.5 g, 0.5 mmole, 0.1 mole) was
maintained at 110°C and 400 psig phosphine pressure for 6
hours, then cooled, vented and discharged in the usual manner.
Analysis of the xylene phase by GC/FID and GC/MS revealed the
presence of 4-iodophenylphosphine (17$), bis(4-
iodophenyl)phosphine (5~S) and 1,4-bis(phosphino)benzene (1%),
with the remainder being unreacted 1,4-diiodobenzene.
Analogously, 1,2-bis(phosphino)benzene can be
obtained from 1,2-diiodobenzene.
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