Note: Descriptions are shown in the official language in which they were submitted.
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TITLE: USE OF PHOSPHONIUM SALTS
FIELD OF THE INVENTION:
The present invention relates to phosphonium
salts, in particular their use as solvents for chemical
reactions and to methods of recovering reaction products.
BACKGROUND OF THE INVENTION:
Ionic liquids provide an attractive alternative to
traditional organic solvents for many chemical reactions.
Ionic liquids are non-flammable, have low vapour pressure,
high solvation abilities, are recyclable with low or no
waste and have high E factor and low cast factor. Reactions
in ionic liquids typically proceed under milder conditions
at rates that are comparable or much faster as compared to
conventional solvents. Also, as a result of their
distinctive physical and chemical properties, ionic liquids
can influence the stereoselectivity and regioselectivity of
reactions. For industrial purposes, the low vapour pressure
of ionic liquids is a very important feature. They are
essentially non-volatile, a property that eliminates many of
the containment problems typically encountered with
traditional organic solvents. Also, since many of the ionic
liquids are immiscible wits traditional organic solvents,
they offer a non-aqueous alternative to two-phase systems.
Hydrophobic ionic liquids can also be used as immiscible
polar phases with water.
Another important feature of ionic liquids is that
they are good solvents for a wide range of both inorganic
and organic compounds, and thus ionic liquids can be used to
bring inorganic reactants (e.g. inorganic catalysts) and
organic reactants into homogeneous solutions. The ability
to combine reagents to form homogeneous solutions is
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advantageous because reactions in homogeneous solutions are
inherently more efficient than reactions performed in
heterogeneous solutions. For example, when a catalytic
reaction is carried out in a homogeneous solution, all of
the metal centers of the catalyst are available to the
reagents. Indeed, startling differences in yields and
specificity have been seen between reactions in ionic
liquids as compared to traditional solvents. A recent
review of the properties and uses of ionic liquids is
provided in an article entitled "Room-Temperature Ionic
Liquids. Solvents for Synthesis and Catalysis," by Thomas
Welton CChem. Rev. 1999, 99, 2071-2083), the disclosure of
which is incorporated herein by reference.
Imidazolium salts find utility as ionic liquid
solvents. Imidazolium salts containing anions such as
tetrafluoroborate and hexafluorophosphate anions are
excellent solvents for many organic reactions. However,
some of the commonly used imidazolium salts, such as
3-butyl-1-methylimidazolium hexafluorophosphate, may not
support homogeneous reactions with nonpolar compounds, such
as saturated hydrocarbons, because these compounds are not
mutually miscible. For example, cyclohexane does not
dissolve in 1-butyl-3-methylimidazolium hexafluorophosphate.
Also, the miscibility of 1-pentene in 3-butyl-1-
methylimidazolium hexafluorophosphate ([bmim]-PF6) is poor,
and these two compounds exist in separate phases (see
Example 1 in U.S. Patent No. 5,852,130 and Example 1 in U.S.
Patent No. 6,040,263). Pentane would be even less miscible
with [bmim]-PF6 because pentane is less polar than 1-pentene.
Phosphonium salts may be used as ionic liquids and
have thermal stabilities that are comparable to or greater
than the corresponding imidazolium salts.
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SUMMARY OF THE INVENTION:
In one aspect the invention provides a homogeneous
mixture comprising a saturated hydrocarbon and a phosphonium
salt. The invention also provides the use of a phosphonium
salt as a solvent for a saturated hydrocarbon. The
invention further provides a method for making a homogeneous
solution comprising contacting a saturated hydrocarbon with
a phosphonium salt.
In another aspect, the invention provides a
homogeneous mixture comprising a metal catalyst, a saturated
hydrocarbon. and a phosphonium salt. The invention also
provides the use of a phosphonium salt as a solvent for
making a homogeneous mixture of a metal catalyst and a
saturated hydrocarbon. The invention further provides a
method for making a homogeneous solution comprising
contacting a saturated hydrocarbon and a metal catalyst with
a phosphonium salt.
In another aspect, the invention provides a
process for expelling a hydrocarbon, preferably a saturated
hydrocarbon, from a homogeneous mixture comprising the
hydrocarbon and a phosphonium salt ionic liquid, which
process comprises adding to the homogeneous mixture
sufficient water to cause the hydrocarbon and the
phosphonium~salt to form separate phases.
The invention further provides a three phase
liquid composition comprising a hydrocarbon phase, a
phosphonium salt phase, and a water phase.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE
INVENTION:
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Solvent polarity is commonly used to classify
solvents. A simple qualitative definition says that a polar
solvent is a solvent that will dissolve and stabilize
dipolar or charged solutes, and a nonpolar solvent is a
solvent that will dissolve nonpolar solutes. Since ionic
liquids are salts, it is widely considered that they will
provide highly polar solvents that will be suitable for
dissolving polar compounds. Accordingly, phosphonium salts
find utility as solvents for polar compounds. For example,
phosphonium salts can dissolve many metal catalysts and some
water.
It is an unexpected finding that ionic liquids
that have a tetrahydrocarbylphosphonium cation can dissolve
saturated hydrocarbons, which are nonpolar.
The solvent properties of phosphonium salts can be
affected by the presence of dissolved water. Addition of
water to a homogeneous mixture of a phosphonium ionic liquid
and a hydrocarbon may result in the formation of three
phases, namely, a lower water phase, an intermediate ionic
liquid phase and an upper hydrocarbon phase. These can be
separated for example, by decantation. For example,
addition of an effective amount of water to a homogeneous
solution of octane and trihexyl(tetradecyl)phosphonium
chloride causes separation of the system into three phases,
namely: the octane as the lightest phase; the phosphonium
salt ionic liquid as the intermediate phase; and water as
the heaviest phase.
It is possible that the separated ionic liquid
phase may still contain some hydrocarbon. This can be
removed by, for example, distillation or by one or more
further steps of addition of water. It is also possible
that the separated hydrocarbon phase may contain some ionic
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liquid, and one or more further steps of addition of water
can be carried out to separate the ionic liquid. The ionic
liquid thus obtained can be purified for example by vacuum
distillation at a temperature in the range from 60° to 90°C.
Ionic liquid has been used and recovered in this manner
three times, without any loss of activity.
The process for expelling a hydrocarbon from
solution by addition of water may not be confined to
saturated hydrocarbons, but may extend to aliphatic
hydrocarbons with a modest degree of unsaturation, say a
long chain olefin with only one double bond, for example
heptadecene. The ability to achieve separation upon
addition of water will depend on the properties of the
solute and the phosphonium salt and some unsaturated
hydrocarbons may react to the presence of water in a manner
similar to unsaturated hydrocarbons. Not all homogeneous
solutions of a hydrocarbon and a phosphonium salt may be
capable of separation by addition of water. For example,
addition of'water to a homogeneous solution of octene and
trihexyl(tetradecyl)phosphonium chloride does not cause
separation into three phases: the octene remains dissolved
in the phosphonium salt. However, the ability to achieve
separation by addition of water can be determined for any
particular combination of a phosphonium salt and a
hydrocarbon by routine experimentation, without the exercise
of any inventive faculty, because phase separation is
readily observed by eye.
To form a homogeneous mixture, little or no water
should be present in a mixture of a phosphonium salt and a
hydrocarbon, especially a saturated hydrocarbon. If
required, the water content of a phosphonium salt can be
reduced by, for example, vacuum stripping prior to admixing
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with the hydrocarbon. Vacuum stripping may be carried out
at elevated temperatures and under reduced pressure, for
example at 130-140° C and less than 50 mm Hg. The water
content of phosphonium salts thus treated can be reduced to
less than 1%, usually less than 0.2%. The phosphonium salt
can be kept under a dry or inert atmosphere to maintain low
moisture content. For certain applications, an inert
atmosphere will be preferred.
The fact that hydrocarbons, especially saturated
hydrocarbons, will dissolve in phosphonium ionic liquids
provides opportunities for carrying out reactions in the
ionic liquids as solvents. This is valuable as many metal
catalysts are soluble in the ionic liquids, although
reactions that are not catalysed and reactions that are
catalysed by heterogeneous catalysts and solid state
catalysts can take advantage of the solubility of the
hydrocarbons in the ionic liquid. In some instances the
product of reaction can be separated from the ionic liquid
by the addition of water, resulting in the formation of
three phases, as discussed above. In instances where
addition of water is not suitable the product can be
separated by other means, for example distillation. As
examples of reactions there are mentioned hydrogenation,
oxidation, and dimerization and oligomerization of olefinic
compounds, possibly in the presence of transition metal
catalysts. The property of miscibility of saturated
hydrocarbons can be helpful to carry out C-H activation (see
Periana et al., Science, 1998, 280, 560, incorporated herein
by reference).
The phosphonium salts are
tetrahydrocarbylphosphonium salts that can have a broad
range of phosphonium cations and a broad range of anions.
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There can be used phosphonium salts that have the general
formula (I):
R~ R2
Formula (~
R3~ ~ R4
wherein:
each of R1, R2, R3 and R4 is independently a
hydrocarbyl group; and
X- is an anion; suitable anions include, for
example, halides, phosphinates, alkylphosphinates,
alkylthiophosphinates, sulphonates, tosylates, aluminates,
borates, arsenates, cuprates, sulfates, nitrates, and
carboxylates, for example acetate, decanoate, citrate and
tartrate.
Tetrahydrocarbylphosphonium salts are preferred in
which each of R1, R2, R3 and R4 is independently an alkyl
group of 1 to 30 carbon atoms, a cycloalkyl group of 3 to 7
carbon atoms, an alkenyl group of 2 to 30 carbon atoms, an
alkynyl group of 2 to 30 carbon atoms, an aryl group of 6 to
18 carbon atoms, or an aralkyl group. It is possible for
two of R1, R2, R3 and R4 together to form an alkylene chain.
More preferred are phosphonium salts wherein at
least one of R1 to R' contains a higher number of carbon
atoms than the other of R1 to R4, for example 10 or more and
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preferably 14 or more. There is no theoretical upper limit
to the number of carbon atoms in each alkyl group, but it is
contemplated that usually each alkyl group will not have
more than 20 carbon atoms. Alkyl groups with 4 carbon atoms
or less can lead to an increase in the melting point of the
ionic liquid. Therefore, for many applications, more
preferred are phosphonium salts wherein each of Rl, R2, R3
and R4 is independently an alkyl group of 4 to 20 carbon
atoms. For example, R1, Rz, R3 and R4 may be n-butyl,
isobutyl, n-pentyl, cyclopFntyl, isopentyl, n-hexyl,
cyclohexyl, (2,4,4'-trimethyl)pentyl, cyclooctyl, tetradecyl,
etc. Usually the total number of carbon atoms present in
the phosphonium cation will not exceed 60, and preferably
will not exceed 55.
In many cases, it is desired that R1, Rz, R3 and R4
shall not all be identical, and that one of Rl, R2, R3 and R4
shall contain a significantly higher number of carbon atoms
than the others of R1, RZ, R3 and R4, Phosphonium salts in
which Rl, R2, R3 and R4 are not identical are referred to
herein as asymmetric. The degree of asymmetry and the
degree of branching of the hydrocarbyl groups are
determinants of the melting point of the phosphonium salt:
the melting point tends to decrease as the degree of
asymmetry and the degree of branching are increased.
Therefore, for many purposes, preferred compounds are those
in which R1, R2, R3 and R4 are not identical and/or are
branched. For many purposes, it is not necessary for the
phosphonium salt to be liquid at room temperature to
practice the current invention. Phosphonium salts that melt
at low temperatures, for example at temperatures less than
150° C and preferably less than 100° C, are suitable for
applications that are carried out at slightly elevated
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temperatures (i.e. above the melting point of the
phosphonium salt).
For many applications, phosphonium salts that are
water-immiscible will be preferred. The term "water
immiscible" is intended to describe phosphonium salts that
form a two phase system when mixed with water but does not
exclude phosphonium salts that dissolve in water nor
phosphonium salts that will dissolve water, provided that
the two phase system forms. Phosphonium salts that have a
large total number of carbons, for example equal to or
greater than 20 and in particular greater than 25 or 26, or
have at least one aryl group are more hydrophobic. Water
immiscibility is a desirable feature of phosphonium salts
because it facilitates isolation and recovery of the
phosphonium salt and any dissolved catalyst.
For many applications, phosphonium salts that are
less hygroscopic will be preferred. Phosphonium cations
that have a larger total number of carbons, for example
equal to or. greater than 30 carbons and especially greater
than 32 carbons, are more hydrophobic and less hygroscopic.
Some anions are hygroscopic, for example chloroaluminate.
Phosphonium salts include compounds according to
formula (I) wherein any of R1, R2, R3 and R4 is independently
an aryl or arylalkyl group. For example, one or more of Rl,
R2, R3 and R° may be phenyl, phenethyl, toluyl, xylyl, or
naphthyl.
It is possible for the groups R1, RZ, R3 and R4 to
bear substituents, or to include heteroatoms, provided that
the substituents or heteroatoms do not adversely affect the
desired properties of the compound. Acceptable substituents
include alkoxy, alkylthio, acetyl, and hydroxyl groups, and
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acceptable heteroatoms include oxygen and sulphur. Since
substituents and heteroatoms are likely to increase the cost
of the phosphonium compound, it is contemplated that, for
the most part, substituents and heteroatoms will not be
present.
X' can be any anion that can form a liquid salt at
temperatures below about 150° C with a cation described
above. Anions that form liquids at temperatures below about
100° C are more preferred, and those that form liquids below
about 80° C are still more preferred. Suitable anions
include, for example: halides, especially chlorides and
bromides; phosphinates; phosphates; mono- and
dialkylphosphinates, for example diisobutylphosphinate and
bis(2,4,4'-trimethylpentyl)phosphinate,
dicyclohexylphosphinate; alkylthiophosphinates, for example,
diisobutyldithiophosphinate; sulphonates; tosylates;
aluminates; borates; arsenates; cuprates; sulfates;
nitrates; triflates; bis(trifluoromethylsulfonyl)amides;
camphorsulfonates; perchlorates; citrates; tartarates;
phenoxides; alkoxides; tetrachlorometalates; C2 to C20
alkanoates and alkenoates, such as acetate, decanoate,
oleate, palmitate and stearate; perfluoroalkanoates;
tetrafluoroborates; hexafluorophosphates;
tris(trifluoromethylsulfonyl)methides and sulphur analogues;
hexafluorophosphate; hexafluoroantimonate;
hexafluoroarsenate; trifluoromethylsulphonate;
fluorosulphonate; tetrachloroaluminate; dichlorocuprate;
trichlorocuprate; tetrachlorocuprate; heptachloroaluminate;
decachloroaluminate; heptachloroaluminate; and
trichlorozincate.
The anion can have some effect on miscibility of
the phosphonium salt and saturated hydrocarbons. For
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example, anions that contain alkyl groups with a large total
number of carbon atoms will increase the hydrophobicity of
the phosphonium salt and may be preferred in some
applications. Of those anions that contain alkyl groups,
the alkyl groups each independently may have any of the
values given to R1 to R4 of the phosphonium cation (as
defined above ) .
Some of the phosphonium compounds of formula I are
novel. For example compounds with hydrocarbylphosphinate
and hydrocarbylthiophosphinate anions are novel and are the
subject of Canadian Patent Application Serial No. 2,343,456,
filed March 30, 2001. Novel compounds of formula I can be
obtained, for example from compounds of formula I in which
the anion is a good leaving group, for example a halide,
especially chloride or bromide, or sulfate by ion exchange
reaction with a corresponding salt containing the required
anion. Ammonium or alkali metal salts of the required anion
can be used for the ion exchange reaction.
The anion of the tetrahydrocarbylphosphonium salt
may affect the chemical properties, reactivity profile,
thermodynamic properties and physical properties of the
phosphonium salt ionic liquid. Therefore, certain anions
may be preferred for certain applications, as illustrated in
the following examples:
(i) Many of the phosphonium tetrafluoroborates and
hexafluorophosphates are liquids at room temperature and are
therefore suitable for room-temperature reactions.
(ii) For some applications, X- is preferably not a
halide. Halide ions, especially chloride ions, can
coordinate with some catalysts, for example catalysts
containing metals of group VIII of the periodic table (i.e.
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palladium), and reduce catalytic activity. Halide ions
should not be used where there is concern regarding reducing
catalytic activity, but can be used in other applications.
Phosphoniuim salts having halide ions can be used in the
preparation of ionic liquids having other anions, for
example acetate, trifluoroacetate, nitrate,
bis(trifluoromethylsulfonyl)imide and triflate ions. This
can be done by ion exchange, for example in acetone, with
stirring at 0° to 60° C.
(iii) Phosphinate,
tris(trifluoromethylsulfonyl)imide and triflate anions may
provide enhanced catalytic activity for some applications.
(iv) Moisture sensitive anions will not be
practical for some applications, especially those that
involve addition of water, for example to effect separation
of saturated hydrocarbons from the phosphonium salt.
Moisture sensitive anions include metal halides, for
example: tetrachloroaluminate, and transition metal halides
such as tetrachloroferrate, or trichlorocuprate.
(v) Trihexyl(tetradecyl)phosphonium
bis(trifluoromethylsulfonyl)imide has low viscosity and is
stable in the presence of 100% nitric acid, for example at
temperatures in the range of 20-80° C for a duration of at
least three days. Therefore, the
bis(trifluoromethylsulfonyl)imide anion may be preferred for
applications involving nitric acid or oxidants (such as
peroxides, molecular oxygen and air) and/or for applications
in which low viscosity is desirable.
(vi) Preferred anions for acid catalysis reactions
such as sulfonation, Friedel-Crafts alkylation, acylations
using super acidic acid catalysts (zeolite, metal triflates,
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metal triflamides, clays, etc.) include:
bis(trifluoromethylsulfonyl)imide and triflate.
The following list provides examples of preferred
phosphonium salts:
trihexyl(tetradecyl)phosphonium chloride;
tripentyl(tetradecyl)phosphonium chloride;
trioctyl(tetradecyl)phosphonium chloride;
trihexyl(tetradecyl)phosphonium bromide;
trihexyl(tetradecyl)phosphonium
bis(trifluoromethylsulfonyl)imide;
trihexyl(tetradecyl)phosphonium
dicyclohexylphosphinate;
trihexyl(tetradecyl)phosphonium tetrafluoroborate;
trihexyl(tetradecyl)phosphonium decanoate;
trihexyl(tetradecyl)phosphonium triflate;
trihexyl(tetradecyl)phosphonium
tris(trifluoromethylsulfonyl)imide;
trihexyl(tetradecyl)phosphonium
tris(trifluoromethylsulfonyl)methide; and
triisobutyl(tetradecyl)(methyl)phosphonium
tosylate.
Saturated hydrocarbons present in homogeneous
mixtures can be straight chained, branched, or cyclic
aliphatic molecules. There is no theoretical upper limit to
the number of carbon atoms in the saturated hydrocarbon.
However, saturated hydrocarbons with large numbers of carbon
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atoms exist in the solid phase at ambient temperatures, and
accordingly, slightly elevated temperatures (for example,
temperatures in the range of about 30-100° C) may be required
in order to dissolve a saturated hydrocarbon with a large
number of carbon atoms in a. phosphonium salt. The saturated
hydrocarbons may have as few as one carbon atom. There is
no particular upper limit on the number of carbon atoms, but
most interest is in those having up to about 20 carbon
atoms. Saturated hydrocarbon compounds containing a low
number of carbon atoms have low boiling points, so it may be
necessary to apply pressure in order to obtain homogeneous
mixtures of. the saturated hydrocarbon and phosphonium salt.
Examples of saturated hydrocarbons include alkanes
and cycloalkanes , for example: methane, ethane, propane,
isopropane, butane, isobutane, pentane, hexane, cyclohexane,
heptane, octane, nonane, and eicosane. The foregoing list
provides examples only and the invention is not restricted
to these compounds. Mixtures of hydrocarbons can of course
be used. Commercially available mixtures include "petroleum
ether" (b.p. 45°C to 60°C), which comprises a mixture of
butanes, pentanes and hexanes.
Homogeneous mixtures of saturated hydrocarbons and
phosphonium salts according to the current invention find
utility in reactions involving saturated hydrocarbons. For
example, saturated hydrocarbons in the homogeneous mixtures
can be reacted with activated halogen to produce alkyl
halides; the halogen may be activated by known methods known
in the art, for example light, heat, or a suitable catalyst
such as a ferric salt. The alkyl halides thus obtained can
be further substituted (i.e. functionalized) using any of a
number of substitution reactions known to those skilled in
the art. For example, alkyl halides may be converted to:
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alcohols by reaction with water (hydrolysis);
ethers by reaction with an alkali metal alkoxide,
such as sodium alkoxide;
amines by reaction with ammonia;
mercaptans by reaction with an alkali metal
sulfide, such as sodium sulfide; or
nitroalkanes by treatment with an alkali metal
nitrite, such as sodium nitrite.
The foregoing list of reactions is illustrative and is not
limiting. Examples of suitable reactions include
substitution of methane or ethane with a halogen followed by
hydrolysis to produce methanol and ethanol, respectively.
In many cases, the preferred process for recovery
of reaction products from the reaction mixture will be
distillation, especially under reduced pressure. Reaction
products can be isolated from the reaction mixture by
distillation because the vapour pressure of phosphonium salt
ionic liquids is extremely low. Distillation is suitable
for recovery of polar prodLCts such as methanol and ethanol.
In a further embodiment, a homogeneous mixture
comprising a saturated hydrocarbon and a phosphonium salt
may find utility as a stable reservoir for a hydrocarbon or
a mixture of hydrocarbons, especially for saturated
hydrocarbon gases or saturated hydrocarbons that have low
flash points. For example, a saturated hydrocarbon will
have a lower vapour pressure and therefore a lower flash
point when dissolved in a phosphonium salt. As a result, a
homogeneous mixture of a saturated hydrocarbon and a
phosphonium salt will be more easily contained and more
conveniently and safely shipped and handled than a pure
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saturated hydrocarbon. Thus, the phosphonium salt may find
utility as a stabilizer or flame retardant for saturated
hydrocarbons.
The current invention further provides a means of
extracting hydrocarbons from a source of hydrocarbons (such
as coal, oil sands (tar sands), or oil shale) into a
homogeneous solution. A phosphonium salt is contacted with
the source of hydrocarbons and hydrocarbons are extracted
into the phosphonium salt, thereby forming a homogeneous
mixture comprising hydrocarbons and phosphonium salt. The
resulting homogeneous mixture may comprise any hydrocarbons
that were contained in the source, including saturated and
unsaturated hydrocarbons as well as aromatic compounds.
Therefore, the homogeneous mixture may comprise a crude
extract of a mixture of hydrocarbons. The homogeneous
mixture can be separated from any remaining solid material,
for example by filtering. The extracted hydrocarbons may be
purified from the crude extract, for example by fractional
distillation. However, it may be desirable to use the crude
extract of hydrocarbons in phosphonium salt directly in
certain reactions, such as cracking. In either crude
extract or purified form, the extracted hydrocarbons find
utility in several commercially important reactions,
including catalytic hydrogenation (both addition
hydrogenation and destructive hydrogenation or
hydrogenolysis), cracking, gasification, methanation, and
various substitution and functionalization reactions, for
example halogenation.
The separation effected by addition of water may
rely on the ability of the phosphonium salt to dissolve
enough water to effect phase separation of the hydrocarbon.
The minimum~amount of water required to achieve phase
separation is readily observed by eye and may be as little
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as 5% w/v (water in phosphonium salt) or as much as 15% w/v
(water in phosphonium salt) and will depend on the
particular phosphonium salt and also on the particular
hydrocarbon, but it can be determined for any particular
salt and hydrocarbon by routine experimentation without
exercise of any inventive faculty. The amount of water
required to effect separation may be more than, the same as,
or less than the amount of water that can dissolve in the
particular phosphonium salt.
Phosphonium salts that are more hydrophobic, i.e.
contain a larger total number of carbon atoms, will dissolve
less water. Therefore, if phase separation is to be
achieved by addition of water, there may be an upper limit
to the total number of carbon atoms that may be present in
the phosphonium salt. Therefore, phosphonium salts wherein
the cation contains equal to or less than 60 and preferably
less than 55 carbon atoms are more preferred. More polar
phosphonium salts may require a smaller minimum amount of
water to be added to effect phase separation, even though
they are capable of dissolving larger quantities of water.
Addition of water in excess of the amount that can
be dissolved in a phosphonium salt that is immiscible with
water will result in formation of a new phase, namely an
aqueous phase. By way of illustration,
trihexyl(tetradecyl)phosphonium chloride becomes saturated
with water at about 10-15% w/v water content, and addition
of water in excess of this amount results in the formation
of a separate aqueous phase.
The separation effected by addition of water also
may rely on the properties of the hydrocarbon solute.
Hydrocarbons that are nonpolar or have a low degree of
polarity or are hydrophobic are more likely to be expelled
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from a phosphonium salt upon addition of water. Therefore,
saturated hydrocarbons are preferred. Also mentioned are
unsaturated hydrocarbons with a low degree of unsaturation
and a large number of carbon atoms, say 10 or more.
Examples of unsaturated hydrocarbons that may separate from
solution upon addition of water include: octene,
tetradecene, heptadecene, eicosene and eicodiene. Whether a
particular olefin will separate may depend upon the
particular phosphonium salt, as well as upon the olefin.
Separation of a hydrocarbon by addition of water
finds utility in recovering products of certain reactions.
Mention is made of the hydrogenation of unsaturated
hydrocarbons (including olefins, alkynes and arenes) to
produce saturated hydrocarbons. An unsaturated hydrocarbon
and a suitable metal catalyst (for example, palladium
acetate) are dissolved in a phosphonium salt solvent to
produce a homogeneous mixture. Hydrogen gas is supplied to
the reaction mixture and, upon completion of the reaction,
the saturated hydrocarbon reaction product can be recovered
by adding water to the reaction mixture, thereby causing the
saturated hydrocarbon reaction product to separate from the
solvent and form an upper phase that can be decanted and
thus isolated from the remaining reaction mixture. The
olefins can be monoolefins or diolefins, including
conjugated and unconjugated diolefins. Other compounds that
can be hydrogenated include acetylenic compounds, and
aromatic hydrocarbons (in particular, polynuclear aromatic
hydrocarbons). Examples of suitable olefins include:
butenes, pentenes, butadiene, isoprene, and 1,5-
cyclooctadiene.
Mention is also made of reactions in which olefins
are dimerized, oligomerized or polymerized and, if required,
subsequently hydrogenated to form higher alkanes. In a
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typical reaction, an olefin can be dimerized or oligomerized
and subsequently hydrogenated using standard transition
metal catalysis chemistry and phosphonium salt solvents, and
the higher alkanes produced can be recovered from the
reaction mixture by adding water to effect phase separation
and decanting the saturated hydrocarbon layer. For example,
butene can be dimerized and hydrogenated to obtain octane
and the octane can be recovered from the reaction mixture by
addition of water to effect phase separation. Or, isoprene
can be oligomerized to produce terpenes, which may be
recovered from the reaction mixture by addition of water to
effect phase separation.
For some applications, a suitable catalyst will be
dissolved in the phosphonium salt along with the hydrocarbon
reagent. However, solid-state catalysts and supported
catalysts may be used. Examples of catalysts for
hydrogenation of olefins can be found in U.S. Patent
5,852,130. These catalysts include zero-, mono-, di-, and
trivalent compounds in which the metal is selected from the
group consisting of Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, and Pt,
and can be bonded to a suitable ion, for example halide,
hexafluorophosphate, hexafluoroarsenate, tetrafluoroborate,
tetrachloroborate, or to a suitable hydrocarbon ligand such
as cyclopentadienyl and substituted cyclopentadienyl,
acetylacetonate and substituted acetylacetonate, or to a
suitable neutral ligand such as tertiary phosphine,
ditertiary diphosphine, phosphate, olefin, carbon monoxide,
or nitrile. These complexes may be mononuclear or
polynuclear, neutral, or ionic. They may contain a chiral
ligand.
EXAMPLES:
Exaanple 1:
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CA 02356709 2001-09-05
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6 ml of octane was added to 3 ml of
trihexyl(tetradecyl)phosphonium chloride at room temperature
under atmospheric pressure. A single phase was obtained,
consisting of a homogeneous mixture of the octane and
solvent.
1.2 ml of water were added to the octane/solvent
mixture with stirring. Stirring was stopped and the system
was allowed~to settle. The system settled into three
distinct phases: a lower aqueous phase, a middle
trihexyl(tetradecyl)phosphonium chloride phase, and an upper
octane phase.
The upper octane phase was decanted. Recovery of
octane was essentially quantitative.
The trihexyl(tetradecyl)phosphonium chloride phase
was then decanted and subsequently dried by vacuum stripping
at 130° C and about 50 mm Hg. The recovery of
trihexyl(tetradecyl)phosphonium chloride was essentially
quantitative.
Example 2:
1 g of octene was added to 1 g of
trihexyl(tetradecyl)phosphonium chloride at room
temperature, under atmospheric pressure. A single phase was
obtained, consisting of a homogeneous mixture of the octene
and solvent.
1 g of water was added to the octene/solvent
mixture with stirring. Stirring was stopped and the system
was allowed to settle. The system settled into two distinct
phases: a single upper phase consisting of octene and
trihexyl(tetradecyl)phosphonium chloride, and an aqueous
lower phase.
