Note: Descriptions are shown in the official language in which they were submitted.
20572~2
Process for the preparation of water-soluble
diphosphines
The invention relates to the preparation of diphosphines
which are derived from biaryl compounds and are soluble
in water as a result of the presence of sulfonic acid
radicals in the molecule.
Complex compounds which contain, as the central atom, a
metal of group VIII of the periodic table of the elements
and, as ligands, P(III) compounds such as phosphines and
phosphites and in addition optionally other groups suited
for complex formation, have recently become increasingly
important as catalysts. Thus, the reaction of olefins
with synthesis gas to give aldehydes (hydroformylation)
practiced industrially on a large scale is carried out
in the presence of catalyst systems which are composed of
cobalt and, in particular, rhodium and triphenyl-
phosphine. Catalysts based on complex compounds contain-
ing phosphines have also proved suitable for the reaction
of methanol with synthesis gas to give higher alcohols,
in particular ethanol and propanol (homologization). In
accordance with the solubility of these catalysts in
organic media, the reactions are carried out in the
homogeneous phase.
Instead of in the homogeneous phase, the reactions can
also be carried out in heterogeneous reaction systems.
The advantage of this process variant is the simple and
gentle separation of the catalyst, which is present
dissolved in water, from the water-insoluble reaction
product. For example, the process described in
DE 2,700,904 C2 for the addition of hydrogen cyanide to
an unsaturated organic compound having at least one
ethylenic double bond works according to this principle.
Suitable catalysts for this reaction are the systems
nickel/TPPTS [TPPTS is tri(sulfophenyl)phosphine],
palladium/TPPTS or iron/TPPTS. For the preparation of
aldehydes by reaction of olefins with carbon monoxide and
hydrogen, according to the process of DE 2,627,354 C2
--- ~ *
- 2 - 2057252
`_
rhodium is employed in metallic form or in the form of
one of its compounds together with a water-soluble
phosphine, for example TPPTS, as the catalyst.
Diphosphines, which as bidentate ligands are able to form
chelates with metal ions, are only used rarely, in con-
trast to the monophosphines, and then exclusively as
constituents of homogeneously dissolved catalysts. Thus,
according to the teaching of DE 2,904,782 C2, aldehydes
are obtained by hydroformylation of a lower olefinic
compound in an organic solvent in the presence of a
rhodium complex, a trisubstituted monophosphine and a
diphosphinoalkane.
DE 2,909,041 Al describes a process for the preparation
of aldehydes by hydroformylation of olefins in which
platinum is present as the catalyst, the halide of at
least one metal of group IVB of the periodic table of the
elements ("carbon group") is present as the auxiliary
catalyst and a two-bonded ligand of the formula
R2X-Z-Y-Z-XR' 2 ( R or R' is an alkyl, aryl or aralkyl
group, X is phosphorus, arsenic or antimony, Y is an
al~ylene, arylene or aralkylene group and Z is a methy-
lene group or an oxygen atom) is present as the reaction
promoter. 2,2'-Bis(diphenylphosphinomethyl)-l,l'-
binaphthyl is used in combination with a rhodium or
nickel compound as a ligand for asymmetric hydrogenation
catalysts according to Laid-open Japanese Patent
Application 79/39,059.
A reason for the comparatively rare use of diphosphines
as a constituent of catalysts may be the difficulties
which stand in the way of their preparation on an
industrial scale. A number of laboratory processes for
obt~ining diphosphines are indeed known, but their
application to industrial production processes is not
without problems, either technically or economically.
A process which inter alia relates to the preparation of
2057252
- 3 -
diphosphines - they are used as bidentate phosphorus
ligands - is the subject of EP 0,326,286 Al. Biaryl
compounds are employed as starting substances which are
substituted in each of the two aryl groups by the radical
-CH(R3)(R4) and optionally by other radicals. They are
converted by the action of proton-eliminating reagents
into biaryldianions, which are reacted with phosphorus
compounds of the formulae X-P(Rl)~2) or X-PO(Rl)(R2) (X is
preferably a halogen atom). In this manner, diphosphines
are obtained directly or, if the phosphorus compound
X-PO(Rl)(R2) was employed, after reduction.
The process described above is suitable only for the
preparation of diphosphines which are not substituted or
contain substituents which are inert to compounds having
reducing action. In this connection, it has to be taken
into account that a reduction step is not only necessary
when using reactants of the type X-P(O)(Rl)(R2). The
formation of the biaryldianion also takes place under
reducing conditions, as the reagents employed for elimi-
nating the proton, such as alkali metal hydrides oralkali metal alkyls, have reducing action. A direct
preparation of biarylphosphines cont~ining sulfonic acid
groups is therefore not possible in the way described
above, because the sulfonic acid groups are not retained
in the reaction of biaryl and phosphorus compound.
The object was therefore to develop a process for the
preparation of sulfonated diphosphines which not only
solves the problems described, but is also simple to
carry out industrially and moreover economical.
The object described above is achieved by a process for
the preparation of water-soluble diphosphines. It
comprises treating biaryl compounds of the formula (I)
20572~2
_ - 4 -
(A)2P\ P(A)2
(H2C)m (CH2)m
(R )n (R )n
(I)
in which A is identical or different and is alkyl,
cycloalkyl, phenyl, tolyl or naphthyl radicals, Rl is
identical or different and is hydrogen or alkyl or alkoxy
radicals having 1 to 14 carbon atoms, furthermore cyclo-
alkyl, aryl or aroxy radicals having 6 to 14 carbon atomsor a fused benzene ring, m is identical or different and
is an integer from 0 to 5 and n is likewise identical or
different and is integers from 0 to 4, at temperatures
from 0 to 60C with a solution of sulfur trioxide in
sulfuric acid and then allowing the mixture to react
subsequently with vigorous stirring at 20 to 60C, in
particular 20 to 30C, over a period of 1 to 60 h,
diluting the reaction mixture with water while
maint~ining a temperature of from 0 to 20C, in
particular 0 to 10C, followed by working up.
It is surprisingly possible by the process according to
the invention to sulfonate biaryls substituted by di-
organoalkylenephosphine groups under mild conditions
(where organo is an abbreviation for alkyl, cycloalkyl,
phenyl, tolyl or naphthyl radicals). It is particularly
remarkable that the formation of oxidation products such
as phosphine oxides is largely suppressed. The progress
of the sulfonation can be monitored and checked in a
simple manner by 3lP-NMR spectroscopy.
The biaryls employed as starting compounds in each case
contain a -(CH2)mP(A)2-radical in the 2- and 2'-position.
- 5 - 2057252
A and m in this case have the meanings described above.
A is preferably a phenyl, tolyl or naphthyl radical. The
biaryl molecule can furthermore be substituted by one or
more identical or different radicals R1. The meaning of R1
is described above. R1 is in particular hydrogen, a
methyl, isopropyl, isobutyl, t-butyl, phenyl or naphthyl
radical or a fused benzene ring. m is preferably 1 and n
is 0 or 1.
Sulfonated biaryl derivatives which are substituted in
the 6- and 6'-position by R1 radicals (excepting fused
benzene ring from the meaning) are of particular sig-
nificance. Their presence prevents the rotation of the
two substituted phenyl radicals. Complex compounds which
contain molecules of this type as ligands can therefore
be employed as catalysts for enantioselective reactions.
For the preparation of the biaryl derivatives cont~ining
phosphorus, the biaryls on which they are based are
advantageously used as starting materials.
The biaryls are obtained according to prior art pro-
cesses, for example by coupling aryl Grignard reagentswith aryl chloride, bromide or iodide in the presence of
nickel catalysts. Another route to obtain them is the
dehalogenation of aryl bromides and iodides in the pres-
ence of powdered active nickel oxides.
For the introduction of the phosphine radical into the
biaryl and thus for the preparation of the intermediate
for obtaining the sulfonated compound, a novel procedure
which starts from easily accessible starting substances
has proved very suitable. It comprises the reaction of
2,2'-dilithiobiphenyl or its derivatives of the formula
(Rl)n (R )n
.~ ~
Li Li
- 6 - 2057252
-
with a diarylphosphine halide of the formula (A)2P(CH2)mX
(where in the formulae R1, A, m and n have the meanings
described above and X is halogen). For the reaction, the
two reactants are suspended in stoichiometric amounts or
with a small excess of one of the two components in an
inert organic solvent, for example an aliphatic
hydrocarbon or hydrocarbon mixture such as hexane or
light petroleum, in an aromatic hydrocarbon such as
toluene or in an ether such as tetrahydrofuran, and the
mixture is stirred at temperatures of from -50 to 100C,
preferably from -20 to 50C. The reaction product
dissolved in the organic medium is hydrolyzed using
water. The diphosphine can be obtained in high yields
from the organic phase after removal of the solvent by
distillation and an optionally added purification step.
The diphosphine can be employed for the sulfonation
without prior purification. The sulfonating agent used
according to the invention is oleum, i.e. a solution of
S03 in sulfuric acid. It is advantageous to employ oleum
having an S03 concentration of 20 to 65 % by weight,
relative to the solution. An essential feature of the
novel procedure is the maintenance of specific reaction
temperatures. These are 0 to 60C and low temperatures
in the range from 0 to 20C are preferred. In order to
ensure that the temperature ranges mentioned are not
exceeded, it is recommended that the diphosphine is first
dissolved in concentrated sulfuric acid and the solution
is then treated with oleum in portions with stirring and
intensive cooling. It is then allowed to react with
vigorous stirring at 20 to 60C, in particular 20 to
30C, over a period of 1 to 60 h. S03 concentrations in
the oleum and the period of stirring determine the degree
of sulfonation of the diphosphine. The higher the supply
of S03 and the longer the mixture is stirred, the more
sulfonic acid groups enter the diphosphine molecule. As
soon as the reaction is complete, the reaction mixture is
worked up by dilution with water. There are several
processes available for this. According to an approved
_ 7 _ 2057252
procedure, the sulfuric acid solution is first neutral-
ized. Both during dilution of the reaction mixture and
during neutralization, care is to be taken that over-
heating does not occur and it has proved suitable to
maintain temperatures of from 0 to 20C, in particular
from 0 to 10C. The aqueous solution of an alkali metal
hydroxide, preferably sodium hydroxide, is used for
neutralization. Alkali metal hydroxide concentrations of
20 to 60 % by weight, relative to the solution, have
proved suitable. In order to achieve precipitation which
is as complete as possible of the alkali metal sulfate
formed from the sulfuric acid and alkali metal hydroxide,
it is recommended to work at not too great a dilution.
Alkali metal sulfate precipitates from the neutralized
reaction mixture. It is filtered off and washed several
times with a lower alcohol, preferably a C1- to C4-
alcohol, in particular methanol. The sulfonated di-
phosphine is obtained from the filtrate by removal of the
solvent under mild conditions, for example by distil-
lation in the vacuum of an oil pump. For purification,the crystalline product obtained is dissolved in a little
water, the solution is mixed with a lower alcohol,
preferably a C1- to C4-alcohol, in particular methanol,
and filtered, and the solvent is again removed gently.
According to another process, the subject of European
Patent 0,107,006, the acidic aqueous solution of the
sulfonation product is extracted with the solution of a
water-insoluble amine in a water-insoluble organic
solvent. The organic phase is removed and brought into
intimate contact with the aqueous solution of a base. The
sulfonated diphosphine can then be isolated from the
aqueous phase removed.
The sulfonated diphosphines are colorless to yellowish-
colored powders. Depending on the sulfonation conditions,
they contain 4 to 6 sulfonic acid groups. They dissolve
very easily in water and the solubility is 0.5 to 1.5 kg
of sulfonation product/l of water according to the degree
- 8 - 2057252
of sulfonation. The free acids and also the salts of
other metals can be prepared from the alkali metal salts,
for example by ion exchange.
The novel process is illustrated in the subsequent
example, but it is not restricted to the embodiments
described.
ExamPle
1. Preparation of 2,2'-bis(diphenylphosphino~ethyl)-
biphenyl ("BISBI")
2.34 g (10 mmol) of ClCH2PPh2, obtained according to
Langhans et al., Chem. Ber. 123 (1990), 995-999, are
suspended in 30 ml of hexane in a 250 ml three-necked
flask provided with a reflux condenser, dropping funnel
and magnetic stirrer and treated dropwise with vigorous
stirring with a suspension of 0.83 g (5 mmol) of 2,2'-
dilithiobiphenyl, obtained according to J. Organomet.
Chem. 228 (1982), 107-118, in 30 ml of hexane. The
mixture is then heated at 60C for about 30 min and the
solution is cooled by addition of 2G ml of toluene. After
stirring for 20 minutes, it is cautiously hydrolyzed with
10 ml of water. The organic phase is e,lloved in a separ-
ating funnel, washed three times with 5 ml portions of
water and freed of solvent in an oil pump vacuum at a
maximum of 30C. BISBI is precipitated from the residual
viscous oil as a white solid by addition of 15 ml of
ethanol and filtered off through a G3 glass frit.
Yield: 70 ~ of theory. The batch size can be increased
100-fold without disadvantages or losses in yield if
reaction vessels and reaction times are increased.
2. Sulfonation of BISBI
1 mmol of BISBI are dissolved in 2 ml of concentrated
sulfuric acid and treated dropwise at 0C with 5 ml of
- 9 - 2057252
oleum (S03 content: 20 to 65 % by weight, relative to the
solution). After warming to room temperature (about
20C), the reaction mixture is stirred vigorously for
several hours, then poured cautiously onto about 100 g of
ice and neutralized at temperatures below 5C using an
aqueous NaOH solution (NaOH content: 50 % by weight,
relative to the solution). The resulting suspension is
filtered and the filtrate is added to 25 ml of methanol.
The filter cake is washed twice with 25 ml portions of
methanol. The combined fractions are concentrated to
dryness in an oil pump vacuum and the residue is taken up
in very little water. The clear, amber-colored solution
is injected into 30 ml of methanol, the suspension is
stirred and filtered, and the filtrate is concentrated to
dryness in an oil pump vacuum. The sulfonation period
depends on the progress of the reaction, which is moni-
tored by 3lP-nuclear magnetic resonance spectroscopy at
intervals of about 2 h.
Characterization of the reaction product
The reaction product described below was obtained from
BISBI, after reaction for 17 h, by reaction with 65 %
strength oleum.
3lP-NMR (161.8 MHz, CD2Cl2, 20C): ~ = -6.8 (s), -7.1 (s),
-9.5 (s), -9.6 (s)
IR (KBr, cm1) ~ = 993 (m), 1040 (st), 1098 (m), 1127 (m),
1146 (m), 1195 (sst)
P/S ratio = 2 : 5.7 (elemental analysis)
Solubility: greater than 1 g/ml of water
Appearance: yellowish powder
