Note: Descriptions are shown in the official language in which they were submitted.
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1
T 1781
PROCESS FOR THE PREPARATION OF ALCOHOLS
This invention relates to a process for the preparation of an
alcohol by hydrogenation of a carbonyl compound at elevated
temperature and superatmospheric pressure in the presence of a
homogeneous catalytic system.
Catalyst systems which have been proposed for this process,
include catalysts based on soluble Group VIII metal compounds, for
example of cobalt or rhodium.
Precursors for use in this process, such as aldehydes or
ketones may, for instance, be obtained by hydroformylation or
hydro-acylation of an olefinically unsaturated compound in the
presence of a Group VIII metal catalyst. The hydroformylation
process has attained industrial application and is also known as
the oxo process. Frequently, the aldehyde produced by
hydroformylation of an olefin is separated from the reaction
mixture obtained by the hydroformylation to eliminate the catalyst
and by-products and is subsequently used in the hydrogenation.
US-A-4 263 449 discloses a process for the preparation of
alcohols, wherein the aldehyde-containing reaction product of a
hydroformylation reaction is used as such in a subsequent
hydrogenation reaction catalysed by a heterogeneous Raney nickel or
cobalt catalyst. Water is added far generating a biphasic reaction
product facilitating separation of the catalysts used. Apart from
the inherent complications of the use of a plurality of catalysts,
the use of active Raney catalysts will concurrently hydrogenate any
olefin values remaining in the hydroformylation product.
According to GB-A-1 270 985, cobalt carbonyls modified by
tertiary phosphines, known to be active as hydroformylation
catalyst, can be used in the hydrogenation of aldehydes to alcohols
under an atmosphere comprising both hydrogen and carbon monoxide.
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However, high reaction temperatures and pressures are required for
this process.
US-A-3 876 672 discloses a process for the hydroformylation of
olefins to form aldehydes and alcohols using a catalyst comprising
a cationic hydride of Ni, Pd or Pt complexed with 2-4 monophosphine
ligands. Rather low conversions With low selectivities to alcohols
were observed.
Other known hydrogenation processes require a pure
hydrogenation atmosphere, so that carbon monoxide should be
removed, if an aldehyde-containing hydroformylation product is to
be directly used.
Therefore, there remains a continued need for improved and
more versatile catalysts for the hydrogenation of carbonyl
compounds.
It has now been found that the hydrogenation of aldehydes or
ketones to alcohols is advantageously effected in the presence of a
homogeneous catalytic system comprising a source of a Group VIII
metal compound and a bidentate phosphine.
The catalyst system used according to the invention offers the
advantages of high activity at mild conditions of temperature
and/or pressure, applicability in the presence or absence of carbon
monoxide in the hydrogenation atmosphere, and a remarkable
selectivity in that olefinically unsaturated compounds remain
substantially unaffected under conditions where the carbonyl
compounds are readily hydrogenated to alcohols.
It is also remarkable that the present invention allows for
hydrogenation of hindered ketones, i.e. ketones having at least one
secondary or tertiary alkyl group linked to the ketogroup, at high
rates.
It is remarked, that a catalytic system comprising a compound
of palladium and a bidentate phosphine is described by Y. Ben-David
et al., in J.Am.Chem.Soc., 1989, 111, 8742-4, but only for use in
the carbonylation of aryl chlorides.
Carbonyl compounds used as percursor in the present process
include aldehydes and ketones.
Y
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Aldehydes which are used for the hydrogenation are preferably
aliphatic aldehydes having 2-20 carbon atoms. They may contain one
or more aldehyde groups, and also substituents which are inert
under the reaction conditions, such as aryl groups, hydroxy groups,
carboxy groups, C1-4 alkoxy groups, or ester groups having
1-7 carbon atoms. Aldehydes having 3-20 carbon atoms which have ,
been prepared by oxo synthesis are particularly suitable. Suitable
examples include propanal, butanal, 2-methylpropanal,
4-hydroxybutanal, 6-oxohexanoic esters, octanal, nonyl aldehydes,
tridecanals or 2-ethylhexanal.
Ketones which are used for the hydrogenation are preferably
aliphatic ketones having 3-20 carbon atoms. They may contain one or
more ketogroups, and also inert substituents such as mentioned
above. Typical ketones include methyl iso-propylketone, ethyl
iso-propylketone and dicyclohexyl ketone.
The hydrogenation is carried out in the presence of a
catalytic system comprising a Group VIII metal which is preferably
selected from palladium, platinum, and rhodium, and most preferably
is palladium.
The Group VIII metal catalyst component may be provided in the
form of a Group VIII metal salt such as salts of nitric acid;
sulphuric acid; sulphonic acids, for example trifluoromethane
sulphonic acid or paratoluene sulphonic acid; and carboxylic acids,
for example acetic acid or trifluoro acetic acid. The Group VIII
metal salt may be in the form of a complex, for example with a
phosphine and/or other ligand. The Group VIII metal may also be
provided in the form of the metallic element or a zero valent
complex with a ligand such as a phosphine or carbon monoxide. If
provided in metallic form, it should be used with a protonic acid
for formation in situ of a soluble salt or complex.
The quantity of the Group VIII metal is not critical.
Preferably, it is in the range of 10'~ to 10-1 gram atom of Group
VIII metal per mole of aldehyde substrate, more preferably from
10-6 to 10 2.
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The second essential component of the catalytic system to be
used according to the invention is a bidentate phosphine. In the
present context, a bidentate phosphine is intended to cover any
organophosphorus compound having at least two phosphine groups and
being free of steric hindrance preventing coordination of two
phosphine F atoms to a single metal atom. The presence of further
coordinating or non-coordinating phosphine groups is not excluded.
Preferred bidentate phosphines to be used according to the
present invention have the formula,
R1R2P-X-PR3R4 (I),
wherein Rl, R2, R3 and R4 independently represent an optionally
substituted hydrocarbyl group, or Rl and R2 together and/or R3 and
R~' together represent an optionally substituted bivalent
hydrocarbyl group, at least one of R1, R2, R3 and R4 being
aliphatic, and X represents a bivalent bridging group having from 2
to 8 atoms in the bridge. More preferably, each of R1, R2, R3 and
R4 independently represents an aliphatic group, such as a
substituted or unsubstituted optionally branched or cyclic alkyl
group, suitably having from 1 to 20 carbon atoms.
Preferred aliphatic groups are unsubstituted alkyl groups
which may be branched or cyclic and have from 1 to 10 carbon atoms,
more preferably from 1 to 5 carbon atoms. Examples of suitable
alkyl groups are methyl, ethyl, n-propyl, iso-propyl, n-butyl,
sec-butyl, iso-butyl, tert-butyl, cyclohexyl and n-hexyl. Preferred
alkyl groups have one or two alpha-hydrogen atoms, in particular
one alpha-hydrogen atom as in secondary alkyl groups. Most
preferred alkyl group are ethyl, i-propyl, n-propyl, s-butyl and
n-butyl. If together constituting a bivalent hydrocarbyl group, Rl
and R2 or R3 and R4 preferably represent an aliphatic bivalent
radical, such as an optionally substituted alkylene or
cycloalkylene group, for example hexamethylene or cyclooctylene.
When the alkyl or alkylene group is said to be optionally
substituted, it may be substituted by one or more substituents
which do not annihilate the catalytic activity of the system.
Suitable substituents include halogen atoms, alkoxy groups,
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haloalkyl groups, haloalkoxy groups, acyl groups, acyloxy groups,
amino groups, hydroxyl groups, nitrile groups, acylamino groups,
and aryl groups.
The bridging group represented by X is preferably a hydro-
carbon, an ether or a thioether residue. For example, the bridging
group may be an optionally substituted alkylene chain which is
optionally interrupted by one or more oxygen and/or sulphur atoms,
as in:
-CH2CH2-; -GH2CH2CH2-; -CH2CH2CH2CH2-; or -CH2CH20CH2CH2-.
The bridging group preferably contains from 2 to 6 atoms in
the bridge, more preferably from 3 to 5 atoms. For example, when
the bridging group is a propane or neopeiitane residue, the bridge
contains 3 atoms. Preferred bridging groups X include trimethylene,
tetramethylene, and 3-oxapentamethylene.
Examples of phosphines of formula I which may be used in the
process according to the invention are:
1,2-bis(di-n-butylphosphino)ethane,
1,3-bis(dimethylphosphino)propane,
1,3-bis(diethylphosphino)propane,
1,3-bis(di-i-propylphosphino)propane,
1,3-bis(di-n-propylphosphino)propane,
1,3-bis(di-i-butylphosphino)propane,
1,3-bis(di-n-butylphosphino)propane,
1,3-bis(di-s-butylphosphino)propane,
1,3-bis(di-t-butylphosphino)propane,
1,3-bis(di-n-hexylphosphino)propane,
1,2-bis(dicyclohexylphosphino)ethane,
1,3-bis(n-butylmethylphosphino)propane,
1,3-bis(n-butylethylphosphino)propane,
1,3-bis(cyclooctylenephosphino)propane,
1,4-bis(di-i-propylphosphino)butane,
1,S-bis(dimethylphosphino)-3-oxapentane,
1,8-bis(di-n-butylphosphino)-3,6-dioxaoctane, and
1,4-bis(di-n-butylphosphino)-2,2,.,3-tetramethylbutane.
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Chiral phosphine ligands may be used if it is aimed at
obtaining chiral alcohols when hydrogenating asymmetric ketones, in
particular hindered ketones.
The ratio of the number of moles of the phosphine of formula I
per gram atom of Group VIII metal is preferably in the range of
from 0.5 to 10, more preferably from 0.9 to S, especially from
1 to 3.
It is preferred that the catalytic system to be used in the
process of the invention comprises the Group VIII metal in cationic
form, The required anion may be generated in situ, or, preferably,
is provided as component of the catalyst system. The source of an
anion is preferably a protonic acid. However, it may also be a salt
of the Group VIII metal, e.g. of palladium. It may also be a salt
of another metal, for example vanadium, chromium, nickel, copper or
silver, or a salt obtained by addition of a base, such as an
aromatic ~1-heterocycle, as in pyridinium salts.
Preferably the anion is a non- or weakly-coordinating anion:
that is to say an anion which does not or only weakly coordinates
with the palladium cation. It is preferably derived from a strong
acid having a pKa < 2, more preferably a pKa < - 1 (measured at
18 °C in aqueous solution). Since halide anions, in particular
chloride anion, tend to coordinate fairly strong to palladium, the
anion preferably is derived from strong acids except hydrohalogenic
acids.
For example, the anion may be derived from nitric acid;
sulfuric acid; a sulphonic acid such as fluorosulphonic acid,
chlorosulfonic acid, methanesulphonic acid, 2-hydroxypropane-
sulphonic acid, t-butylsulphonic acid, p-toluenesulphonic acid,
benzenesulphonic acid, trifluoromethanesulphonic acid, or a sulpho-
nated ion exchange resin; a perhalic acid such as perchloric acid;
or an acid derived by the interaction of a Lewis acid, such as BF3,
PFS, AsFS, SbFS, TaF~ or :lbFS, with a Broensted acid, such as HF
(e. g. fluorosilicic acid, HBF4, HPF6, HSbFS).
It will be appreciated that when using a palladium salt of a
weak acid, such as acetic acid, the addition of a strong acid such
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-,_
as a sulphonic acid will generate a salt of palladium with the
stronger acid, and the weak acid.
The phosphines of formula I as such are known compounds, and
can be prepared by general methods described in the literature, for
example Houben-Weyl, Vol. XII/I, p.21.
The catalyst system according to the invention may be
constituted in a liquid phase. The catalyst system is preferably
used in homogeneous mixture with the liquid phase of the reaction.
It is also possible to use the catalyst system in pseudo-hetero-
genized ~orm, for example an adsorbed liquid on porous carrier
surfaces. It is not necessary to use a separate solvent in the
process according to the invention. The starting aldehyde or ketone
and the alcohol product can often ~orm a suitable liquid phase. In
some cases, however, it may be desirable to use a separate solvent.
Any inert solvent can be used for that purpose. Representative
suitable solvents include hydrocarbons, suiphoxides, sulphones,
ethers, esters, ketones, alcohols, and amides. The reaction may be
conducted in the gaseous phase.
Conveniently, the aldehydas are hydrogenated in the reaction
mixture in which they are obtained, for example in the
hydroformylation.
Accordingly, the same catalyst can be used for both the
preparation of an aldehyde by hydroformylation, and subsequent
hydrogenation to the corresponding alcohol. Under reaction
conditions of fast hydroformylation and slow hydrogenation, the
aldehyde may be produced at high concentration in the reaction
mixture, from which it could be isolated, if desired. By adapting
the reaction conditions to fast hydrogenation, for example by
raising the temperature or increasing the hydrogen partial
pressure, the intermediate aldehyde is further reacted to the
alcohol in the same liquid reaction phase.
By appropriate choice of reaction conditions of fast
hydrogenation the alcohol may directly be prepared using the
aldehyde precursor olefinically unsaturated compound as starting
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_8_
material. The aldehyde initially formed then is immediately
consumed in the hydrogenation reaction to form the alcohol.
The process according to the invention is conveniently
effected at a temperature in the range of from 20 °C to 200 °C,
in
particular from SO °C to 150 °C.
The process according to the invention is preferably effected
at a total pressure of from 1 to 80 bar. Pressures higher than
100 bar may be used, but are generally economically unattractive on
account of special apparatus requirements. A pure hydrogen
atmosphere may be used for the hydrogenation, or the hydrogen
atmosphere may comprise inert diluent gases. For example, an
atmosphere comprising hydrogen and carbon monoxide may be used.
The process according to the invention may be carried out
batchwise. Industrially, however, it is advantageous to carry it
out continuously.
The alcohols produced by the process of the invention find
application as chemical solvent or as precursor for various
chemicals.
The invention will now be illustrated by the following
Examples.
Example 1
A 250 ml magnetically-stirred autoclave was charged with 20 ml
propanal, 40 ml diglyme (2,5,8-trioxanonane), 0.25 mmol of
palladium acetate, 0.3 mmol of 1,3-bis(di-i-propylphosphino)propane
and 1 mmol p-toluenesulphonic acid. After being flushed, the
autoclave was pressurised with 60 bar of hydrogen. The autoclave
was sealed, heated to a temperature of 90 °C, and maintained at
that temperature for 15 minutes, whereupon a sample of the contents
of the autoclave was analysed,by gas liquid chromatography (GLC).
From the results of the analysis it appeared that the propanal had
been completely converted into 1-propanol with a selectivity close
to 100. An average rate of conversion of 3900 mol of propanal per
gram atom of palladium per hour was observed.
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Examples 2-4
Example 1 was repeated, except for using the phosphines and
anion sources in the amounts and for the reaction times mentioned
in Table 1 below. The observed conversions of propanal (8), rates
of conversion (mol/gr.at.Pdjhr), and selectivities to 1-propanol
($) are reported in the Table.
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Table 1
Ex. Gr.VIIIligandl)anion2)time convey-cony. ~lec-
No. metal source sion rate civity
(mmol) (mmol) (mmol) (hr)
1 Pd0Ac2 iPrPC3 pTSA 0.25 100 3900 99
(0.25) (0.3) (1)
2 Pd0Ac2 iPrPC3 pTSA 0.25 98 3900 99
(0.25) (0.3) (1)
TFAcOH
(1)
3 Pd0Ac2 iPrPC3 TFMSA 0.25 100 3400 99
(0.25) (0.6) (1)
4 Pd0Ac EtPC3 pTSA 1.5 100 900 99
2
(0.25) (0.3) (1)
1) iPrPC3: 1,3-bis(di-i-propylphosphino)propane;
EtPC3: 1,3-bis(diethylphosphino)propane;
2) pTSA: p-toluene sulphonic acid; TFAcOH: trifluoro acetic acid;
TFMSA: trifluoromethylsulphonic acid; PhPA: benzenephosphonic
acid
Example 5
A 250 ml magnetically-stirred autoclave was charged with 20 m1
a-octene, 40 ml diglyme (2,5,8-trioxanonane), 0.25 mmol of
palladium acetate, 0.6 mmol of 1,3-bis(di-i-propylphosphino)propane
and 1 mmol t-butylsulphonic acid. After being flushed, the
autoclave was pressurised with carbon monoxide and hydrogen up to a
partial pressure of 30 bar of each. The autoclave Was sealed,
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heated to a temperature of 70 °C, and maintained at that
temperature for 7 hours, whereupon GLC of a sample of the contents
of the autoclave showed that 80~ of the ac-octene had been converted
into nonyl aldehydes, of which 888 were linear and 123 were
S branched.
After cooling the autoclave was flushed, and was then
pressurised with 60 bar of hydrogen and heated at 90 °C for
hours. GLC analysis showed a 100 conversion of nonyl aldehydes
into the corresponding nonyl alcohols at an initial rate of
conversion above 300 mol/gr at Pd/hr. The residual octenes
remaining after the hydroformylation step, appeared to be
substantially unchanged during the hydrogenation, with only 6~
being hydrogenated.
Example 6
a, A 250 ml magnetically-stirred autoclave was charged with 20 ml
a-octene, 40 ml diglyme, 0.25 mmol of palladium acetate, 0.6 mmol
of 1,3-bis(di-i-propylphosphino)propane and 1 mmol p-toluene-
sulphonic acid. After being flushed, the autoclave was pressurised
with carbon monoxide and hydrogen up to a partial pressure of
30 bar of each. The autoclave was sealed, heated to a temperature
of 90 °C, and maintained at that temperature for 5 hours, whereupon
GLC analysis of a sample of the contents of the autoclave showed
that 67$ of the a-octene had been converted with a selectivity of
94$ into nonyl aldehydes and S$ into the corresponding nonyl
alcohols.
b. The procedure under a. of this Example was repeated charging
the autoclave with 15 ml of a-octene and the same solvent and
catalytic system. The autoclave was pressurised with 20 bar of
carbon monoxide and 40 bar of hydrogen, and heated at 12S °C for
5 hours. GLC analysis showed that 63$ of the a-octene had been
converted with a selectivity of 888 into nonyl alcohols and 9$ into
nonyl aldehydes.
It is seen that using the same catalytic system the aldehyde
is formed as the predominant product under a., whereas at higher
hydrogen pressure and higher temperature the alcohol is the
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predominant product under b.. Apparently, in both experiments the
aldehyde is formed in a first reaction step and subsequently
consumed as a starting material for the second hydrogenation step,
under a. at relatively low rate and under b. at relatively high
rate under conditions of temperature and hydrogen concentration
favourable for hydrogenation.
Example 7
Following generally the procedure of Example 6b., a 250 ml
magnetically-stirred autoclave was charged with 20 ml a-dodecene,
40 ml diglyme, 0.25 m.-nol of palladium acetate, 0.6 mmol of
1,3-bis(1,S-cyclooctylenephosphino)propane, 1 mrnol p-toluene-
sulphonic acid and 1 mmol trifluoro acetic acid. The autoclave was
pressurised with 20 bar of carbon monoxide and 40 bar of hydrogen,
and heated at 12S °C for 5 hours. It was found that 62~ of the
a-dodecene had been converted with a selectivity of 98$ into
tridecyl alcohols and traces of the corresponding aldehydes.
Example 8
As in the previous Example, a 250 ml magnetically-stirred
autoclave was charged with 30 ml of a mixture of internally
unsaturated C14 olefins, 40 ml diglyme, 0.5 mmol of palladium
acetate, 1.2 mmol of 1,3-bis(di-i-propylphosphino)propane, 2 mmol
p-toluenesulphonic acid and 1 mmol trifluoro acetic acid. The
autoclave was pressurised with 20 bar of carbon monoxide and 40 bar
of hydrogen, and heated at 15S °C for 10 hours. It was found that
71$ of the C14 olefins had been converted with a selectivity of 98~
into pentadecyl alcohols.
Example 9
As in the previous Example, a 250 ml magnetically-stirred
autoclave was charged with 20 ml cyclohexene, 50 ml diglyme,
0.25 mmol of palladium acetate, 0.6 mmol of 1,3-bis(dimethyl-
phosphino)propane, 1 mmol trifluoro acetic acid and 1 mmol
p-toluenesulphonic acid. The autoclave was pressurised with 20 bar
of carbon monoxide and 40 bar of hydrogen, and heated at 130 °C for
S hours. It was found that 6$ of the cyclohexene had been converted
with a selectivity of 99$ into cyclohexylmethanol.
- 13
Example 10
As in the previous Example, a 250 ml magnetically-stirred
autoclave was charged with 20 ml styrene, 50 ml diglyme, 0.25 mmol
of palladium acetate, 0.6 mmol of 1,3-bis(di-i-propylphosphino)- ,
propane and 1 mmol p-toluenesulphonic acid. The autoclave was
pressurised with 20 bar of carbon monoxide and 40 bar of hydrogen,
and heated at 125 °C for 5 hours. It was found that 90$ of the
styrene had been converted with a selectivity of 85$ 3-phenyl-1-
propanol and 158 into 2-phenyl-1-propanol.
Example 11
As in the previous Examples, an autoclave was charged with
10 ml ethyl isopropyl ketone, 30 ml 2-butanol as solvent, 0.25 mmol
palladium acetate, 0.3 mmol 1,3-bis(di-i-propylphosphino)propane
and 2 mmol tri-fluoromethane sulphonic acid. The autoclave was
pressurized with 50 bar of hydrogen and heated at 70 °C for
6 hours. It was found that 100$ of the ethyl isopropyl ketone had
been converted with a selectivity of 98~ into 2-methylpentanol-3.
Example 12
Example 11 was exactly repeated except for charging 20 ml
methyl ethyl ketone instead of ethyl isopropyl ketone, and 20 ml
instead of 30 ml of 2-butanol solvent. After 2 hours of reaction at
70 °C, 90$ conversion of methyl ethyl ketone with a selectivity of
about 98~ into 2-butanol was observed.
Example 13
As in the previous Example, an autoclave was charged with
10 ml methyl isopropyl ketone, 25 ml 2-butanol, 0.25 mmol palladium
acetate, 0.3 mmol 1,3-bis(di-i-propylphosphino)propane and 2 mmol
paratoluenesulphonic acid. The autoclave was pressurized with
50 bar of hydrogen and heated at 70 °C for 6 hours. It was found
that 60$ of the methyl isopropyl ketone has been converted with a
selectivity of 98$ into 3-methylbutanol-2.
