Note: Descriptions are shown in the official language in which they were submitted.
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Synthesis of organic phosphines
Field of the Invention
This invention relates to the synthesis of organic
phosphines.
Background of the Invention
It is known to react phosphine with a cyclooctadiene
to form a phosphabicyclononane.
U.S. Patent No. 4,163,760 (Elsner et al.) describes,
in Example 3, the reaction of a stoichiometric excess of
phosphine with 1,5-cyclooctadiene in toluene as solvent, at an
elevated pressure of 150 bars, in the presence of a free
radical initiator, azobisisobutyronitrile, to form a mixture
composed predominantly of the [3.3.1]- and [4.2.1]- isomers of
9H-9-phosphabicyclononane.
U.S. Patent No. 5,284,555 (Hoye et al.) describes, in
Example 12, the reaction of cyclooctadiene with phosphine to
form 22.3% 9-phosphabicyclo[3.3.1]nonane, 2.40 9-
phosphabicyclo[4.2.1]nonane, 10.4% of other secondary
phosphines, and 64.3% tertiary phosphine products. The
reaction is carried out by heating the reactants in the
presence of 2,2'-diazobis(2,4-dimethylvaleronitrile), a free-
radical initiator, without solvent.
However, one problem noted in the prior art is that
the reaction often produces not only the secondary phosphine
products that are desired, i.e. phosphabicyclononanes, but also
other secondary and tertiary phosphine products that are
undesired.
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Summary of the Invention
In one aspect this invention provides a process for
preparing a 9-phosphabicyclononane which comprises the addition
of phosphine to 1,5-cyclooctadiene in the presence of a free
radical initiator in a polar solvent.
Detailed Description of Preferred Embodiments of the Invention
The reaction of 1,5-cyclooctadiene with phosphine:
~"i 3
results in the formation of predominantly two isomers, 9-
phosphabicyclo[3.3.1]nonane and 9-phosphabicyclo[4.2.1]nonane,
designated as the A-, and B- isomers, respectively, as shown
below:
H H
p p
A-isomer B-isomer
The reaction also results in several unwanted side products
including 9-(cycloocten-4-yl)-9-phosphabicyclo[3.3.1]nonane and
9-(cycloocten-4-yl)-9-phosphabicyclo[4.2.1]nonane, designated
as the C-isomers, and di(cycloocten-4-yl)phosphine, designated
as the D-isomer as shown below:
3~ Q g ~~~
C-isomers D-isomer
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Carrying out the reaction in accordance with the
invention results in a much enhanced ratio of desired to
undesired products. As shown in the Examples below and in
Tables 1 and 2, the ratio of the desired isomers A and B versus
the undesired isomers C and D goes from approximately 8 to 12
to approximately 20 to 28 when the solvent is changed from a
non-polar to a polar solvent.
The reaction is initiated by free-radicals. The
source of such radicals may include the decomposition of a
radical-initiating compound to form free radicals, typically
thermally or by means of a source of radiation, such a UV
light. Such a free radical initiator can be, for example, a
peroxide or an azo radical initiator. Alternatively,
radiation, such as gamma radiation, can also be used on its own
as a free radical initiator.
Peroxides, for example dialkyl peroxides such as
di(tert-butyl)peroxide, and diacyl peroxides such as butyryl,
lauroyl, and benzoyl peroxides, tend to require higher reaction
temperatures compared with azo compounds, to initiate free
radical formation, and also tend to cause the formation of
phosphine oxide; so, their use is not preferred. Radiation on
its own is not preferred either, because phosphine is not a
good gamma radiation absorber, and the equipment required to
produce the radiation can be expensive.
The free radical initiator is preferably an azo
compound, such as 2,2'-azobis(2-methylisocapronitrile),
2,2'-azobisisobutyronitrile (VazoTM 64), 2,2'-azobis(2,
4-dimethylvaleronitrile) (VazoTM 52), 2,2'-azobis
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(2-methylbutyronitrile), also known as azobisisovaleronitrile
(VazoTM 67), 1,1'-azobis(cyclohexanecarbonitrile) (VazoTM 88),
and the like. The last four are available from Du Pont under
the trade-mark Vazo. As mentioned above, these azo compounds
decompose to yield free radicals that initiate the desired
reaction. Such decomposition may be initiated thermally or by
UV radiation. Different initiators, of course, decompose at
different temperatures and rates. The number following the
Vazo trade-marks listed above indicates the temperature at
which the compound has a half-life of 10 hours. Thus, Vazo 67
has a half-life of 10 hours at 67°C and Vazo 52 has the same
half-life at 52°C.
The process is carried out in a polar solvent.
Examples of polar solvents include DMF, aliphatic ethers, such
as diethyl ether and tetrahydrofuran (THF), aliphatic ketones,
such as acetone and methyl isobutyl ketone (MIBK), and
alcohols. It is preferred to carry out the reaction in an
alcohol or an ether, more preferably an alcohol. The alcohol
may be benzyl alcohol, but is preferably a branched or
unbranched saturated alcohol, preferably a C1_5 alcohol such as
butanol, more preferably a C1_3 alcohol, such as methanol,
ethanol, or isopropanol. The favoured alcohols are ethanol and
methanol. A mix of any of the above solvents may also be
employed. The ethanol may be denatured, preferably with a
polar denaturing agent such as methanol. For example, the
ethanol may be denatured with 15% methanol. Polar solvents
with oxidizing properties, such as dimethyl sulfoxide, are to
be avoided.
The process is preferably carried out in an inert
atmosphere, such as under nitrogen, argon, or helium, to
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prevent the desired products from being converted into their
oxidized forms, and because the phosphine is pyrophoric in the
presence of oxygen.
The process can be carried out at phosphine pressures
of 200 to 700 pounds per square inch (psig). However, when
carried out at lower phosphine pressure, there is greater
formation of unwanted products, such as the C and D isomers.
Thus, it is preferred to carry out the reaction at the highest
phosphine pressure the system can stand, generally about 500 to
700 psig.
The preferred temperatures at which the process is
carried out depends on the radical initiator used. When
radiation is used to form free radicals, the temperature
preferably ranges from 0 to 150°C, more preferably 15 to 70°C.
When an initiator is decomposed thermally to form free
radicals, the temperature depends on the half-life of the
initiator. The temperature is preferably chosen such that the
half-life of the initiator is 5 minutes to 1 hour, more
preferably 15 to 30 minutes.
The concentration of the reactants is not critical to
the working of the invention. However, it is not desirable to
use a highly concentrated solution of cyclooctadiene, so that
there forms a slurry that is so thick that it impedes the
reaction of the phosphine with the 1,5-cyclooctadiene and/or
the handling of the product. Preferable concentrations of the
cyclooctadiene in the polar solvent range from 1 to 20 M, more
preferably 2 to 12 M. The phosphine pressure is typically 200
to 700 psig, preferably 500 to 700 psig. When the radical
initiator is decomposed thermally, it is preferred that the
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amount of the initiator is about 0.0005 to 0.025 mols per mole
of cyclooctadiene.
The reaction between cyclooctadiene and phosphine is
usually exothermic. Thus, when an azo radical initiator is
used, it is preferable to add the radical initiator slowly and
with cooling to a solution of the cyclooctadiene in the
presence of phosphine, at a rate such that the temperature of
the reaction does not exceed the preferred ranges discussed
above.
Example 1
An autoclave, inerted with nitrogen was charged with
5308 (4.9 mols) of 1,5-cyclooctadiene and 11088 of methanol.
The reactor contents were heated to about 95°C under 600 psig
of phosphine pressure. Using a pressure pump, 118 (57 mmols)
Vazo 67 (2,2'-azobis(2-methylbutyronitrile)) dissolved in 200 g
of methanol was added over a period of 4 hours while the
temperature was maintained at about 95°C and the pressure was
maintained at about 600 psig with phosphine. When the reaction
was complete, the reactor contents were allowed to cool
somewhat before venting off excess phosphine. The reactor was
purged several times with nitrogen after which 1342.18 of
product (including both dissolved and undissolved products and
the solvent) were recovered as a slurry in methanol from the
reactor. Gas chromatographic analysis of the product mixture
indicated a product ratio of A and B isomers (desired) to C and
D isomers (undesired) of 28.376 to 1.
Examples 2 and 3
In a manner similar to that described in Example 1,
1,5-cyclooctadiene was reacted with phosphine using ethanol
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(Example 2) and isopropanol (Example 3) as solvents instead of
methanol. The respective charges, product mass, and product
ratio for Examples 1 to 3 are given in Table 1.
Comparative Examples 4 and 5
In a manner similar to that described for Examples 1
to 3, 1,5-cyclooctadiene was reacted with phosphine using
toluene and tri-butyl toluene (TBT) as solvents instead of an
alcohol. The charges, product mass, and product ratio for
Comparative Examples 4 and 5 are given in Table 2
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Table 1: Charges and Product Ratios as a Function of Solvent
for Examples 1 to 3.
Example: 1 2 3
solvent: Methanol Ethanol Isopropanol
Mass Charged
(g)
1,5 cyclo- 530 530.7 1036.9
octadiene
solvent 1108 1103.7 714.8
Vazo 67 in 11 11.2 17
2008 solvent
Product Data
Product Mass 1342.1 1820 2036.4
(g)
(A+B)/(C+D) 28.376 28.306 20.802
Table 2: Charges and Product Ratios as a
Function of Solvent for Comparative Examples
4 to 5.
Example: 4 ~ 5
solvent: toluene TBT
Mass Charged
(g)
1,5 cyclo- 1208.6 1208.7
octadiene
solvent 150.8 150.4
free radical 10.2 Vazo 64 18.4 Vazo 67
initiator in
220g solvent
Product Data
(A+B)/(C+D) 8.690 12.210
