CA2291503A1 - Synthesis of organic phosphines - Google Patents
Synthesis of organic phosphines Download PDFInfo
- Publication number
- CA2291503A1 CA2291503A1 CA 2291503 CA2291503A CA2291503A1 CA 2291503 A1 CA2291503 A1 CA 2291503A1 CA 2291503 CA2291503 CA 2291503 CA 2291503 A CA2291503 A CA 2291503A CA 2291503 A1 CA2291503 A1 CA 2291503A1
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- CA
- Canada
- Prior art keywords
- phosphine
- cyclooctadiene
- reaction
- solvent
- radical initiator
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
- C07F9/00—Compounds containing elements of Groups 5 or 15 of the Periodic System
- C07F9/02—Phosphorus compounds
- C07F9/28—Phosphorus compounds with one or more P—C bonds
- C07F9/50—Organo-phosphines
- C07F9/505—Preparation; Separation; Purification; Stabilisation
- C07F9/5059—Preparation; Separation; Purification; Stabilisation by addition of phosphorus compounds to alkenes or alkynes
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07F—ACYCLIC, CARBOCYCLIC OR HETEROCYCLIC COMPOUNDS CONTAINING ELEMENTS OTHER THAN CARBON, HYDROGEN, HALOGEN, OXYGEN, NITROGEN, SULFUR, SELENIUM OR TELLURIUM
- C07F9/00—Compounds containing elements of Groups 5 or 15 of the Periodic System
- C07F9/02—Phosphorus compounds
- C07F9/547—Heterocyclic compounds, e.g. containing phosphorus as a ring hetero atom
- C07F9/6558—Heterocyclic compounds, e.g. containing phosphorus as a ring hetero atom containing at least two different or differently substituted hetero rings neither condensed among themselves nor condensed with a common carbocyclic ring or ring system
- C07F9/65586—Heterocyclic compounds, e.g. containing phosphorus as a ring hetero atom containing at least two different or differently substituted hetero rings neither condensed among themselves nor condensed with a common carbocyclic ring or ring system at least one of the hetero rings does not contain nitrogen as ring hetero atom
Abstract
9-phosphabicyclononanes are prepared by adding phosphine to a 1,5-cyclooctadiene in the presence of a free radical initiator in a polar solvent. Use of a polar solvent favours the formation of [3.3.1]- and [4.2.1]-9-phosphabicyclononanes over other secondary or tertiary phosphine products.
Description
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.
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 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 (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 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 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 (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 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
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.
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 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 (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 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 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 (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 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
Claims (5)
1. 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.
2. The process according to claim 1, wherein the polar solvent is a C1-3 alcohol.
3. The process according to claim 1, wherein the polar solvent is methanol or ethanol.
4. The process according to any one of claims 1 to 3, wherein the free radical initiator is an azo compound.
5. The process according to claim 4, wherein the azo compound is selected from the group consisting of 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), and 1,1'-azobis(cyclohexanecarbonitrile).
Priority Applications (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2291503 CA2291503A1 (en) | 1999-12-03 | 1999-12-03 | Synthesis of organic phosphines |
| GB0212174A GB2372989B (en) | 1999-12-03 | 2000-11-28 | Synthesis of organic phosphines |
| PCT/US2000/032502 WO2001040237A1 (en) | 1999-12-03 | 2000-11-28 | Synthesis of organic phosphines |
| AU22525/01A AU2252501A (en) | 1999-12-03 | 2000-11-28 | Synthesis of organic phosphines |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2291503 CA2291503A1 (en) | 1999-12-03 | 1999-12-03 | Synthesis of organic phosphines |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2291503A1 true CA2291503A1 (en) | 2001-06-03 |
Family
ID=4164787
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2291503 Abandoned CA2291503A1 (en) | 1999-12-03 | 1999-12-03 | Synthesis of organic phosphines |
Country Status (4)
| Country | Link |
|---|---|
| AU (1) | AU2252501A (en) |
| CA (1) | CA2291503A1 (en) |
| GB (1) | GB2372989B (en) |
| WO (1) | WO2001040237A1 (en) |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2703802C3 (en) * | 1977-01-29 | 1979-07-12 | Hoechst Ag, 6000 Frankfurt | Process for the continuous production of organic phosphines |
| DE3629189A1 (en) * | 1986-08-28 | 1988-03-17 | Hoechst Ag | METHOD FOR THE PRODUCTION OF TERTIAL ALKYLPHOSPHANS |
| GB9117603D0 (en) * | 1991-08-15 | 1991-10-02 | Albright & Wilson | Organophorus compounds |
| CA2264429A1 (en) * | 1999-03-03 | 2000-09-03 | Allan James Robertson | Preparation of 9-hydrocarbyl-9-phosphabicyclononanes |
-
1999
- 1999-12-03 CA CA 2291503 patent/CA2291503A1/en not_active Abandoned
-
2000
- 2000-11-28 WO PCT/US2000/032502 patent/WO2001040237A1/en active Application Filing
- 2000-11-28 GB GB0212174A patent/GB2372989B/en not_active Expired - Fee Related
- 2000-11-28 AU AU22525/01A patent/AU2252501A/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| GB2372989A (en) | 2002-09-11 |
| WO2001040237A1 (en) | 2001-06-07 |
| GB0212174D0 (en) | 2002-07-03 |
| AU2252501A (en) | 2001-06-12 |
| GB2372989B (en) | 2004-04-28 |
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