GB2089801A - Electro chemical dechlorination of chloro-trifluoromethyl-pyridines - Google Patents
Electro chemical dechlorination of chloro-trifluoromethyl-pyridines Download PDFInfo
- Publication number
- GB2089801A GB2089801A GB8138539A GB8138539A GB2089801A GB 2089801 A GB2089801 A GB 2089801A GB 8138539 A GB8138539 A GB 8138539A GB 8138539 A GB8138539 A GB 8138539A GB 2089801 A GB2089801 A GB 2089801A
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- GB
- United Kingdom
- Prior art keywords
- trifluoromethylpyridine
- chloro
- dichloro
- minus
- volts
- 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.)
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07D—HETEROCYCLIC COMPOUNDS
- C07D213/00—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members
- C07D213/02—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members
- C07D213/04—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen or carbon atoms directly attached to the ring nitrogen atom
- C07D213/60—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen or carbon atoms directly attached to the ring nitrogen atom with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
- C07D213/61—Halogen atoms or nitro radicals
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07D—HETEROCYCLIC COMPOUNDS
- C07D213/00—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members
- C07D213/02—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members
- C07D213/04—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen or carbon atoms directly attached to the ring nitrogen atom
- C07D213/24—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen or carbon atoms directly attached to the ring nitrogen atom with substituted hydrocarbon radicals attached to ring carbon atoms
- C07D213/26—Radicals substituted by halogen atoms or nitro radicals
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B3/00—Electrolytic production of organic compounds
- C25B3/20—Processes
- C25B3/25—Reduction
Abstract
Preparation of 3-trifluoromethyl- pyridine or 2-chloro-5-trifluoromethyl- pyridine is effected by electrochemical dechlorination of an appropriate chloro-trfluoromethyl-pyridine or dichloro-trifluoromethyl-pyridine.
Description
SPECIFICATION
Electrochemical dechlorination
The present invention relates to an electrochemical process and more particularly to an electrochemical process for the selective dechlorination of chlorinated pyridine derivatives.
2-Chlorn-5-trifluornmethylpy7idine and 3-tri-fluoromethylpyridine are intermediates for the preparation of herbicides. In United Kingdom Application GB 2 045 245 A there is described a process wherein 3-picoline is reacted with chlorine and hydrogen fluoride in the vapour phase; this process can be operated to yield 2-chloro-5-trifluoromethylpyridine as the main product, accompanied by 2-chloro-3-trifluoro-methylpyridine and 2, 6-dichloro-3-trifluoromethyl-pyrid i ne as by-products. It is described that the said by-products may be dechlorinated by a catalytic hydrogenation process to yield 3-tri-fluoromethylpyridine, which may then be recycled to the stage in which 2-chloro-5-trifluoromethyl-pyridine is produced.In the catalytic hydrogenation, however, the yield of the desired 3-tri-fluoromethylpyridine is rather low and defluorination of the side-chain occurs to some extent, leading to a proportion of 3-difluoromethylpyridine in the product.
We have now found that dechlorination or selective partial dechlorination of chloro-ss-tri- fluoromethylpyridines may be carried out electrochemically. When the starting matrial is 2 chloro-3-trifluoromethylpyridine, 2-chloro-5-trifluoromethylpyridine or 2,6-dichloro-3-trifluoromethylpyridine complete dechlorination may be effected to yield 3-trifluoromethylpyridine.Furthermore we have found that 2,6-dichloro-3-trifluoromethylpyridine may be selectively dechlorinated to yield 2-chloro-5-trifluoromethylpyridine, which may be separated as such from the dechlorination products; this makes it possible to avoid the wasteful process of complete dechlorination of 2,6-dichloro-3-trifluoro-methylpyridine to 3-trifluoromethylpyridine, which would then have to be converted into the desired 2-chloro-S4rifluoromethyl pyridine.
Thus according to the present invention there is provided a process for the selective dehalogenation of a chloro-ss-trifluoromethylpyridine, characterised in that: (i) 2-chloro-5-trifluoromethylpyridine is produced by electrochemical partial dechlorination of 2,6-dichloro-3-trifluoromethylpyridine and/or (ii) 3-trifluoromethylpyridine is produced by electrochemical dechlorination of 2-chloro-3trifluoromethylpyridine, 2-chloro-5-trifluoromethylpyridine or 2, 6-dichloro-3-trifluoromethylpyridine.
The half-wave potential for the selective partial dechlorination of 2,6-dichloro-3-trifluoromethylpyridine to yield 2-chloro-5-trifluoromethylpyridine is minus 1.7 volts. (All potentials specified herein are with reference to the standard Ag/AgCI electrode).
The half-wave potential for the production of 3-trifluoromethylpyridine from 2-chloro-3trifluoromethylpyridine (or, if desired, from 2-chloro-5-trifluoromethylpyridine) is minus 1.8 volts.
In general, the process of the present invention is carried out at a cathode potential at least as negative as minus 1.6 volts. If it is desired to produce 2-chloro-5-trifluoromethylpyridine from 2,6-dichloro-3 trifluoromethylpyridine the electrochemical process is preferably carried out at a cathode potential which is at least as negative as minus 1.7 volts but less negative than the potential of about minus 1.8 volts at which the further dechlorination to 3-trifluoro-methylpyridine would occur. At a potential between minus 1.6 and minus 1.7 the derived reaction will proceed, but less efficiently.
If it is desired to produce 3-trifluoromethylpyridine from 2-chloro-3-trifluoromethylpyridine from 2-chloro-5-trifluoromethylpyridine or from 2, 6-dichloro-3-trifluoromethylpyridine the electrochemical process is preferably carried out at a cathode potential at least as negative as minus 1.8 volts but less negative than the potential of about minus 2.1 volts at which 3 trifluoromethylpyridine is itself reduced to 3-methylpyridine.
I the dechlorination of a mixture of starting compounds such as a mixture of by-products obtained in the reaction between 3-picoline, chlorine and hydrogen fluoride (as described in GB 2 045 245 A) a variety of procedures are possible.
Thus starting with a mixture in which the main components are 2,6-dichloro-3-trifluoromethylpyridine and 2-chloro-3-trifluoromethylpyridine the electrochemical process may be carried out at sucha potential that both starting materials are converted into 3-trifluoromethylpyridine; this may then be separated by conventional methods (for example distillation) and then chlorinated to yield 2-chloro-5-trifluoromethylpyridine. Such chlorination may be carried out separately (as described in European Publication 0 013 474) or may be combined with the reaction between 3-picoline, chlorine and hydrogen fluoride (as described in GB 2 045 245A).
Alternatively, the elctrochemical process may be carried out in two stages as follows: (i) In the first stage the 2,6-dichloro-5-trifluoromethylpyridine is converted into 2-chloro-5trifluoromethylpyridine at the appropriate potential, thereby producing a mixture of 2-chloro-5trifluoromethylpyridine and 2-chloro-3-trifluoromethylpyridine. The 2-chloro-5-trifluoromethylpyri- dine may be separated from this mixture by conventional methods (for example by distillation).
(ii) In the second stage the residual 2-chloro-3-trifluoromethylpyridine is converted into 3trifluoromethylpyridine at the appropriate potential (more negative than that employed in the first stage). The 3-trifluoromethylpyridine may then be separated by conventional methods and used in the production of 2-chloro-5-trifluoromethylpyridine as previously described herein.
Another way of treating a mixture of 2,6-dichloro-3-trifluoromethylpyridine and 2-chloro-3trifluoromethylpyridine is first to separate the relatively volatile 2-chloro-3-trifluoromethylpyridine by distillation and then to carry out the electrochemical selective partial dechlorination of the residual 2,6-dichlora-3-trifluoromethylpyridine to yield the desired 2-chloro-5-trifluoromethylpyridine.
Another procedure is to carry out the vapour-phase reaction of 3-picoline with chlorine and hydrogen fluoride under such conditions, and employing such relative proportions of the reactants, that the proportion of 2,6-dichloro-3-trifluoromethylpyridine in the reaction products is maximised (for example as described in GB 2 045 245A); the 2,6-dichloro-3-trifluoromethylpyridine may then be separated from the other products and subjected to selective partial dechlorination to yield 2-chloro-5-trifluoromethylpyridine.
The electrochemical process may be carried out using techniques well known in the art, using either a cell divided into anode and cathode compartments or an undivided cell. The cathode may be, for example, a lead cathode or a mercury cathode. The material to be dechlorinated may be dissolved in a wide variety of organic solvents which are inert towards electrochemical reduction, the solvent containing a carrier electrolyte which is similarly inert towards electrochemical reduction.
Suitable solvents include dipolar aprotic solvents, for example dimethylformamide, acetonitrile, N-methylpyrrolidone, dimethyl sulphoxide, sulpholane and propylene carbonate. Electrolysis may also be carried out in a two-phase system of a dipolar aprotic solvent and water, for example a water/propylene carbonate emulsion. Suitable carrier electrolytes include tetralkylammonium salts (for example tetrabutylammonium tetrafluoroborate) and sodium and lithium perchlorates.
In the following Examples 1 to 3 the electrochemical process was carried out using a Istandard H-cell, with a mercury cathode, a platinum anode and a glass-fibre paper cell-compartment separator. The solvent used was dimethylformamide and the background electrolyte was 0.1 molar tertabutylammonium tetrafluoroborate. Electrolysis was carried out galvanostatically at a cell current of 50 mA which ensured that electrolysis was taking place only on the first reduction wave of the substrate (i.e. at the potentials hereinbefore described for the removal of a single chlorine atom from each compound).
In all cases analysis of the products was carried out using gas chromatography.
EXAMPLE 1 (Electrolysis of 2-chloro-5-trifluoromethylpyridine) The solution initially contained 2 X 10-3 moles of 2-chloro-5-trifluoromethylpyridine.
Samples were taken after successive periods of electrolysis and analysed for 3-trifluoromethylpyridine produced and for unconverted 2-chloro-5-trifluoromethylpyridine with the following results.
Total Moles 3-trifluoromethylpyrid ine coulombs produced per hundred moles initial passed 2-chloro-5-trifluoromethylpyridine 50 12 100 22 200 42 320 70
At the end of this period the 2-chloro-5-trifluoromethylpyridine had been substantially completely consumed.
EXAMPLE 2 (Electrolysis of 2-chloro-3-trifluoro-methylpyridine)
The procedure was similar to the described in Example 1. Samples were analysed for 3trifluoromethylpyridine produced and for unconverted 2-chloro-3-trifluoromethylpyridine.
Total Moles 3-trifluoromethylpyridine coulombs produced per hundred moles initial passed 2-chloro-3-trifluoromethylpyridine
50 13 136 41 200 62 250 78 272 80
At the end of this period the 2-chloro-3-trifluoromethylpyridine was substantially completely consumed.
EXAMPLE 3 (Two-stage electrolysis of 2,6-dichloro-5-trifluoromethylpyridine)
The procedure was similar to that described in Example 1. Samples were analysed for: (a) 2-chloro-5-trifluoromethylpyridine produced in the first dechlorination stage, (b) 3-trifluoromethylpyridine produced by further dechlorination of 2-chloro-5-trifluoromethylpyridine in the second stage and (c) unconverted 2, 6-dichlorn-5-trifluoromethyl-pyridine.
Total moles produced per hundred moles coulombs initial 2,6-dichloro-5-trifluoropassed methylpyridine
2-chloro- 3-trifluoro
5-trifluoromethyl- methylpyridine
pyridine
50 13 0 110 28 0 160 44 0 300 30 9 450 3 34 500 1 49
After 300 coulombs had been passed no unconverted 2,6-dichloro-5-trifluoromethylpyridine could be detected.
It will be seen that the selective dechlorination to yield 2-chloro-5-trifluoromethylpyridine could readily be optimised by carrying out a similar procedure but stopping the electrolysis after about 1 60 coulombs had been passed.
EXAMPLE 4
The procedure of Example 2 was followed except that the electrolysis of 2-chloro-3trifluoromethyl-pyridine was carried out potentiostatically at a cathode potential of minus 1.72 volts (anode current 50 mA).
The yield of 3-trifluoromethylpyridine was 80% based on 2-chloro-3-trifluoromethylpyridine consumed.
EXAMPLE 5
2,6-dichloro-5-trifluoromethylpyridine was subjected to electrolysis is an undivided cell using a mercury cathode and a platinum anode. The cathode potential was minus 1.67 volts (anode current 1 80 mA).
The yield of 2-chloro-5-trifluoromethylpyridine was 50% based on 2,6-dichloro-5-trifluoromethylpyridine consumed.
Claims (5)
1. A process for the selective dehalogenation of a chloro-ss-trifluoromethylpyridine, characterised in that: (i) 2-chloro-5-trifluoromethylpyridine is proudced by electrochemical partial dechlorination of 2.6-dichloro-3-trifluoromethylpyridine and/or (ii) 3-trifluoromethylpyridine is produced by electrochemical dechlorination of 2-chloro-3 trifluoromethylpyrid ine or 2,6-dichloro-3-trifluoromethylpyridine.
2. A process according to Claim 1, characterised in that the electrochemical process is carried out at a cathode potential at least as negative as minus 1.6 volts with reference to the standard silver chloride electrode.
3. A process according to Claim 2, characterised in that 2-chloro-5-trifluoromethylpyridine is produced from 2,6-dichloro-3-trifluoromethyl pyridine using a cathode potential at least as negative as minus 1.7 volts but less negative than minus 1.8 volts.
4. A process according to Claim 2, characterised in that 3-trifluoromethylpyridine is produced from 2-chloro-3-trifluoromethylpyridine, 2-chloro-5-trifluoromethylpyridine or 2,6-dichloro-3-trifluoromethylpyridine using a cathode potential at least as negative as minus 1.8 volts but less negative than minus 2.1 volts. +
5. A process according to any of the preceding claims, characterised in that the reaction medium comprises a dipolar aprotic solvent.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8138539A GB2089801A (en) | 1980-12-22 | 1981-12-22 | Electro chemical dechlorination of chloro-trifluoromethyl-pyridines |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8040956 | 1980-12-22 | ||
| GB8138539A GB2089801A (en) | 1980-12-22 | 1981-12-22 | Electro chemical dechlorination of chloro-trifluoromethyl-pyridines |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2089801A true GB2089801A (en) | 1982-06-30 |
Family
ID=26277933
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8138539A Withdrawn GB2089801A (en) | 1980-12-22 | 1981-12-22 | Electro chemical dechlorination of chloro-trifluoromethyl-pyridines |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2089801A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0226275A1 (en) * | 1985-09-23 | 1987-06-24 | Tracer Technologies, Inc. | Electrochemical dehalogenation of organic compounds |
| US5102510A (en) * | 1990-08-23 | 1992-04-07 | Ensr Corporation | Process for electrochemical dehalogenation of organic contaminants |
-
1981
- 1981-12-22 GB GB8138539A patent/GB2089801A/en not_active Withdrawn
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0226275A1 (en) * | 1985-09-23 | 1987-06-24 | Tracer Technologies, Inc. | Electrochemical dehalogenation of organic compounds |
| US5102510A (en) * | 1990-08-23 | 1992-04-07 | Ensr Corporation | Process for electrochemical dehalogenation of organic contaminants |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |