CA2169957A1 - Production of difluoromethane - Google Patents
Production of difluoromethaneInfo
- Publication number
- CA2169957A1 CA2169957A1 CA002169957A CA2169957A CA2169957A1 CA 2169957 A1 CA2169957 A1 CA 2169957A1 CA 002169957 A CA002169957 A CA 002169957A CA 2169957 A CA2169957 A CA 2169957A CA 2169957 A1 CA2169957 A1 CA 2169957A1
- Authority
- CA
- Canada
- Prior art keywords
- formaldehyde
- difluoromethane
- hydrogen fluoride
- dehydrating agent
- production
- 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
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C17/00—Preparation of halogenated hydrocarbons
- C07C17/093—Preparation of halogenated hydrocarbons by replacement by halogens
- C07C17/18—Preparation of halogenated hydrocarbons by replacement by halogens of oxygen atoms of carbonyl groups
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Catalysts (AREA)
- Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)
Abstract
A process for the production of difluoromethane which comprises contacting formaldehyde with hydrogen fluoride in the presence of a catalyst and a chemical dehydrating agent at a temperature below 150.degree.C. Preferably BF3 is employed as both catalyst and dehydrating agent.
Description
~1 69957 ~ W09S/0662S PCT/GB94/01~8 PRODUCTION OF DIFLUOROMETHANE.
This invention relates to a process for the production of difluoromethane from formaldehyde and hydrogen fluoride.
Several methods for the production of difluoromethane are known but many of these methods involve the use of chlorine-containing starting materials, for example chlorodifluoromethane and dichloromethane, and the production of chlorine-containing by-products, for example chlorofluoromethane and fluorodichloromethane.
A chlorine-free process for the production of difluoromethane is also known. In US 3,377,394, there is disclosed a process for the production of difluoromethane and methyl fluoride by contacting formaldehyde with hydrogen fluoride at an elevated temperature in the range from about 100C to about 650C in the presence of a fluorine-containing inorganic acid, a metal fluoride, a metal oxide or a metal chromite. However, the highest yield of difluoromethane reported from this reaction is 4.2Z, the major product being methyl fluoride.
Recently, a process for the production of difluoromethane has been disclosed in published European Patent Application No. 0 518 506 in which bis(fluoromethyl)ether is heated in the vapour phase to elevated temperature. It is also disclosed in this document that bis(fluoromethyl)ether may itself be produced by contacting formaldehyde with hydrogen fluoride and separating the bis(fluoromethyl)ether from the by-product water produced, thus providing a two step process for the production of difluoromethane in which formaldehyde and hydrogen fluoride are contacted to produce bistfluoromethyl)ether and water, the bis(fluoromethyl)ether is separated from unreacted starting material and by-product water and the SUBSTITUTE StlEET (RULE 26) WO9S/0662S 2 1 6 9 q 5 7 PCT/GB94/01848 bis(fluoromethyl)ether is then heated to elevated temperature in the vapour phase.
According to the present invention there is provided a process for the production of difluoromethane which comprises contacting formaldehyde with hydrogen fluoride in the presence of a catalyst and a chemical dehydrating agent at a temperature below 150C. The catalyst and the chemical dehydrating agent may be the same or different chemical compounds. In a preferred embodiment described hereafter, the catalyst and chemical dehydrating agent are the same chemical compound.
A substantial benefit of the process of the invention resides in effecting the process in a single vessel to which formaldehyde, hydrogen fluoride, the catalyst and the dehydrating agent are charged, and from which a product stream comprising difluoromethane is withdrawn. Significantly higher yields of difluoromethane are achieved than have previously been achieved from the one step process as disclosed in US 3,377,394. The process may be operated so that, based upon the amount of formaldehyde charged to the ve~sel, difluoromethane is produced with a yield of at least 30Z. Yields of difluoromethane greater than 40~ with difluoromethane selectivities greater than 80~ have been achieved in practice.
The process is preferably effected in the liquid phase under conditions whereby the volatile difluoromethane product distills from the reaction medium. In the liquid phase process, formaldehyde is in solution in liquid hydrogen fluoride.
The formaldehyde may be provided in any of its 3~ known forms, for e~ample in one of its polymeric SUBSTITUTE SHEET (RULE 26) WO9S/06625 2 1 ~ ~ 9 5 7 PCT/GB94/01848 forms, paraformaldehyde or trioxane, or in its monomeric form which may be provided, for example, from a process stream in which it has been freshly made, for example by oxidation of methanol .
S Accordingly, whenever used herein, the term ~formaldehyde" is to be understood as including not only the monomer but also the various polymeric forms and also formaldehyde in the form of aqueous solutions, commonly known as formalin. In general, a polymeric form of formaldehyde such as paraformaldehyde or trioxane is preferred. Where an aqueous solution of formaldehyde is employed, it is preferably as concentrated as possible.
The molar ratio of formaldehyde to hydrogen fluoride may vary considerably, for example in the range about l:0.5 to l:50 but in general a stoichiometric excess of hydrogen fluoride is preferred. Typically, the molar ratio of formaldehyde to hydrogen fluoride will be in the range about 1:2 to about l:lO.
Any suitable catalyst may be employed in the process of the invention, such as for example the catalysts described in US 3,377,394. However, we generally prefer to employ a Lewis acid catalyst.
Particularly suitable Lewis acids for use in the process of the invention contain fluoride as the ligand. since where li~ands other than fluoride are present, in particular halides other than fluoride, e.g. chlorides, many undesirable by-products may be produced. However ligands other than fluoride, for esample halide other than fluoride, alkoxide, etc, may result in the production of hydrofluorocarbons and may be employed if desired. Preferred Lewis acids include the fluorides of Group III, IV and V
SUBST'ITUTE SHEET (RULE 26) WO9S/0662S ~ ~ qq 5 ~ PCT/GB94/01848 elements, for example AlF3, BF3, SnF4, SiF4, TiF4, NbFs and SbFs.
We particularly prefer to employ Lewis acids in which the central cation has a charge/radius (expressed in Angstroms) ratio of at least 5.0 and preferably at least 6Ø We especially prefer to employ SbFs, BF3, NbFs and/or TiF4 i~ the process of the invention. BF3 is the most preferred catalyst.
Some Lewis acids, for example NbFs and TiF4 may be generated in situ, for example by employing the corresponding halides other than fluorides, for example chlorides, or oxides and a source of fluoride, for example hydrogen fluoride. They may also be generated in situ b-y employing the metal itself and a source of fluoride, especially hydrogen fluoride.
Any suitable chemical dehydrating agent stable to hydrogen fluoride may be employed in the process of the invention although most conveniently BF3 is Z employed as the dehydrating agent. The proportion of dehydrating agent employed may be measured against whichever of formaldehyde or hydrogen fluoride is present in the smaller mole fraction. Typically a molar stoichiometric escess of hydrogen fluoride is employed and in this case the molar ratio of dehydrating agent to formaldehyde will usually be at least 0.5:1. and preferably at least 1:1, especially at least 1.5:1. Where howe~er formaldehyde is employed in molar excess over hydrogen fluoride, the amount of dehydrating agent may be measured against the amount of hydrogen fluoride present, so that usually in this case there will be a molar ratio of dehydrating agent to hydrogen fluoride of at least 0.5;1, preferably at least 1:1. Furthermore where water is introduced to the proce8s together with the SUBSTITUTE SHEET (RULE 26) WO9S1~6~ 9 q 5 7 P~11~31~'~1848 reactants, for example where an aqueous solution of formaldehyde is employed, much lsrger ~uantities of the dehydrating agent may be employed.
In a particularly preferred embodiment of the invention BF3 is employed as both the catalyst and the dehydrating agent. In this case the molar ratio of BF3 to formaldehyde will usually be at least 0.6:l and preferably at least l:l.
Preferably, formaldehyde will be contacted with hydrogen fluoride and the catalyst/dehydrating agent then added to the mixture.
The process is effected under conditions of temperature and pressure such that the hydrogen fluoride is in the liquid phase and preferably the volatile difluoromethane product distills as a vapour from the vessel in which the reaction is effected.
We have found that temperatures below 150C, preferably below 120C and more preferably below 100C tend to favour the selective production of difluoromethane. Preferably the temperature is in the~
range from about 0C to about 120C, more p`referably in the range from about Z0C to about 100C and especially in the range from about 20C to about 80C.
The process may be conducted at atmospheric, subatmospheric or superatmospheric pressure although superatmospheric pressures, say up to 40 bar are typically employed. Where the reaction is effected in pressure equipment, for esample an autoclave, autogenous pressure is conveniently employed.
The reaction may be conducted in suitable pressure equipment such as an autoclave or in a liquid phase reaction vessel.
The process may be operated as a batch process but is preferably operated as a continuous process in SUBSTITUTE SHEET tRULE 26) 9 ~ 1 --which formaldehyde, hydrogen fluoride and the catalystldehydrating agent are continuously fed to the reaction vessel and the volatile products are continuously withdrawn from the vessel.
The dehydrating agent/water complex by-product of the process may be drained from the vessel and the dehydrating agent may be separated from the water and recycled. Thus for~example, where the dehydrating~
agent is- BF3, the BF3 may be recovered from the BF3/water complex as is described, for example, in US
Patent 3,329,586.
Difluoromethane may be separated from other volatile products of the reaction by conventional techniques, for example distillation.
The invention is illustrated but not limited by the following e~amples.
EXA~PLE 1.
0.09 mole of trio~ane (0.27 mole of formaldehyde), 0.99 mole of hydrogen fluoride and 0.41 mole of BF3 were charged to a 70ml Hastelloy autoclave at room temperature. The autoclave was sealed and heated to 30C for 16 hours. The maximum pre~sure observed over this period was 38 bar. After 16 hours, the volatile products were distilled from the autoclave and analysed by Gas Chromatography. The volatile products comprised 86.9Z difluoromethane and 5.2Z methyl fluoride. The conversion of formaldehyde was 73.7Z, and the yield of difluoromethane, based on the formaldehyde converted, was 47.4Z.
SUBSTITUTE SHEFr (RULE 26) wo 9~ 2 t ~i ~ 5 ~ PCT/GB94/01848 EXAMPLE 2.
.
The procedure of example 1 was repeated except that 0.06 mole of trioxane (0.18 mole of formaldehyde), 0.82 mole of hydrogen fluoride and 0.21 mole of BF3 were charged to the autoclave and the autoclave was heated to 47C. The maximum pressure obser~ed was 25 bar. The volatile products comprised 81.02 difluoromethane and 16.7Z methyl fluoride. The conversion of formaldehyde was 48.52, and the yield of difluoromethane, based on the formaldehyde converted, was 33.12.
EXAMPLE 3.
The procedure of example 1 was repeated except that 0.27 moles of paraformaldehyde, 1.11 mole of hydrogen fluoride and 0.44 moles of BF3 were cha~ged to the autoclave and the autoclave was heated to 32C. The volatile products comprised 85.82 difluoromethane and the yield of difluoromethane, based on the formaldehyde converted, was 23.52.
SUBSTITUTE SHEET (RULE 26)
This invention relates to a process for the production of difluoromethane from formaldehyde and hydrogen fluoride.
Several methods for the production of difluoromethane are known but many of these methods involve the use of chlorine-containing starting materials, for example chlorodifluoromethane and dichloromethane, and the production of chlorine-containing by-products, for example chlorofluoromethane and fluorodichloromethane.
A chlorine-free process for the production of difluoromethane is also known. In US 3,377,394, there is disclosed a process for the production of difluoromethane and methyl fluoride by contacting formaldehyde with hydrogen fluoride at an elevated temperature in the range from about 100C to about 650C in the presence of a fluorine-containing inorganic acid, a metal fluoride, a metal oxide or a metal chromite. However, the highest yield of difluoromethane reported from this reaction is 4.2Z, the major product being methyl fluoride.
Recently, a process for the production of difluoromethane has been disclosed in published European Patent Application No. 0 518 506 in which bis(fluoromethyl)ether is heated in the vapour phase to elevated temperature. It is also disclosed in this document that bis(fluoromethyl)ether may itself be produced by contacting formaldehyde with hydrogen fluoride and separating the bis(fluoromethyl)ether from the by-product water produced, thus providing a two step process for the production of difluoromethane in which formaldehyde and hydrogen fluoride are contacted to produce bistfluoromethyl)ether and water, the bis(fluoromethyl)ether is separated from unreacted starting material and by-product water and the SUBSTITUTE StlEET (RULE 26) WO9S/0662S 2 1 6 9 q 5 7 PCT/GB94/01848 bis(fluoromethyl)ether is then heated to elevated temperature in the vapour phase.
According to the present invention there is provided a process for the production of difluoromethane which comprises contacting formaldehyde with hydrogen fluoride in the presence of a catalyst and a chemical dehydrating agent at a temperature below 150C. The catalyst and the chemical dehydrating agent may be the same or different chemical compounds. In a preferred embodiment described hereafter, the catalyst and chemical dehydrating agent are the same chemical compound.
A substantial benefit of the process of the invention resides in effecting the process in a single vessel to which formaldehyde, hydrogen fluoride, the catalyst and the dehydrating agent are charged, and from which a product stream comprising difluoromethane is withdrawn. Significantly higher yields of difluoromethane are achieved than have previously been achieved from the one step process as disclosed in US 3,377,394. The process may be operated so that, based upon the amount of formaldehyde charged to the ve~sel, difluoromethane is produced with a yield of at least 30Z. Yields of difluoromethane greater than 40~ with difluoromethane selectivities greater than 80~ have been achieved in practice.
The process is preferably effected in the liquid phase under conditions whereby the volatile difluoromethane product distills from the reaction medium. In the liquid phase process, formaldehyde is in solution in liquid hydrogen fluoride.
The formaldehyde may be provided in any of its 3~ known forms, for e~ample in one of its polymeric SUBSTITUTE SHEET (RULE 26) WO9S/06625 2 1 ~ ~ 9 5 7 PCT/GB94/01848 forms, paraformaldehyde or trioxane, or in its monomeric form which may be provided, for example, from a process stream in which it has been freshly made, for example by oxidation of methanol .
S Accordingly, whenever used herein, the term ~formaldehyde" is to be understood as including not only the monomer but also the various polymeric forms and also formaldehyde in the form of aqueous solutions, commonly known as formalin. In general, a polymeric form of formaldehyde such as paraformaldehyde or trioxane is preferred. Where an aqueous solution of formaldehyde is employed, it is preferably as concentrated as possible.
The molar ratio of formaldehyde to hydrogen fluoride may vary considerably, for example in the range about l:0.5 to l:50 but in general a stoichiometric excess of hydrogen fluoride is preferred. Typically, the molar ratio of formaldehyde to hydrogen fluoride will be in the range about 1:2 to about l:lO.
Any suitable catalyst may be employed in the process of the invention, such as for example the catalysts described in US 3,377,394. However, we generally prefer to employ a Lewis acid catalyst.
Particularly suitable Lewis acids for use in the process of the invention contain fluoride as the ligand. since where li~ands other than fluoride are present, in particular halides other than fluoride, e.g. chlorides, many undesirable by-products may be produced. However ligands other than fluoride, for esample halide other than fluoride, alkoxide, etc, may result in the production of hydrofluorocarbons and may be employed if desired. Preferred Lewis acids include the fluorides of Group III, IV and V
SUBST'ITUTE SHEET (RULE 26) WO9S/0662S ~ ~ qq 5 ~ PCT/GB94/01848 elements, for example AlF3, BF3, SnF4, SiF4, TiF4, NbFs and SbFs.
We particularly prefer to employ Lewis acids in which the central cation has a charge/radius (expressed in Angstroms) ratio of at least 5.0 and preferably at least 6Ø We especially prefer to employ SbFs, BF3, NbFs and/or TiF4 i~ the process of the invention. BF3 is the most preferred catalyst.
Some Lewis acids, for example NbFs and TiF4 may be generated in situ, for example by employing the corresponding halides other than fluorides, for example chlorides, or oxides and a source of fluoride, for example hydrogen fluoride. They may also be generated in situ b-y employing the metal itself and a source of fluoride, especially hydrogen fluoride.
Any suitable chemical dehydrating agent stable to hydrogen fluoride may be employed in the process of the invention although most conveniently BF3 is Z employed as the dehydrating agent. The proportion of dehydrating agent employed may be measured against whichever of formaldehyde or hydrogen fluoride is present in the smaller mole fraction. Typically a molar stoichiometric escess of hydrogen fluoride is employed and in this case the molar ratio of dehydrating agent to formaldehyde will usually be at least 0.5:1. and preferably at least 1:1, especially at least 1.5:1. Where howe~er formaldehyde is employed in molar excess over hydrogen fluoride, the amount of dehydrating agent may be measured against the amount of hydrogen fluoride present, so that usually in this case there will be a molar ratio of dehydrating agent to hydrogen fluoride of at least 0.5;1, preferably at least 1:1. Furthermore where water is introduced to the proce8s together with the SUBSTITUTE SHEET (RULE 26) WO9S1~6~ 9 q 5 7 P~11~31~'~1848 reactants, for example where an aqueous solution of formaldehyde is employed, much lsrger ~uantities of the dehydrating agent may be employed.
In a particularly preferred embodiment of the invention BF3 is employed as both the catalyst and the dehydrating agent. In this case the molar ratio of BF3 to formaldehyde will usually be at least 0.6:l and preferably at least l:l.
Preferably, formaldehyde will be contacted with hydrogen fluoride and the catalyst/dehydrating agent then added to the mixture.
The process is effected under conditions of temperature and pressure such that the hydrogen fluoride is in the liquid phase and preferably the volatile difluoromethane product distills as a vapour from the vessel in which the reaction is effected.
We have found that temperatures below 150C, preferably below 120C and more preferably below 100C tend to favour the selective production of difluoromethane. Preferably the temperature is in the~
range from about 0C to about 120C, more p`referably in the range from about Z0C to about 100C and especially in the range from about 20C to about 80C.
The process may be conducted at atmospheric, subatmospheric or superatmospheric pressure although superatmospheric pressures, say up to 40 bar are typically employed. Where the reaction is effected in pressure equipment, for esample an autoclave, autogenous pressure is conveniently employed.
The reaction may be conducted in suitable pressure equipment such as an autoclave or in a liquid phase reaction vessel.
The process may be operated as a batch process but is preferably operated as a continuous process in SUBSTITUTE SHEET tRULE 26) 9 ~ 1 --which formaldehyde, hydrogen fluoride and the catalystldehydrating agent are continuously fed to the reaction vessel and the volatile products are continuously withdrawn from the vessel.
The dehydrating agent/water complex by-product of the process may be drained from the vessel and the dehydrating agent may be separated from the water and recycled. Thus for~example, where the dehydrating~
agent is- BF3, the BF3 may be recovered from the BF3/water complex as is described, for example, in US
Patent 3,329,586.
Difluoromethane may be separated from other volatile products of the reaction by conventional techniques, for example distillation.
The invention is illustrated but not limited by the following e~amples.
EXA~PLE 1.
0.09 mole of trio~ane (0.27 mole of formaldehyde), 0.99 mole of hydrogen fluoride and 0.41 mole of BF3 were charged to a 70ml Hastelloy autoclave at room temperature. The autoclave was sealed and heated to 30C for 16 hours. The maximum pre~sure observed over this period was 38 bar. After 16 hours, the volatile products were distilled from the autoclave and analysed by Gas Chromatography. The volatile products comprised 86.9Z difluoromethane and 5.2Z methyl fluoride. The conversion of formaldehyde was 73.7Z, and the yield of difluoromethane, based on the formaldehyde converted, was 47.4Z.
SUBSTITUTE SHEFr (RULE 26) wo 9~ 2 t ~i ~ 5 ~ PCT/GB94/01848 EXAMPLE 2.
.
The procedure of example 1 was repeated except that 0.06 mole of trioxane (0.18 mole of formaldehyde), 0.82 mole of hydrogen fluoride and 0.21 mole of BF3 were charged to the autoclave and the autoclave was heated to 47C. The maximum pressure obser~ed was 25 bar. The volatile products comprised 81.02 difluoromethane and 16.7Z methyl fluoride. The conversion of formaldehyde was 48.52, and the yield of difluoromethane, based on the formaldehyde converted, was 33.12.
EXAMPLE 3.
The procedure of example 1 was repeated except that 0.27 moles of paraformaldehyde, 1.11 mole of hydrogen fluoride and 0.44 moles of BF3 were cha~ged to the autoclave and the autoclave was heated to 32C. The volatile products comprised 85.82 difluoromethane and the yield of difluoromethane, based on the formaldehyde converted, was 23.52.
SUBSTITUTE SHEET (RULE 26)
Claims (6)
1. A process for the production of difluoromethane which comprises contacting formaldehyde with hydrogen fluoride in the presence of a catalyst and a chemical dehydrating agent at a temperature below 150°C.
2. A process as claimed in claim 1 in which the temperature is below 120°C.
3. A process as claimed in claim 1 in which the temperature is below 100°C.
4. A process as claimed in any one of claims 1 to 3 in which the catalyst and the chemical dehydrating agent are BF3.
5. A process as claimed in claim 4 in which the molar proportion of BF3 to formaldehyde is at least 0.6:1.
6. A process as claimed in claim 4 in which the molar proportion of BF3 to formaldehyde is at least 1:1.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9318277.2 | 1993-09-03 | ||
| GB939318277A GB9318277D0 (en) | 1993-09-03 | 1993-09-03 | Production of difluoromethane |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2169957A1 true CA2169957A1 (en) | 1995-03-09 |
Family
ID=10741446
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002169957A Abandoned CA2169957A1 (en) | 1993-09-03 | 1994-08-24 | Production of difluoromethane |
Country Status (7)
| Country | Link |
|---|---|
| EP (1) | EP0716644A1 (en) |
| JP (1) | JPH09502179A (en) |
| AU (1) | AU7465694A (en) |
| CA (1) | CA2169957A1 (en) |
| GB (2) | GB9318277D0 (en) |
| WO (1) | WO1995006625A1 (en) |
| ZA (1) | ZA946619B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2554982A1 (en) | 2003-09-26 | 2005-04-07 | Japan Tobacco Inc. | Method of inhibiting remnant lipoprotein production |
| FR2912403B1 (en) * | 2007-02-13 | 2012-06-22 | Arkema France | PROCESS FOR THE PRODUCTION OF METHYLENE CHLORIDE |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3377394A (en) * | 1966-07-15 | 1968-04-09 | Olin Mathieson | Methyl fluoride and methylene fluoride process |
-
1993
- 1993-09-03 GB GB939318277A patent/GB9318277D0/en active Pending
-
1994
- 1994-08-23 GB GB9416962A patent/GB9416962D0/en active Pending
- 1994-08-24 CA CA002169957A patent/CA2169957A1/en not_active Abandoned
- 1994-08-24 WO PCT/GB1994/001848 patent/WO1995006625A1/en not_active Application Discontinuation
- 1994-08-24 AU AU74656/94A patent/AU7465694A/en not_active Abandoned
- 1994-08-24 JP JP7507992A patent/JPH09502179A/en active Pending
- 1994-08-24 EP EP94924362A patent/EP0716644A1/en not_active Withdrawn
- 1994-08-30 ZA ZA946619A patent/ZA946619B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| EP0716644A1 (en) | 1996-06-19 |
| GB9416962D0 (en) | 1994-10-12 |
| GB9318277D0 (en) | 1993-10-20 |
| WO1995006625A1 (en) | 1995-03-09 |
| JPH09502179A (en) | 1997-03-04 |
| AU7465694A (en) | 1995-03-22 |
| ZA946619B (en) | 1995-03-06 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |