CA2191652A1 - Process for preparing 1-bromo-3,5-difluorobenzene - Google Patents
Process for preparing 1-bromo-3,5-difluorobenzeneInfo
- Publication number
- CA2191652A1 CA2191652A1 CA002191652A CA2191652A CA2191652A1 CA 2191652 A1 CA2191652 A1 CA 2191652A1 CA 002191652 A CA002191652 A CA 002191652A CA 2191652 A CA2191652 A CA 2191652A CA 2191652 A1 CA2191652 A1 CA 2191652A1
- Authority
- CA
- Canada
- Prior art keywords
- bromo
- difluorobenzene
- difluoroaniline
- hbr
- preparing
- 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
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
The invention relates to a process for preparing 1-bromo-3,5-difluorobenzene, which comprises converting 3,5-difluoroaniline into its diazonium salt and then reacting the diazonium salt with HBr in the presence of CuBr.
Description
HOECHST AKTIENGESELLSCHAFT HOE 95/F 276 Dr. Mu/pp Description 5 A process for preparing 1-bromo-3,5-difluorobenzene The present invention relates to a process for preparing 1-bromo-3,5-difluorobenzene.
10 1-Bromo-3,5-difluorobenzene is an intermediate for preparing pharmaceutics and liquid crystals.
According to the prior art,1-bromo-3,5-difluorobenzene can be prepared by the following processes:
1. by bromination of 2,4-difluoroaniline, subsequent diazotization with NaNO2 and deamination using hypophosphorous acid in acid solution.
Employing this process, A. Roe and W.F. Little, J. Org. Chem. 20 (1955) 1577/1590 obtained 1-bromo-3,5-difluorobenzene in a yield of 60%.
L. l. Kruse et al., J. Org. Med., 29 (1986) 887/889 and J. Org. Med., 30 (1987) 486/494 obtained a total yield of 1-bromo-3,5-difluoro-enzene of 57%.
In US 5 157 169, a yield of 1-bromo-3,5-difluorobenzene of 70% is described.
The yields obtained when employing this process are low, especially in the deamination step, expensive starting materials are wasted.
The process comprises many steps.
10 1-Bromo-3,5-difluorobenzene is an intermediate for preparing pharmaceutics and liquid crystals.
According to the prior art,1-bromo-3,5-difluorobenzene can be prepared by the following processes:
1. by bromination of 2,4-difluoroaniline, subsequent diazotization with NaNO2 and deamination using hypophosphorous acid in acid solution.
Employing this process, A. Roe and W.F. Little, J. Org. Chem. 20 (1955) 1577/1590 obtained 1-bromo-3,5-difluorobenzene in a yield of 60%.
L. l. Kruse et al., J. Org. Med., 29 (1986) 887/889 and J. Org. Med., 30 (1987) 486/494 obtained a total yield of 1-bromo-3,5-difluoro-enzene of 57%.
In US 5 157 169, a yield of 1-bromo-3,5-difluorobenzene of 70% is described.
The yields obtained when employing this process are low, especially in the deamination step, expensive starting materials are wasted.
The process comprises many steps.
2. by photochemical bromination of m-difluorobenzene R. Bolton and E.S.E. Owen, J. Fluor. Chem. 46 (1990) 393/406 state that according to this process 19% of 1 -bromo-3,5-difluorobenzene are formed in addition to 10% of other bromodifluorobenzene isomers and 43% of more highly brominated difluorobenzenes. In this process, the formation of 1-bromo-3,5-difluorobenzene is of poor selectivity.
1-Bromo-3,5-difluorobenzene cannot be obtained by direct bromination of m-difluorobenzene. It selectively produces 1-bromo-2,4-difluorobenzene.
1-Bromo-3,5-difluorobenzene cannot be obtained by direct bromination of m-difluorobenzene. It selectively produces 1-bromo-2,4-difluorobenzene.
- 3. by isomerization of 1-bromo-2,4-difluorobenzene In EP 63066, the isomerization of 1-bromo-2,4-difluorobenzene is carried out in the presence of alkali metal bases, preferably alkali metal amides, and macrocyclic compounds such as polyethers.
This process has a number of disadvantages. The macrocyclic compounds are of a complex structure and therefore very expensive. They are not recovered after the reaction. To work up the product, the basic reaction mixture has to be neutralized, resulting in the formation of salts. Because of the low yields of 1-bromo-3,5-difluorobenzene (about 63%) and the high costs of material, this process is of little economic value.
JP 04 182 440 (CA 117: 170951n) describes the isomerization of 1-bromo-2,4-difluorobenzene in the presence of alkali metall t-butoxides or aluminum halides. This process likewise requires an additional, salt-forming neutralization step. The yield of 1-bromo-3,5-difluorobenzene is only 41.4%.
EP 648 724 describes the isomerization of 1-bromo-2,4--difluorobenzene using acidic zeolites as catalysts. Disadvantages of this process are, on the one hand, the large amounts which have to be recycled because of the limited conversion and, on the other, the cost of continuous apparatus.
No other starting materials for the preparation of 1-bromo-3,5-difluorobenzene are described in the literature.
Therefore, there was a need for a process avoiding the disadvantages 10 described and providing an easy industrial route to 1-bromo-3,5-difluoro-benzene in high yields and with high selectivity.
-This object is achieved by a process for preparing 1-bromo-3,5-difluoro-benzene, which comprises converting 3,5-difluoroaniline into its diazonium 15 salt and then converting the diazonium salt in the presence of CuBr and HBr into 1-bromo-3,5-difluorobenzene.
3,5-Difluoroaniline is a known compound. An advantageous way for preparing 3,5-difluoroaniline is described for example in EP 562 435.
The preparation of halogenated aromatic compounds from the - -corresponding anilines is known and comprehensively described in the literature (Sandmeyer reaction). For instance, there are synthetic procedures for the diazotization of anilines and the Sandmeyer reaction of 25 the diazonium salts to the corresponding halogenated aromatic compounds, for example in Organikum, 4th edition (1964), 491/492 and 497/499, Org. Synth., Coll. Vol. 3,185-187, Houben-Weyl, Halogen compounds, Volume V/4 (1960), 438/446. According to these procedures, halogenated aromatic compounds can be prepared in high yields between 30 80 and 95% from the respective anilines.
It is all the more surprising, then, that the technical literature does not -mention the conversion of 3,5-difluoroaniiine into 1-bromo-3,5-difluoro-benzene.
On the other hand, several papers describe the preparation of 1-bromo-3,5-difluorobenzene starting from 2,4-difluoroaniline, an isomer of 3,5-difluoroaniline. 2,4-Difluoroaniline is first converted by bromination into 2-bromo-4,6-difluoroaniline, followed by diazotization with NaNO2 and deamination using hypophosphorous acid in acid solution to give 1-bromo-3,5-difluorobenzene. This pathway involves one more step than the process according to the invention. In addition, yields of the deamination using hypophosphorous acid are substantially lower than the yields for the - Sandmeyer reaction described in the literature.
Since the direct conversion of 3,5-difluoroaniline into 1-bromo-3,5-15 difluorobenzene has not been described, it is reasonable to assume that this reaction can only be carried out with difficulties and that the indirect route via 2,4-difluoroaniline, bromination, diazotization and deamination is more favorable.
20 By contract, it was now been found that, surprisingly, 1-bromo-3,5-difluorobenzene can be prepared in high yield directly from 3,5-difluoroaniline by diazotization and subsequent Sandmeyer reaction.
For the diazotization of 3,5-difluoroaniline with an equimolar amount of 25 NaNO2, a 2.5- to 3-fold excess of HBr is sufficient. It proved useful to add the acid in 48% strength and to carry out the reaction at low temperatures, most favorably at temperatures c1 0C.
NaNO2 is added as about 50% strength solution. By checking the color 30 reaction with starch-iodide paper, it is ensured that no excess nitrite is present. If necess~ry, some urea is added.
The diazonium salt formed is kept at about 10C until further processing.
Either, the entire diazonium salt is added at 0C to the CuBr/HBr, and only then heated to the boil. Or, alternatively, the initially charged CuBr/HBr mixture is heated to the boil and the cooled diazonium salt is added a little at a time, so that the whole mixture is kept at the boil.
The 1-bromo-3,5-difluorobenzene formed is distilled off together with steam. Heating is continued until no further gas is evolved. Then, to recover all the reaction products, the remaining organic product is distilled using steam.
The organic phase is separated off from the aqueous phase, neutralized with dilute alkali metal hydroxide solution, washed, dried and then redistilled to purity.
The following example illustrates the process according to the invention.
Example 1:
Diazotization:
A 500 ml four-neck flask fitted with stirrer, thermometer and dropping funnel is initially charged with 64.5 g (0.5 mol) of 3,5-difluoroaniline and 210 ml of 48% strength HBr (1.25 mol of HBr), and at <10C 34.5 g (0.5 mol) of NaNO2 in 60 ml of water are added with stirring. NaNO2 is added until free HNO2 is just detectable by color reaction with starch-iodide paper.
Sandmeyer reaction:
The reaction mixture kept at 10C is added a little at a time with stirring to aboiling mixture of 35.4 g (0.25 mol) of CuBr in 46 ml of 48% strength HBr (0.27 mol of HBr) in a 1 I four-neck flask fitted with a distillation apparatus,steam-inlet tube, dropping funnel and thermometer. Heating is continued to keep the mixture at the boil. Organic product and water begin to distill over during the addition of diazonium salt. On completion of the addition, steam 5 distillation is continued until no more organic product is collected in the receiving flask.
The phases in the receiving flask are separated, the organic phase is washed first with water, then neutralized with 5% strength NaOH and 10 subsequently washed neutral. After drying over Na2SO4 and redistillation to purity, 80 9 (0.41 mol) of 1-bromo-3,5-difluorobenzene are obtained, equivalent to a yield of 83% of theory.
This process has a number of disadvantages. The macrocyclic compounds are of a complex structure and therefore very expensive. They are not recovered after the reaction. To work up the product, the basic reaction mixture has to be neutralized, resulting in the formation of salts. Because of the low yields of 1-bromo-3,5-difluorobenzene (about 63%) and the high costs of material, this process is of little economic value.
JP 04 182 440 (CA 117: 170951n) describes the isomerization of 1-bromo-2,4-difluorobenzene in the presence of alkali metall t-butoxides or aluminum halides. This process likewise requires an additional, salt-forming neutralization step. The yield of 1-bromo-3,5-difluorobenzene is only 41.4%.
EP 648 724 describes the isomerization of 1-bromo-2,4--difluorobenzene using acidic zeolites as catalysts. Disadvantages of this process are, on the one hand, the large amounts which have to be recycled because of the limited conversion and, on the other, the cost of continuous apparatus.
No other starting materials for the preparation of 1-bromo-3,5-difluorobenzene are described in the literature.
Therefore, there was a need for a process avoiding the disadvantages 10 described and providing an easy industrial route to 1-bromo-3,5-difluoro-benzene in high yields and with high selectivity.
-This object is achieved by a process for preparing 1-bromo-3,5-difluoro-benzene, which comprises converting 3,5-difluoroaniline into its diazonium 15 salt and then converting the diazonium salt in the presence of CuBr and HBr into 1-bromo-3,5-difluorobenzene.
3,5-Difluoroaniline is a known compound. An advantageous way for preparing 3,5-difluoroaniline is described for example in EP 562 435.
The preparation of halogenated aromatic compounds from the - -corresponding anilines is known and comprehensively described in the literature (Sandmeyer reaction). For instance, there are synthetic procedures for the diazotization of anilines and the Sandmeyer reaction of 25 the diazonium salts to the corresponding halogenated aromatic compounds, for example in Organikum, 4th edition (1964), 491/492 and 497/499, Org. Synth., Coll. Vol. 3,185-187, Houben-Weyl, Halogen compounds, Volume V/4 (1960), 438/446. According to these procedures, halogenated aromatic compounds can be prepared in high yields between 30 80 and 95% from the respective anilines.
It is all the more surprising, then, that the technical literature does not -mention the conversion of 3,5-difluoroaniiine into 1-bromo-3,5-difluoro-benzene.
On the other hand, several papers describe the preparation of 1-bromo-3,5-difluorobenzene starting from 2,4-difluoroaniline, an isomer of 3,5-difluoroaniline. 2,4-Difluoroaniline is first converted by bromination into 2-bromo-4,6-difluoroaniline, followed by diazotization with NaNO2 and deamination using hypophosphorous acid in acid solution to give 1-bromo-3,5-difluorobenzene. This pathway involves one more step than the process according to the invention. In addition, yields of the deamination using hypophosphorous acid are substantially lower than the yields for the - Sandmeyer reaction described in the literature.
Since the direct conversion of 3,5-difluoroaniline into 1-bromo-3,5-15 difluorobenzene has not been described, it is reasonable to assume that this reaction can only be carried out with difficulties and that the indirect route via 2,4-difluoroaniline, bromination, diazotization and deamination is more favorable.
20 By contract, it was now been found that, surprisingly, 1-bromo-3,5-difluorobenzene can be prepared in high yield directly from 3,5-difluoroaniline by diazotization and subsequent Sandmeyer reaction.
For the diazotization of 3,5-difluoroaniline with an equimolar amount of 25 NaNO2, a 2.5- to 3-fold excess of HBr is sufficient. It proved useful to add the acid in 48% strength and to carry out the reaction at low temperatures, most favorably at temperatures c1 0C.
NaNO2 is added as about 50% strength solution. By checking the color 30 reaction with starch-iodide paper, it is ensured that no excess nitrite is present. If necess~ry, some urea is added.
The diazonium salt formed is kept at about 10C until further processing.
Either, the entire diazonium salt is added at 0C to the CuBr/HBr, and only then heated to the boil. Or, alternatively, the initially charged CuBr/HBr mixture is heated to the boil and the cooled diazonium salt is added a little at a time, so that the whole mixture is kept at the boil.
The 1-bromo-3,5-difluorobenzene formed is distilled off together with steam. Heating is continued until no further gas is evolved. Then, to recover all the reaction products, the remaining organic product is distilled using steam.
The organic phase is separated off from the aqueous phase, neutralized with dilute alkali metal hydroxide solution, washed, dried and then redistilled to purity.
The following example illustrates the process according to the invention.
Example 1:
Diazotization:
A 500 ml four-neck flask fitted with stirrer, thermometer and dropping funnel is initially charged with 64.5 g (0.5 mol) of 3,5-difluoroaniline and 210 ml of 48% strength HBr (1.25 mol of HBr), and at <10C 34.5 g (0.5 mol) of NaNO2 in 60 ml of water are added with stirring. NaNO2 is added until free HNO2 is just detectable by color reaction with starch-iodide paper.
Sandmeyer reaction:
The reaction mixture kept at 10C is added a little at a time with stirring to aboiling mixture of 35.4 g (0.25 mol) of CuBr in 46 ml of 48% strength HBr (0.27 mol of HBr) in a 1 I four-neck flask fitted with a distillation apparatus,steam-inlet tube, dropping funnel and thermometer. Heating is continued to keep the mixture at the boil. Organic product and water begin to distill over during the addition of diazonium salt. On completion of the addition, steam 5 distillation is continued until no more organic product is collected in the receiving flask.
The phases in the receiving flask are separated, the organic phase is washed first with water, then neutralized with 5% strength NaOH and 10 subsequently washed neutral. After drying over Na2SO4 and redistillation to purity, 80 9 (0.41 mol) of 1-bromo-3,5-difluorobenzene are obtained, equivalent to a yield of 83% of theory.
Claims (7)
1. A process for preparing 1-bromo-3,5-difluorobenzene, which comprises converting 3,5-difluoroaniline into its diazonium salt and then reacting the diazonium salt with HBr in the presence of CuBr.
2. The process as claimed in claim 1, wherein 3,5-difluoroaniline is diazotized with NaNO2 in the presence of HBr.
3. The process as claimed in at least one of claims 1 or 2, wherein the diazotization is carried out with 2.5 to 3 times the molar amount of HBr based on 3,5-difluoroaniline.
4. The process as claimed in at least one of claims 1 to 3, wherein the diazotization is carried out with 48% strength HBr.
5. The process as claimed in at least one of claims 1 to 4, wherein, in the 2nd reaction step, the diazonium salt is added a little at a time to a boiling mixture of CuBr and HBr.
6. The process as claimed in at least one of claims 1 to 5, wherein from 0.2 to 0.5 mol of CuBr is used per mole of 3,5-difluoroaniline.
7. The process as claimed in at least one of claims 1 to 5, wherein, for the 2nd reaction step, from 0.2 to 0.5 mol of Hbr is used per mole of 3,5-difluoroaniline.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19544870A DE19544870C2 (en) | 1995-12-01 | 1995-12-01 | Process for the preparation of 1-bromo-3,5-difluorobenzene |
| DE19544870.7 | 1995-12-01 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2191652A1 true CA2191652A1 (en) | 1997-06-02 |
Family
ID=7778947
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002191652A Abandoned CA2191652A1 (en) | 1995-12-01 | 1996-11-29 | Process for preparing 1-bromo-3,5-difluorobenzene |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0776877B1 (en) |
| JP (1) | JPH09169675A (en) |
| CA (1) | CA2191652A1 (en) |
| DE (2) | DE19544870C2 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB0313110D0 (en) * | 2003-06-07 | 2003-07-09 | Avecia Ltd | Process |
| CN107417488A (en) * | 2017-06-14 | 2017-12-01 | 浙江解氏新材料股份有限公司 | The preparation method of 3,5 difluoro bromobenzenes |
| US20230183154A1 (en) * | 2020-03-12 | 2023-06-15 | Aarti Industries Limited | Process for the preparation of 1-bromo-2,4,5-trifluorobenzene |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS58201734A (en) * | 1982-05-17 | 1983-11-24 | Chisso Corp | 2,4-difluoro-(trans-4'-(trans-4"-alkylcyclohexyl)cyclohexyl) benzene |
| JPH04182440A (en) | 1990-11-16 | 1992-06-30 | Ishihara Sangyo Kaisha Ltd | Production of 3,5-difluoro-1-bromobenzene |
| US5294742A (en) | 1992-03-21 | 1994-03-15 | Hoechst Atkiengesellschaft | Process for preparing 3,5-difluoroaniline |
| US5157169A (en) * | 1992-03-26 | 1992-10-20 | Mallinckrodt Specialty Chemicals Company | Preparation of 3-halo-halobenzenes and 1-halo-3,5-dihalobenzenes |
| GB9223195D0 (en) * | 1992-11-05 | 1992-12-16 | Octel Chem Ltd | Preparation of substituted aryl compounds |
| DE4334437A1 (en) | 1993-10-08 | 1995-04-13 | Hoechst Ag | Process for the preparation of 1-bromo-3,5-difluorobenzene |
| GB9400569D0 (en) * | 1994-01-13 | 1994-03-09 | Rhone Poulenc Chemicals | Process for the production of substituted aromatic hydrocarbons from corresponding anilines by dediazoniation |
-
1995
- 1995-12-01 DE DE19544870A patent/DE19544870C2/en not_active Expired - Fee Related
-
1996
- 1996-11-20 EP EP96118555A patent/EP0776877B1/en not_active Expired - Lifetime
- 1996-11-20 DE DE59603777T patent/DE59603777D1/en not_active Expired - Fee Related
- 1996-11-28 JP JP8317862A patent/JPH09169675A/en not_active Withdrawn
- 1996-11-29 CA CA002191652A patent/CA2191652A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| DE19544870A1 (en) | 1997-06-05 |
| JPH09169675A (en) | 1997-06-30 |
| DE59603777D1 (en) | 2000-01-05 |
| EP0776877B1 (en) | 1999-12-01 |
| EP0776877A1 (en) | 1997-06-04 |
| DE19544870C2 (en) | 1997-09-11 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |