Claims
- 1. A process for selectively brominating biphenyl in the para positions comprising the step of reacting biphenyl with BrCl in a reaction medium for a time sufficient to form 4-bromobiphenyl, 4-4'-dibromobiphenyl or a mixture thereof.
- 2. The process according to claim 1, wherein the reaction takes place in a medium comprising a solvent.
- 3. The process according to claim 2, wherein BrCl is formed in situ in the reaction medium during the reaction with biphenyl.
- 4. The process according to claim 1, wherein BrCl is formed before its reaction with biphenyl.
- 5. The process according to claim 2, wherein the solvent is selected from halogenated aliphatic hydrocarbons, unhalogenated aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, ethers and nitro solvents.
- 6. The process according to claim 3, wherein the bromine is introduced into the reaction medium in a first step and chlorine is introduced in a second step.
- 7. The process according to claim 3, wherein bromine and chlorine are introduced simultaneously into the reaction medium.
- 8. The process according to claim 3, wherein the reaction is conducted with an excess of bromine relative to chlorine.
- 9. The process according to claim 1, wherein the reaction mixture is brought to a temperature not greater than 5.degree. C. during at least a part of the reaction.
Priority Claims (1)
| Number |
Date |
Country |
Kind |
| 88 08583 |
Jun 1988 |
FRX |
|
Parent Case Info
This application is a continuation of application Ser. No. 07/371,030, filed June 26, 1989, now abandoned.
The present invention relates to a process for bromination of biphenyl with BrCl, and more particularly relates to a process for preparing 4-bromobiphenyl or 4,4'-dibromobiphenyl.
4-Bromobiphenyl is a product capable of many applications. It can be employed in the manufacture of agrochemical or pharmaceutical compounds. It can also be used for the preparation of liquid crystals.
4,4'-Dibromobiphenyl is a compound whose hydrolysis yields 4,4'-dihydroxybiphenyl, the latter product being useful as a monomer for thermotropic polymers.
Thus, both 4-bromobiphenyl and 4,4'-dibromobiphenyl are products which are useful in industrial applications.
One of the problems which arises in preparation of these compounds is that of ring position selectivity, since the object is to obtain products brominated in the 4- or 4,4'-positions.
Therefore, there is a need in the art for a process which is simple, i.e., can be conducted in mild conditions, is selective and has fast kinetics.
It is an object of the present invention to develop a process meeting the above requirements.
The process according to the invention for bromination of biphenyl is characterized in that biphenyl is reacted with BrCl.
The process of the invention makes it possible to obtain yields of at least 60% at ambient temperature and with reaction times on the order of one hour.
Other characteristics and details of the invention will become more clearly apparent upon reading the description and the working examples which follow, no limitation being implied.
A main feature of the process of the invention lies in the use of BrCl as the brominating agent. The process can be implemented according to two alternative embodiments.
A first alternative embodiment comprises forming BrCl before its reaction with biphenyl. In this case, it is possible to employ any known means for manufacturing BrCl.
By way of example, it is possible to form BrCl by bubbling chlorine into HBr or by the action of HCl on an N-bromo derivative such as, for example, N-bromo-N-methylacetamide, N,N-dibromohydantoin, or N-bromosuccinimide in aqueous solution or in organic solution. A preferred method of forming BrCl comprises bubbling chlorine into Br.sub.2 in a solvent solution of CCl.sub.4, CHCl.sub.3, CH.sub.2 Cl.sub.2 or aqueous HCl, for example.
A second alternative embodiment, which is the preferred embodiment, comprises forming BrCl in situ, i.e., BrCl is formed in the reaction medium as the reaction with biphenyl takes place.
In this second embodiment, bromine is preferably introduced into the reaction medium in a first step. In a second step, chlorine is added and the reaction kinetics are simultaneously accelerated.
In accordance with the invention, it would also be possible to introduce bromine and chlorine simultaneously while continually maintaining an excess of bromine relative to chlorine.
In both the first and second alternative embodiments mentioned above, it is preferable to cool the reaction medium to a temperature below or equal to 5.degree. C. In the case of the second alternative embodiment with delayed introduction of bromine and chlorine, this cooling may be carried out after the introduction of bromine and before that of chlorine. The cooling lasts for at least a part of the reaction, preferably throughout its duration. Once the reaction is complete, the temperature is allowed to rise again. Cooling enables BrCl to be kept in a liquid form which makes it easier to control the reaction completely.
In all cases, it is necessary to operate with at least 0.5 equivalent of Br.sub.2 relative to the biphenyl in the case of a monobromination and of at least 1 equivalent of Br.sub.2 relative to the biphenyl in the case of a dibromination. It is quite possible to operate with an excess of bromine relative to the quantities just mentioned. To avoid the interfering chlorination reaction when BrCl is formed in situ, the quantity of chlorine should preferably be smaller than or equal to that of bromine. The specific ratio of bromine to chlorine is selected based on the desired degree of bromination.
The reaction preferably takes place in a medium comprising a solvent. A large number of solvents can be employed and it is preferable that the solvents utilized be inert to bromine and chlorine. The solvent may be selected from the group consisting of halogenated or unhalogenated aliphatic, alicyclic and aromatic hydrocarbons, ethers and nitro solvents.
Examples of usable solvents include hexane, carbon tetrachloride, dichloromethane, trichloromethane, dibromoethane, dichlorobenzene, nitrobenzene, isopropyl ether, hexyl ether and butyl ether.
US Referenced Citations (3)
Foreign Referenced Citations (4)
| Number |
Date |
Country |
| 0331549 |
Sep 1989 |
EPX |
| 1933486 |
Jan 1971 |
DEX |
| 2144259 |
Mar 1972 |
DEX |
| 2950877 |
Jun 1981 |
DEX |
Non-Patent Literature Citations (1)
| Entry |
| Olah et al., "J. Amer. Chem. Soc.", vol. 86(6), pp. 1039, 1046 (1964). |
Continuations (1)
|
Number |
Date |
Country |
| Parent |
371030 |
Jun 1989 |
|
Patent Grant
5107044
