GB2178425A - Process for the preparation of decabromodiphenyl ether - Google Patents

Abstract

Decabromodiphenyl ether is prepared by brominating diphenyl ether, in an organic solvent medium, in the presence of a bromination catalyst at room temperature, then refluxing the reaction mixture.

Description

SPECIFICATION Process for the preparation of decabromodiphenyl ether The present invention relates to a process for the preparation of decabromodiphenyl ether of high purity.

A technique for obtaining the brominated derivatives of diphenyl or diphenyl ether has already been described (see, e.g. German Patent DT 1,193,510). In fact, this technique leads to under-brominated compounds, that is to say compounds in which the aromatic rings are only partially substituted with bromine atoms, this bromination being only partial despite the use of an excess of bromine, or of bromine and chlorine, in relation to the stoichiometry.

U.S. Patent 4,287,373 discloses a technique which uses very large quantities of bromine; it has, however, also been proposed to restrict excess to as little as 5% using a special equipment (U.S. Patent 3,752,856).

It has also been proposed (U.S.P. 3,232,959) that the bromination be carried out in an oleum medium, with the disadvantages associated with the manipulation of oleum, the resultant large quantities of sulphuric effluents, the acidity of the product obtained and the low yield.

It has been proposed (U.S.P. 3,959,387) that the bromination be carried out in a solvent medium (methylene bromide) using a homogeneous reaction: according to this technique, the quantity of solvent and the temperature are such that the brominated product remains in solution (whereas in other solvent phase processes, all or part of the brominated product is precipitated in the medium), the perbrominated product being insolubilized by adding methanol to the medium. It can be seen immediately that this technique employs two solvents, with the problems of separation and purification that this involves, before the recycling of the said solvents. Additionally, this technique results in low productivity.

Finally, in European Patent EP 126,569, it has been proposed that the bromination reaction be carried out in a methylene chloride medium. According to this process, the perbrominated product is obtained in a form insoluble in the medium. However, it should be noted that this process requires the use of catalyst in the form of particles of sizes from 5 to 25 mm (recommended particle size) and especially that the diphenyl ether has to be poured into the methylene chloride/bromine mixture in order to avoid the presence of under-brominated compounds or occluded bromine; this technique of pouring results in low productivity in relation to the reactor volume.

Therefore, the present invention, on the other hand, provides a process for the preparation of decabromodiphenyl ether of high purity, that is to say a product with a high deca-substituted compound. This process, noteworthy for its simplicity insofar as the reaction is carried out in a solvent medium and the perbrominated derivative is obtained in a form insoluble in the medium, is also characterized by its excellent productivity which is mainly related to the fact that it does not involve the step mentioned above of introducing the diphenyl ether into the mixture of the solvent and bromine. In addition, the success of the process does not depend on the use of a catalyst of a specific particle size.

According to the present invention there is provided a process for the preparation of decabromodiphenyl ether by reacting a brominating agent with diphenyl ether in an organic solvent medium and in the presence of a bromination catalyst the said process being characterized in that it consists in: a) gradual addition, at room temperature, of the brominating agent to a mixture comprising diphenyl ether, the bromination catalyst and the organic solvent the brominating agent being used slightly in excess (in moles) in relation to the stoichiometry, based on bromine, b) raising the temperature of the medium to the reflux temperature of the organic solvent and maintaining it at this temperature until the perbromination reaction is complete; c) after cooling, treatment of purification of the medium and solid/liquid separation, drying the decabromodiphenyl ether.

The invention employs as the starting product diphenyl ether

It goes without saying that the invention extends to mixtures containing such a product and especially to mixtures of this product with under-brominated diphenyl ethers, that is to say containing less than 10 bromine atoms per molecule.

As used herein, the term used for each type of product (catalyst, brominating agent, solvent) refers, without discrimination, to a single product or a mixture of several products of the same kind.

The brominating agent can be a product known for the bromination of aromatic rings. This agent is advantageously bromine itself.

Various kinds of catalysts have been described in the literature and can be employed in the present process.

U.S. Patent 4,287,373 can be referred to on this matter. Although some metals such as aluminium can be used, aluminium halides and especially a halide, in particular aluminium chloride or bromide, are advantageously chosen. The catalyst may be in the form of particles or agglomerates, and the mean diameter of the particles is typically from 0.05 to 1 5 mm. A non-metallic catalyst may be amorphous or crystalline.

In the present process, the bromination reactions are carried out in an organic solvent medium. In general, the solvent can be halogenated hydrocarbon. Among these, hydrocarbons containing one carbon atom and substituted with bromine and/or chlorine are recommended, preference being given to methylene bromide.

In the process according to the invention, the various agents and reagents listed above are advantageously employed in the following proportions: the bromination catalyst in an amount from 2 to 18% in moles, per mol of diphenyl ether; the solvent in an amount from 3 to 10 moles per mol of diphenyl ether; the brominating agent in an molar excess in relation to the stoichiometry, based on bromine, of up to 10% and preferably 1 to 5%.

In the description of the phase (a) of the process of the invention, the expression "room temperature" should be taken to denote any temperature within the range from 20 to 50,C. The temperature at which phase (b) of the process is carried out depends on the solvent used. Thus, in the specific case of methylene bromide, and for a reaction carried out at atmospheric pressure, the temperature will be of the order of 95-99"C.

As for the temperature of drying of phase (c) of the process, this naturally depends on the solvent used and the conditions of the drying itself. In general the temperature is less than 300"C and preferably from 50 to 250"C according to the conditions chosen (atmospheric pressure or vacuum).

In the process according to the invention, phase (a) consists in the gradual introduction of the brominating agent into the mixture comprising diphenyl ether, the bromination catalyst and the organic solvent. It is advantageous to prepare this mixture in the first place, by incorporation, with stirring, of the diphenyl ether and the catalyst in the organic solvent. Introduction of the brominating agent can be carried out by pouring it, in a continuous or a discontinuous manner, into the said mixture. In general, the duration of this pouring operation, which is advantageously carried out with stirring, is from 1 to 10 hours; these values should be considered only as an order of magnitude.

The maintenance at boiling temperature of the solvent (phase (b)) advantageously lasts 30 minutes to 2 hours.

After cooling the medium obtained in (b) to, say, 20-50"C, the medium may be purified and liquid/solid separation carried out. This involves essentially: deactivation of the catalyst, for example by the addition of water, acidified if appropriate, removal of the excess brominating agent, for example using sodium metabisulphite or hydrazine, one or more stages of washing with water and decantation, filtration of the organic phase containing the perbrominated derivative, draining which enables the recovery of the perbrominated diphenyl ether, on the one hand, and the organic solvent, on the other, which can be recycled and re-used.

The process according to the invention makes it possible to obtain decabromodiphenyl ether of high purity (typically greater than 94%, assay carried out by gas chromatography) with a high yield (typically greater than 95%, relative to the diphenyl ether used at the start).

The Example which follows further illustrates the present invention.

Example: a) 82.6 kg of diphenyl ether and 9.8 kg of aluminium chloride (Al Cl3) are introduced into a reactor containing 547 kg of methylene bromide, with stirring.

808 kg of bromine are poured into this mixture 20 over 5 hours.

The temperature is 28"C at the start of pouring and 48"C at the end of pouring.

b) The temperature is raised to the reflux temperature of the solvent over 1 h 30 min and the medium is maintained at this temperature for 1 hour.

c) The temperature is reduced to 45'C. Water is added to the medium (100 kg) followed by a 24% strength aqueous solution of hydrazine hydrate (36 kg). Decantation and removal of the supernatant aqueous phase containing the deactivated catalyst and hydrobromic acid are carried out, then 4 washings with the same quantity of water (100 kg) followed by decantation, filtration of the organic phase, washing with methylene bromide and drainings are carried out. Drying under vacuum is done at 70"C for 2 hours.

448.5 kg (96.1% yield relative to the diphenyl ether used at the start) of a product containing 94.1% of decabromodiphenyl ether are recovered.

Claims (12)

1. Process for the preparation of decabromodiphenyl ether which comprises: a) gradually mixing, at room temperature (as hereinbefore defined), a brominating agent with a mixture comprising diphenyl ether, a bromination catalyst and an organic solvent, the brominating agent being used slightly in excess (in moles) in relation to the stoichiometry, based on bromine, and b) raising the temperature of the medium to the reflux temperature of the organic solvent and maintaining it at this temperature until the perbromination reaction is complete.

2. Process according to claim 1 which also comprises, after step (b), c) after cooling, purifying the medium, carrying out a solid/liquid separation and drying the decabromodiphenyl ether.

3. Process according to claim 1 or 2 in which the brominating agent is bromine.

4. Process according to any one of claims 1 to 3, in which the bromination catalyst is aluminium chloride or bromide.

5. Process according to any one of claims 1 to 4, in which the organic solvent is a halogenated hydrocarbon.

6. Process according to claim 5, in which the solvent is methylene bromide.

7. Process according to any one of claims 1 to 6, in which the catalyst is used in an amount from 2 to 18%, by mole, per mol of diphenyl ether.

8. Process according to any one of claims 1 to 7, in which the solvent is used in an amount from 3 to 10 moles per mol of diphenyl ether.

9. Process according to any one of claims 1 to 8, in which the molar excess of brominating agent, in relation to the stoichiometry and based on bromine, is up to 10%.

10. Process according to claim 9 in which the said molar excess is 1 to 5%.

11. Process according to claim 1 substantially as described in the Example.

12. Decabromodiphenyl ether whenever prepared by a process as claimed in any one of the preceding claims.