BROMINATION PROCESS

Abstract: A process for partially brominating non-condensing ring aromatics (e.g. diphenyl ether) in the absence of a solvent by adding the polyaromatic to a stoichiometric excess of liquid bromine containing a zirconium halide catalyst. Product containing three bromine atoms per benzene ring (e.g., hexabromodiphenyl ether) is formed in high selectivity by keeping the reaction mixture below a threshhold temperature at which higher bromine substitu­ tion occurs.

Description: Procedures for making perbrominated polyphenylene ethers are known. For example, decabromodiphenyl ether (referred to as "decabrom") is a commercial fire retardant. It can be made by adding molten diphenyl ether to a large stoichiometric excess of liquid bromine containing a halogenation catalyst such as aluminum halide (U. S. 3,965,197). Although it is not a solvent, the large excess of bromine acts as a liquid medium in which the product is suspended and from which it can be readily recovered. In some uses it is preferred to have only a partially brominated flame retardant because it might have more desirable physical properties in a particular substrate. For example a partially brominated diphenyl ether is sold as octabromodiphenyl ether (referred to as "octabrom") although its actual composition is a mixture of partially brominated diphenyl ether. The commercial grade product contains 6-9 bromine atoms per molecule. Using the aluminum halide bromination catalyst as practiced in U. S. 3,965,197, the degree of bromination can only be limited by restricting the amount of bromine to the stoichiometric amount required to insert eight bromine atoms per molecule. Also the product is very colored (yellow to brown) requiring extensive purification if a light colored product is required. In accordance with one embodiment of the invention, non-condensed ring polyaromatics are partially brominated to contain 3-4 bromine atoms per benzene ring by conducting the reaction in a large stoichiometric excess of liquid bromine and using a zirconium halide catalyst which may be promoted with a small amount of iron. The product tends to be much lighter colored than that obtained by adding a stoichiometric amount of bromine to the same polyaromatic compound. In accordance with another embodiment, it has been discovered that by suitably controlling the temperature of the reaction it is possible to introduce three bromine atoms per benzene ring with high selectivity. A preferred embodiment of the invention is a process for making a partially brominated non-condensed ring polyaromatic other than a partially brominated polyphenylene ether, said process comprising reacting said non-condensed ring polyaromatic with bromine in the presence of a catalytic amount of a zirconium halide catalyst, at a temperature from 10°C up to reflux. The preferred polyaromatics of this type can be represented by the formula wherein R is an alkylene group of up to 6 or more carbon atoms, an oxyalkylene group (-O-R-) of up to 6 or more carbon atoms, an oxyalkyleneoxy group (-O-R-O-) of up to 6 or more carbon atoms, a sulfur atom, or a carbon-to-carbon single bond. Some examples of these compounds are: diphenylmethane, 1,2-diphenylethane, benzylphenylether, 1,2-diphenoxyethane, diphenylsulfide diphenyl, 1,4-diphenylbutane. The amount of bromine used is an amount in excess of the stoichiometric amount required to substitute four bromine atoms per benzene ring. The stoichiometric excess can range from 25% up to 500% or more. This means that the amount of bromine ranges from 5 to 24 moles of bromine for each equivalent weight of said polyaromatic, more preferably 6 to 24 moles per equivalent weight of non-condensed ring polyaromatic, wherein an equivalent of non-condensed ring polyaromatic is the molecular weight divided by the number of benzene rings per polyaromatic ring molecule. The excess bromine acts as a liquid reaction medium in which the bromination is conducted. No other solvent is required and it is preferred that no other solvent be used since such use can contaminate the product. The critical feature of the invention is the use of a zirconium halide catalyst rather than the conventional aluminum halide catalyst which causes perbromination. When aluminum halides are used a partially brominated product will not result when using an excess amount of bromine. With aluminum halides the amount of bromine must be restricted to close to the stoichiometric amount. Any zirconium halide can be used such as zirconium chloride, zirconium bromide, zirconium fluoride and mixtures thereof. The most readily available zirconium halide is zirconium tetrachloride. In the reaction mixture the catalytic species is very likely zirconium tetrabromide since large amounts of hydrogen bromide are evolved which can convert any of the zirconium tetrahalides to zirconium tetrabromide. The amount of zirconium halide should be an amount which will catalyze the reaction of bromine with the non-condensed ring polyaromatic to substitute bromine into the aromatic rings. A useful range in which to operate is 0.1 to 10 weight percent based on the amount of bromine. A more preferred range is 0.3 to 5 weight percent based on the bromine charge. The reaction is preferably conducted by charging the bromine and zirconium halide to a reaction vessel and then feeding the non-condensed ring polyaromatic to the liquid bromine. The reaction temperature can range from below ambient (e.g. +10°C) up to reflux temperature under reaction conditions. Although bromine refluxes at about 59°C at atmospheric pressure, the reaction may be conducted at above atmospheric pressure, for example 0.03 to 0.2 MPa, under which conditions reflux temperature will increase. More preferably the reaction is started at the temperature of the charged bromine (e.g. 20 to 30°C) and is permitted to rise during the course of the reaction to a higher temperature (e.g. 30 to 40°C). Heat is then supplied to the reaction mixture to bring the mixture to reflux and speed up the reaction rate. The non-condensed ring polyaromatic may be added to the bromine as a solid or as a liquid. For ease of operation the non-condensed ring polyaromatic is preferably added molten even if this temperature is higher than the bromine temperature or even higher than bromine reflux temperature. The non-condensed ring polyaromatic is added to the bromine over a period of time. Feed time depends on scale and ability to control temperature and handle hydrogen bromide evolution. On a laboratory scale the addition requires 15 minutes to one hour. On a commercial scale, the reaction could take 2 to 8 hours or longer. After completion of the non-condensed ring polyaromatic addition, the reaction mixture can be held for a period to assure the desired degree of bromination has been achieved. A ride period of 4 to 5 hours at or near reflux is beneficial. When an iron promoter is used this time can be shortened. Product can be recovered by any of several conventional methods. For example the reaction mixture can be mixed with water and the excess bromine distilled out. The product can then be recovered from the water by filtration or centrifugation and then dried and ground to the desired particle size. Alternatively, a solvent such as toluene can be added to the water-product mixture to dissolve the product. The solvent phase can be separated and the solvent distilled out leaving the product which is then crushed and ground to a fine powder. In another embodiment of the invention the reaction rate is sharply increased while still controlling the degree of bromination to 3-4 bromine atoms per aromatic ring by conducting the process including a small promoter amount of iron. The iron is preferably added to the bromine in the form of iron particles such as iron powder. The amount of iron can range from 0.01-1.0 gram atom per gram mole of zirconium halide catalyst. A more preferred range is 0.05-0.5 and still more preferred 0.1-0.3 gram atom of iron per mole of zirconium halide. In still another preferred embodiment of this invention the zirconium halide catalyzed reaction is caused to selectively introduce three bromine atoms in the aromatic rings of the non-condensed ring polyaromatic. This is effected by controlling the reaction temperature so that it does not exceed a threshhold temperature at which higher bromine substitution occurs. In conducting this embodiment of the invention without an ancillary solvent, it is preferred to employ at least about 50 mole percent excess of bromine over the stoichiometric amount required to substitute three bromine atoms per aromatic ring. This stoichiometric excess may be as high as 500 percent or more although in most cases the excess will not exceed 200 percent. Preferably the amount of bromine used is 75 to 100 mole percent in excess of the stoichiometric equivalent. The partially brominated non-condensed ring aromatics are useful as flame retardants in a wide variety of organic materials such as polyethylene, polypropylene, polyesters, acrylonitrile-butadiene-styrene terpolymer, polystyrene, high impact polystyrene, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyphenylene ethers and blends of the above. The amount used is generally an amount to provide 5-15 weight percent bromine to the polymer. Synergists, such as antimony oxide, are routinely included.

Claims: A process for making a partially brominated non-condensed ring polyaromatic other than a polyphenylene ether, said process comprising reacting a polyaromatic with bromine in the presence of a catalytic amount of a zirconium halide catalyst at a temperature from 10°C up to reflux wherein said process is conducted using 5 to 24 moles of bromine for each equivalent weight of said polyaromatic, said equivalent weight being the molecular weight of the polyaromatic divided by the number of benzene rings in said polyaromatic. A process of Claim 1 conducted in the substantial absence of a solvent other than liquid bromine. A process of Claim 2 conducted by adding the polyaromatic to the liquid bromine containing the zirconium halide catalyst. A process of Claim 3 wherein said zirconium halide is introduced into said bromine in the form of zirconium chloride.

Inventors: BRACKENRIDGE, DAVID ROSS, MCKINNIE. BONNIE GARY
Applicants: ETHYL CORPORATION
Application year: 1988
Main classification: C07C25
IPC codes: C07C319, C07C17, C07C67, C07C43, C07C323, C07B39, C07B31, C07C41, C07B61, B01J27, C07C25