IL108961A - Process for the preparation of polybrominated diphenylethanes - Google Patents

Description

108961/2 Ref:2889/93 rrsri-m^ig mum ϋ^ηι "·^! n.DiT? η^ππ PROCESS FOR THE PREPARATION OF POLYBROMINATED DIPHENYLETHANES PROCESS FOR THE PREPARATION OF POLYBROMINATED DIPHENYLETHANES Field of the Invention This invention relates to a process for the preparation of polybrominated diphenyl ethanes, in particular decabromo diphenylethane, and to the products obtained by said process.

Background of the Invention Brorninated diphenylethanes are useful as flame retardants in polymeric compositions, such as polyolefins, polystyrenes and the like. In order to be properly processed and used, these brorninated products should be as pure as possible, should be heat-stable and not undesirably discolored.

Among the polybrominated diphenyl ethanes, decabromo diphenylethanes are particularly preferred and various methods for their preparation are known in the prior art.

According to USP 5,008,477, corresponding to IL 97,620, polybrominated diphenylalkanes, which predominantly contain decabromo diphenylalkanes, in particular decabromo diphenylethane, are prepared by bromination from the corresponding diphenylalkanes.

In Japanese Kokai 55-79325, a method for the dimerization of halogenated organic compounds is disclosed, which comprises treating the starting compounds with iron powder in the presence of a polyoxyethyleneglycol derivative of the general formula RO(C2H40)nR' , wherein R and R' are hydrogen or a hydrocarbon radical and n is comprised between 4 and 100 The methods of the prior art, when applied to the manufacture of polybromo diphenylethanes, are not fully satisfactory either as to yield, or as to purity of the final product, or as to simplicity and efficiency of the process.

It is a purpose of this invention to provide a method for preparing polybromo diphenylethanes that eliminates all the defects of the prior art processes.

It is another purpose of the invention to provide such a method which produces highly pure products.

It is a further purpose of this process.to provide products that are heat-table and that have all the other desirable qualities for processing and using them in the art.

Other purposes and advantages of the invention will appear as the description proceeds.

Summary of the Invention The process according to the invention is characterized in that, in order to prepare a desired polybrominated diphenylethane, the corresponding brominated benzylbromides are condensed in a solvent chosen from among diethylene glycol dimethyl ether (diglyme) and ethylene glycol dimethyl ether in the presence of an iron compound.

If the end product has the general formula wherein m and n are whole numbers, each one up to 5 (and particularly 3 to 5), the starting products are bromobenzylbromides. If m = n, the reaction is dimerization and if the final product is decabromo diphenylethane, the starting product will be pentabromobenzylbromide.

The iron reagent is preferably chosen from among Fe, preferably as a powder, Fe/FeCl3 and Fe NiBr2, or a combination thereof.

Detailed Description of Preferred Embodiments The dimerization of the starting n-bromobenzylbromide is preferably carried out under stirring. The reaction temperatures may vary from 60 to 180°C, and are preferably in the vicinity of 100°C.

Example 1 Preparation of hexabromo diphenylethane Into a three-necked flask having a volume of 250 ml, provided with a mechanical stirrer, condenser and thermometer, dried under vacuum, 45 g (0.1 mole) tribromobenzylbromide are introduced together with 50 ml of diglyme and 550 mg of iron chloride and 445 g (80 mmoles) of iron powder.

The reaction mass is heated in a nitrogen atmosphere up to 100°C and is stirred for about 10 hours, whereafter the solvent is evaporated under vacuum. The powder which is thus obtained is washed several times in a aqueous 10% HCl solution to remove the iron. Thereafter it is washed with citric acid and water and is dried until its weight becomes stable.

The product obtained has a melting point of 204-206°C, a TGA weight loss of 2% at 245°C and 5% at 275°C (the heating rate is 10°C per minute in nitrogen atmosphere). By GC analysis a surface percentage of 95-96 of hexabromodiphenylethane is detei-mined.

Example 2 Preparation of octabromo diphenylethane Proceeding as in Example 1 , 49 g (0.1 mole) of tetrabromobenzylbromide are treated. After evaporation of the solvent, the solid obtained is washed with a solution of HCl to remove the iron, and with dibromoethane. After drying, a product is obtained which has a melting point of 246-247°C, a TGA weight loss of 2% at 270°C and 5% at 310°C.

Example 3 Preparation of decabromo diphenylethane The apparatus used is a 1 -liter flask provided with a stirrer, thermometer and a condenser, which is dried under nitrogen. The following materials are charged: 600 g of pentabromobenzylbromide, 500 ml of diglyme, 45 g of iron powder and 0.65 g of NiBr2. The reaction mixture is heated to 100°C for 6 hours. At the end of the reaction, the reaction mass is cooled to room temperature and is filtered. The solid thus obtained is reintroduced into the reaction apparatus, 1 liter dibromomethane with 10% HCl solution and once with water. The product is filtered and dried until its weight becomes stable.

The resulting product has a melting point of 336-338°C. The Y. I. is below 10. By GC analysis the content of decabromo diphenylethane is found to be 95%. The weight loss is 5% by TGA at a temperature of 310°C and the conversion obtained is 95%.

The reaction may be represented as follows: While embodiments of the invention have been described by way of illustration, it should be understood that they are not limitative and that the invention may be carried out with many modifications, variations and adaptations by persons skilled in the art, without departing from its spirit or exceeding the scope of the claims. 108961/3 -6-

Claims (12)

1. · Process for the preparation of polybrominated diphenylethanes, characterized in that the brominated benzylbromides are condensed in a solvent chosen from among diethylene glycol dimethyl ether and ethylene glycol dimethyl ether in the presence of an iron reagent.

2. - Process according to claim 1, comprising preparing polybrominated diphenylethanes having the general formula by condensing brominated benzylbromides having the general formula wherein m, n and p are each whole numbers; p is partially n and partially m; in the event that m=n then p=m=n; and m+n equals or is greater than 6.

3. - Process according to claim 2, comprising preparing polybrominated diphenylethanes having the general formula wherein n is a whole number from 1 to 5.

4. · A process according to claim 3, wherein n is a whole number from 3 to 5.

5. · Process according to claim 1, wherein the iron catalyst is chosen from among Fe, Fe/FeCla and Fe/NiBr2. 2889/93 -7-

6. - Process according to claim 1 , wherein the reaction is carried out at temperatures in which the starting benzylbromide is soluble or partly soluble in the solvent.

7. - Process according to claim 1 , wherein the final product is decabromo diphenylethane and the starting product is pentabromobenzylbromide.

8. - Process according to claim 1 , wherein the dimerization is carried out under stirring.

9. - Process according to claim 1 , wherein the reaction temperatures are comprised between 60 and 180°C.

10. - Pure polybrominated diphenylethanes, obtained by a process according to claim 1.

11. - Process for the preparation of polybrominated diphenylethanes, substantially as described and exemplified.

12. - Pure polybrominated diphenylethanes, substantially as described and exemplified. LUZZATTO ft LUZZATTO