PREPARATION OF HEXABROMOCYCLODODECANE

Abstract: Hexabromocyclododecane may be synthesized at a high yield in pure form by brominating 1,5,9-cyclododecatriene with bromine in a C₄-C₈ saturated aliphatic alcohol in the presence of a boron trifluoride complex, neutralizing the reaction mixture with a non-aqueous base, and recovering the resulting crystals of hexabromocyclododecane.

Description: BACKGROUND OF THE INVENTION This invention relates to a method for preparing hexabromocyclododecane. Hexabromocyclododecane has been widely used as a flame retardant for molded or foamed thermoplastic products such as those made of polyolefin or polystyrene. It also finds use in the fireproofing treatment of textile products in the form of a latex or water-suspension. Hexabromocyclododecane may be synthesized by brominating 1,5,9-cyclododecatriene. It is desirable for the resulting product to be colorless and free of low melting point by-products as far as possible, particularly when it is intended for use with high impact strength polystyrene resins comprising polyolefin, polystyrene and styrene-butadiene copolymer. In the conventional process, the bromination of 1,5,9-cyclododecatriene is carried out in a solvent such as ethanol. The mother liquor from which crystals of the result­ ing hexabromocyclododecane are separated is reused in the next bromination reaction. This known process, however, must suffer from certain disadvantages in that the product is contaminated with significant amounts of low melting point by-products. Further purification requires washing the raw product with a large amount of solvent such as clean ethanol one or several times. This, of course, increases cost while decreasing the yield of pure product. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved method for producing hexabromocyclododecane which gives the product in purer form at higher yields. This and other objects are accomplished by providing a method for preparing hexabromocyclododecane which comprises the steps of reacting 1,5,9-cyclododecatriene with bromine in a C₄-C₈ saturated aliphatic alcohol in the presence of a catalytically effective amount of a boron trifluoride complex, neutralizing the reaction mixture with a non-aqueous base, and recovering the resulting crystals of hexabromoyclododecane. DETAILED DISCUSSION The method of the present invention is characterized by the use of a C₄-C₈ saturated aliphatic alcohol as a reaction solvent as well as the use of a boron trifluoride complex as a catalyst in the bromination of 1,5,9-cyclododecatriene. The alcohol usable for this purpose preferably have a solubility parameter (S.P.) of about 9.2 to about 11.5. They may be straight or branched chain alkanols or an cycloalkanol having 4-8 carbon atoms. Examples thereof include n-butyl alcohol (S.P. 10.7), isobutyl alcohol (S.P. 10.8), n-amyl alcohol (S.P. 10.6), isoamyl alcohol (S.P. 10.0), n-hexyl alcohol (S.P. 10.0), cyclohexanol (S.P. 11.4) and n-octyl alcohol (S.P. 10.3). Mixtures of these alcohols such as fusel oil (S.P. 10.3) may also be used. Examples of boron trifluoride complexes include boron trifluoride-ethyl ether complex, boron trifluoride-phenol complex, boron trifluoride-amine complexes, boron trifluoride-­ methanol complex and boron trifluoride-acetic acid complex. The amount of the above reaction solvent is not critical provided that the exothermic reaction may be conveniently controlled. The amount of boron trifluoride complex catalyst is generally from 0.5 to 2%, preferably about 1% by weight of the solvent. The amount of bromine ranges between 3.0 and 3.2 moles as Br₂ per mole of 1,5,9-cyclododecatriene. This amount of bromine may be added dropwise to the mixture of 1,5,9-cyclododecatriene and the solvent containing the catalyst. Alternatively, bromine may be added concurrently with 1,5,9-cyclododecatriene to the reaction solvent con­ taining the catalyst. The reaction temperature may be below 40°C, prefer­ ably below 30°C. After the completion of the bromination reaction, the reaction mixture is neutralized to a pH about 8.0 to 8.5 with an amount of non-aqueous base such as a solution of sodium methoxide, sodium ethoxide, potassium butoxide, sodium iso­ butoxide or sodium isoamyloxide in the corresponding alcohol, triethylamine, triethanolamine, diethanolamine, monoethanol­ amine, butylamine, ethylamine, cyclohexylamine, trimethylamine, pyridine or alcoholic solutions of these amines or ammonia. After the neutralization, crystals of hexabromocyclo­ dodecane are filtered off and washed thoroughly with hot water or hot lower alkanol or both. The crystals may be washed further with dilute aquous ammonia if necessary. After drying, hexabromocyclododecane may be obtained at a high yield in a pure state. The following examples illustrate the invention. All parts and percents therein are by weight unless otherwise indicated. EXAMPLE 1 A flask was charged with 420g of isobutyl alcohol containing 4.2g of boron trifluoride-ethyl ether complex. Then 495g (3.09 mols) of bromine and 162g (1 mol) of 1,5,9-cyclododecatriene were concurrently added dropwise to the flask while maintaining the temperature at 20-30°C. After the addition, the reaction mixture was stirred for 2 hours and then cooled to 20°C. The mixture was neutralized to pH8.0-8.5 with 20% solution of sodium methoxide in methanol. The resulting crystals were filtered off, washed with 320g of boiling methanol and then 1% aqueous ammonia successively, and dried at 50°C. 559g (87% of theory) of hexabromocyclo­ dodecane was obtained. Properties of the product are shown in Table 1. EXAMPLES 2-3 AND COMPARATIVE EXAMPLES 1-2. The procedure of Example 1 was repeated except that the solvent and catalyst were substituted with other solvents and catalysts listed in Table 1. The results are also shown in Table 1. EXAMPLES 4-6 AND COMPARATIVE EXAMPLES 3-4 Using various solvents and catalysts listed in Table 2, the procedure of Example 1 was repeated. However, whole amount of cyclododecatriene was charged initially and only bromine was added dropwise. The results are shown in Table 2. EXAMPLES 7-8 AND COMPARATIVE EXAMPLES 5-6 Using various solvents, catalysts and neutralizing agents listed in Table 3, the procedure of Example 1 was repeated. However, crystals recovered from the neutralized mixture were washed with 400g of boiling water containing a small amount of aqueous ammonia and dried at 50-80°C. The results are shown in Table 3. APPLICATION EXAMPLE 100 parts of polystyrene resin, 3.5 parts of hexabromocyclododecane obtained in the above Example 1, 2 or 4 or comparative Example 1 or 4, 0.03 parts of di-n-octyl maleate polymer and 0.03 parts of dioctylphenyl phoshite were kneaded on a hot roll mill at 180-190°C for 6 minutes. The resulting compound was pressed into a sheet at 180-190°C at 200 atms for 3 minutes and cooled. Each specimen was tested for color change, flame retardancy (oxygen index) and viscosity change. The results are shown in Table 4.

Claims: 1. A method for preparing hexabromocyclododecane which comprises the steps of reacting 1,5,9-cyclododecatriene with bromine in a C₄-C₈ saturated aliphatic alcohol in the presence of a catalytically effective amount of a boron trifluoride complex, neutralizing the reaction mixture with a non-aqueous base, and recovering the resulting crystals of hexabromocyclododecane. 2. The method according to Claim 1, wherein said alcohol has a solubility parameter of 9.2 to 11.5. 3. The method according to Claim 1, wherein said alcohol is n- or iso-butyl alcohol, n- or isoamyl alcohol, n-hexyl alcohol, n-octyl alcohol, cyclohexanol or mixtures thereof. 4. The method according to Claim 1, wherein said boron trifluorid complex is the complex with a lower alkyl ether, an amine, phenol, methanol or acetic acid. 5. The method according to Claim 1, wherein said non-aqueous base is a solution of alkali metal lower alkoxide in the corresponding alcohol, an amine or a solution of said amine or ammonia in a lower alkanol. 6. The method according to Claim 1 further including the step of washing said crystals with hot water or hot lower alkanol.

Inventors: NAKANO, TAKUJI, NISHIBORI, SETSUO, TANIUCHI, AKIRA
Applicants: DAI-ICHI KOGYO SEIYAKU CO., LTD.
Application year: 1988
Main classification: C07C23
IPC codes: B01J31, C07C67, C07C23, C07C17, C07B61