IL98018A - Process for the preparation of 4,4'-dibromobiphenyl - Google Patents

Description

REF : 1825/91 PROCESS FOR THE PREPARATION OF 4,4' -DIBROMOBIPHENYL 98018/2 -1- PROCESS FOR THE PREPARATION OF 4.4'- DIBROMOBIPHENYL The present invention relates to a process for the preparation of 4,4'-dibromobiphenyl. More particularly, the invention relates to a process for the bromination of biphenyl with bromine or hydrobromic acid and their mixtures, in the presence of the oxidizing agent NaBr03, the reaction being carried out in mixtures of water and water-immiscible solvents. 4-4'-Dibromobiphenyl is a well known intermediate to a variety of plastic products. The bromination of biphenyl has been extensively treated in the art. U.S. Patent No. 1,835,754 deals with the bromination of biphenyl in chlorinated aromatic solvents. In this process two moles of bromine are used for each mole needed, and the HBr that is generated in the reaction is not exploited or recycled.

Bromination of solid biphenyl without a solvent has also been attempted [R.E.Buck et al., J. Am. Chem. Soc, 72, 2494 (1950)]. The bromination of biphenyl in the presence of a nitration mixture has also been investigated [B.V. Tarnov et al., in the Izvest. Vysshikh Ucheb. Zavedenii, Khim. I Khim. Tekhnolt. 3, 872-5 (I960)]. The process reported i the latter reference leads to low yields of 4,4'-dibromobiphenyl. Bromination of biphenyl in SO2 [DE 1,930,594] as well as a variety of organic solvents has been attempted [Japan Kokai Tokkoyo Koho 80-64,532]. In all cases, at least two moles of Br2 were used. 98018/3 -2- S. Lin et at. [Environ. Sci. Technol. 18(12) 985-7(1984)] attempted to convert KBr (with NaOCl) into Br2, which was further reacted in situ with biphenyl. However, the authors report the formation of the chloro as well as the bromo-biphenyl compounds in this system. A. Nonn [EP 349,381] attempted the use of BrCl. The use of this reagent leads to two moles of HC1, which must be disposed of.

The gas/solid bromination of biphenyl in the presence of cyclo dextrin was reported by N. Huang et at. [Gaodeng Xuexiao Huaxue Xuebeao 9. (3), 290-1(1980)], but it is only of Limited industrial importance. Biphenyl has also been brominated in the presence of catalysts [EP 319,915 and EP 331,549], but no recovery of HBr in situ has been attempted.

It has now been found, and this is an object of the present invention, that it is possible to react biphenyl with bromine and/or hydrobromic acid in the presence of the oxidizing agent NaBrO ¾, the reaction being carried out in mixtures of water and water-immiscible solvents, and in this way 4,4'-dibromobiphenyl is produced in high yield and very high selectivity, without wasting bromine and without the need for laborious treatment of the final product, to remove excess HBr.

According to the invention, the process for the preparation of 4,4'-dibromobiphenyl comprises reacting biphenyl with bromine and/or with hydrobromic acid in the presence of NaBrO^, in a solvent mixture essentially consisting of water and a water-immiscible organic solvent that is substantially unreactive under the reaction conditions, at a temperature in the range between -10 °C and 100 °C. 98018/2 -3- The bromination of biphenyl leads to the formation of two moles of hydrobromic acid, as described by equation (1) (in which BP stands for biphenyl and DBBP stands for 4,4'-dibromobiphenyl): 3 BP+ 6Br2= 3DBBP + 6HBr (1).

When operating according to the invention, the HBr formed in the reaction described in equation (1) can be reacted with NaBr03, as described in equation (2), thus recycling HBr and liberating bromine into the reaction mixture: 6 HBr+ NaBr03 = 3 Br2 + 3 H20 + NaBr (2).

The use of the oxidant to recycle the HBr requires the presence of water in the reaction mixture, while the presence of organic solvents allows the bromination to be performed at low temperatures, at which the selectivity of the formation of the 4,4'-dibromobiphenyl and the reaction rate are optimized.

According to a preferred embodiment of the invention the organic solvent comprises an aliphatic or aromatic halogenated hydrocarbon, preferably halogenated methanes, ethanes and benzenes. A variety of organic solvents can be used, which is customary in the art of bromination, and which will be recognized by the skilled chemist. Such organic solvent, besides being water-immiscible, should be substantially unreactive under the reaction conditions. A number of representative 98018/2 -4- organic solvents are in the group consisting of CH2CI2, CH2CICH2CI, CH2Br2, CCI2CCI2, C6H5CI and their mixtures. However, as stated, these are by no means the only possible solvents, and they only represent a fraction of the solvents that are useful for this purpose.

According to a preferred embodiment of the invention, the reaction temperature would be in the range between 0° and 70°C. While the reaction according to the invention is very effective, some bromine may be wasted as a result of the need to dispose of the H2O and NaBr that are formed in the re-oxidation of the HBr according to equation (2) above. The bleed of the aqueous phase should be effected only for this purpose. Therefore, the process according to the invention further comprises filtering off the solid product and recycling the solvent mixture to a further reaction step with bleed of excess water formed in the reaction of the NaBr03 with HBr. As will be appreciated by a person skilled in the art, the possibility of recycling the solvent in a simple manner, and of using it in a number of reaction cycles, renders the process of the invention attractive and convenient from the industrial and economic point of view.

The NaBr03 can be introduced at any suitable stage of the reaction, for instance, at the end of the bromination of the biphenyl with Br2, in which case only about half of the bromine required by the stoichiometry of equation 1 is needed, since the other half will be produced by the addition of the calculated amount of NaBr03. Alternatively, NaBr03 can also be added to the reaction mixture at the beginning of the reaction, or at any time during the reaction with bromine, in which case the 1825/91 -5- production time can be considerably shortened. Of course, NaBrO3 can be used to liberate bromine from the HBr in the reaction mixture, whenever HBr becomes available. Thus, for instance, if HBr is added to the reaction, instead of being generated in situ according to equation (1) above, then the process of the invention can still be effected by adding NaBrO^ to the resulting reaction mixture.

The reaction temperature is also an important parameter which affects the reaction rate and selectivity. On the one hand, high selectivity for the 4,4'-dibromobiphenyl is obtained at a relatively low temperature, while high reaction rates are obtained at relatively high temperatures. Therefore, the person skilled in the art will, in all cases, devise a preferred temperature or temperature profile, to obtain the desired selectivity and rate of reaction. For most purposes a purity greater than about 99% is sufficient, which is easily obtained according to the process of the invention, and further purification under these circumstances is unnecessary. This, again, leads to a considerable economic advantage of the process of the invention, as compared to processes of the known art.

The invention will now be illustrated with reference to the following examples, which are not intended to constitute a limitation of the invention. 98018/3 -6- Example 1 Bromination of BP in 1,2-dichloroethane (EDO according- to the prior art Bromine (352 g, 2.2 moles) was added to a stirred solution of biphenyl (154 g, 1.0 mole) in 1,2-dichloroethane (EDC) (300 ml) in a four-necked round-bottomed flask equipped with a stirrer, a condenser, a dropping funnel and a thermometer. To the top of the condenser there was added a trap to absorb HBr released during the reaction. The addition of the Br2 took place over one hour at 5°C after which the reaction mixture was stirred at 50°C for a further five hours. The progress of the reaction and its completion were followed by means of GC analysis. The crude 4,4'- dibromobiphenyl (281 g) was obtained in a yield of 90%. The product was filtered off and washed with dilute Na2SOc¾ solution and water. The organic phase of the filtrate was separated and collected for further use.

GC analyses were conducted on a Varian Model 1 3400. The column used was an HP-1 (100% dimethyl polysiloxane) Megabore 5 m x 0.53 mm at a flow of 8 ml/min. The conditions were an initial temperature of 110°C for one minute, then a rise to 250°C-at 15°/min. giving a retention time for the 4,4'-dibromobiphenyl of 7.6 min.

Example 2 (comparative) Bromination of BP in EDC H2Q Bromine (352 g, 2.2 moles) was added to a stirred solution of biphenyl (154 g, 1.0 mole) in 1,2-dichloroethane (EDC) (200 ml) and H20 (200 ml) in a four-necked, round-bottomed flask equipped with a stirrer, a condenser, a dropping funnel and a thermometer. To the top of the 98018/2 -7- condenser there was attached a trap to absorb HBr released during the reaction. The addition of the Br2 took place over one hour at 20°C, without any noticeable liberation of HBr from the reaction apparatus, after which the reaction mixture was stirred at 50°C for a further five hours. The progress of the reaction and its completion followed the procedure described above. The product was filtered off and washed with dilute Na2S03 solution and water.

The results obtained were comparable to those obtained in Example 1.

Example 3 Bromination of BP in EDC/H20 in the presens of NaBrQ3 Bromine (1 76 g, 1.1 moles) was added to a stirred solution of biphenyl (154 g, 1.0 mole) in 1,2-dichloroethane (EDC) (200 ml), H20 (200 ml) and NaBr03 (54 g, 0.34 mole) in a four-necked, round-bottomed flask equipped with a stirrer, a condenser, a dropping funnel and a thermometer. To the top of the condenser there was added a trap to absorb HBr released during the reaction. The addition of the Br2 took place over one hour at 20°C without any noticeable liberation of HBr from the reaction apparatus, after which the reaction mixture was stirred at 50°C for one further hour. The progress of the reaction and its completion followed the procedure described above. The product was filtered off and washed with dilute Na2S03 solution and water. The filtrate was collected for further use without any additional treatment, except a minor bleed of the excess aqueous phase. The results obtained were comparable to those obtained in Examples 1 and 2. 98018/3 -8- Example 4 Bromination of BP in recycled EDC/H2O in the presence of NaBrOg Bromine (168 g, 1.05 moles) was added to a stirred solution of biphenyl (1 54 g, 1.0 mole) and NaBrOc| (52 g, 0.34 mole) in the filtrate of the previous experiment (Example 3), of which about 60 g of the aqueous phase had been removed for waste treatment, in a four-necked roundbottomed flask equipped with a stirrer, a condenser, a dropping funnel and a thermometer. To the top of the condenser there was added a trap to absorb HBr released during the reaction. The addition of the B¾ took place over one hour at 20°C without any noticeable liberation of HBr from the reaction apparatus, after which the reaction mixture was stirred at 50°C for one further hour. The progress of the reaction and its completion followed the procedure described above. The product was filtered off and washed with dilute Na2SO | solution and water. The filtrate was collected for further use without any additional treatment, except a minor bleed of the excess aqueous phase. The results obtained were essentially the same as those obtained in Example 3.

This procedure was repeated three times without any noticeable change in the purity of the product.

Example 5 Bromination of BP in CHoB^/H O in the presence of NaBrO^ Example 3 was repeated using CH^B^. Similar results were obtained. 98018/2 -9- Example β Bromination of BP in CH2Cl2 H2Q in the presence of NaBrQ3 Example 3 was repeated using CH2CI2. The reaction mixture was refluxed after the completion of the addition of the bromine. Similar results were obtained.

The above description and examples have been given for the purpose of illustration, and are not intended to constitute a limitation of the invention. Many different processes can be effected, using different solvents and mixtures thereof, temperatures, reaction times and procedures, all without exceeding the scope of the invention.

Claims (5)

98018/2 -10- CLA1MS:

1. A process for the preparation of 4,4'-dibromobiphenyl comprising reacting biphenyl with bromine and/or with hydrobromic acid in the presence of NaBr03, in a solvent mixture essentially consisting of water and a water-immiscible organic solvent that is substantially unreactive under the reaction conditions, at a temperature in the range between -10° and 100°C.

2. A process according to claim 1, wherein the organic solvent comprises an aliphatic or aromatic halogenated hydrocarbon.

3. A process according to claim 2, wherein the organic solvent is selected from CH2CI2, CH2CICH2CI, CH2Br2, CCI2CCI2, C6H5CI and their mixtures.

4. A process according to any one of claims 1 to 3, wherein the reaction is carried out in the temperature range between 0° to - 70°C.

5. A process according to any one of claims 1 to 4, further comprising filtering off the solid product and repeating the reaction with the recycled solvent mixture after removing the excess water and NaBr formed in the reaction of NaBr03 with HBr. L U Z 2ATTO 4 L U ZZATTO