Title of Invention

"AN IMPROVED PROCESS FOR THE PREPARATION OF TETRABROMOBISPHENOL-A"

Abstract

An improved process for the preparation of high quality tetrabromobisphenol-A by reacting bisphenol A with bromine and an oxidant selected from hydrogen peroxide in the presence of an admixture of sodium tungstate with a surface-active agent as a catalyst in a biphasic system, comprising of water and water immiscible organic solvent at a temperature ranging between 20-75°C for 8-15 min under vigorous stirring and separating the organic layer to obtain the tetrabromobisphenol-A by known methods.

Full Text

The present invention relates to an improved process for the preparation of Tetrabromobisphenol-A [4,4'-isopropylidene-bis-(2,6-dibromophenol)]. More particularly, it relates to an eco-friendly process for the preparation of tetrabromobisphenol-A of a very high quality having low APHA color number and lower content of hydrolyzable bromine by bromination of bisphenol A using a catalytic system comprising of an admixture of sodium tungstate with a surface-active agent. Tetrabroraobisphenol-A hereafter referred to as TBBA is one of the most widely used and largest selling brominated flame-retardants in the world. It is used extensively to provide flame retardency for styrenic thermoplastics and for some thermoset resins. The major markets for flame-retardants are the electrical, electronic appliances, automotives, textiles and furniture industry. The high quality TBBA is mandatory for flame-retardant polymers and plastics to be used in the electronics industry. There are several known methods for the manufacture of TBBA, most of them covered in patents. Bromination of bisphenol A (BA) is an essential step in all the methods employed to obtain TBBA. Bromination of BA is conventionally carried out using molecular bromine for the manufacture of TBBA. Since this involves electrophilic bromination, this method generates one mole of hydrogen bromide as an effluent per every mole of molecular bromine consumed. The generated hydrogen bromide on interaction with methanol gives methyl bromide, a widely used fumigant. Therefore, the earlier plants have integrated approach to fulfill the twin objectives of production of TBBA on interaction with molecular bromine and of methyl bromide from methanol employing generated hydrogen bromide.Methyl bromide, a fumigant , which is being banned, necessitates the development of an alternative process to use hydrogen bromide generated in the bromination of BA. In this connection, the function of haloperoxidase enzymes to oxidise the nucleophilic Br" to the electrophilic Br+, observed in nature, inspired us to explore the possibility of oxidising the nucleophile, Br-, of the hydrogen bromide into the electrophilic bromine in order to use liberated HBr in the reaction of bromination of BA for the bromination of BA. Here, we describe a catalytic system comprising of an admixture of sodium tungstate with a surface-active agent that catalyses oxidative bromination in a selective manner. The low cost of the catalyst and its ability to utilise the two atoms of the elemental bromine, raise the prospect of being successful in developing a clean and efficient industrial route to brominated chemicals and drugs. Reference may be made to a US patent 3,536,302, wherein TBBA is formed by reacting bisphenol-A and bromine in methanol. Thus, for the production of tetrabromobisphenol-A, equivalent amounts of HBr are generated. The HBr in turn reacts with the methanol solvent to produce the methyl bromide as a co-product. The drawbacks in the above process are the formation of methyl bromide, which is going to be a banned chemical and that the recovery and reuse of hydrogen bromide is cumbersome. Reference may be made to a Japanese patent 77034620 B4 77/09/05 and US patents 3,929,907; 4,180,684; 5,068,463, wherein the bisphenol-A is brominated in a biphase system comprising of water, water immiscible halogenated organic compound and an oxidant. The oxidant oxidizes the HBr to Br2, which in turn is then available to brominate more bisphenol-A and its under-brominated species. The disadvantages of these processes are longer reaction times and the high expense of handling.In addition. the cooling of the solution to recover tetrabromobisphenol-A entails additional expenditure and process time. Reference may be made to Japanese patent 1979-55538, May 2nd 1979, wherein TBBA was prepared by the bromination of bisphenol-A in the presence of organic solvents and aqueous solutions and an improvement in the product separation was done by incorporating an active surface agent at the end of the reaction, to cause the separation of the emulsion into a distinct phase. The drawback in the above process is that the product is of inferior quality. Reference may be made to US patents 4,990,321; 5,008,469; 5,059,726; and 5,138,103 wherein bisphenol-A is brominated at a low temperature, 0° to 20°C, in the presence of a methanol solvent and a specified amount of water. The amount of water used, however, is not so large so as to cause the precipitation of the tetrabromobisphenol-A from the reaction mass. Additional water for that purpose is added at the end of the reaction. The drawbacks with these processes are that they use a fairly long aging or cooking period after the reactants have all been fed and require an additional process time for the final precipitation of tetrabromobisphenol-A via the last water addition. Reference may be made to a US patent 6,002,050 wherein bisphenol-A saturated with TBBA is brominated in the presence of water, water miscible solvent containing H2O2and 1-20 wt.% of acid at a relatively high temperature. The drawbacks with this process are high temperature, long reaction times, presence of large amount of water and formation of small amounts of methyl bromide. As long as there is a viable market for methyl bromide, the processes have been found to be commercially attractive. However, it is now being proposed, on an international level, that the use of methyl bromide as a fumigant be prohibited. Since the fumigant market is the main market for methyl bromide, a need is apparent for tetrabromobisphenol-A processes which do not co-produce a substantial amount of methyl bromide. This is a difficult task because, to be commercially successful, such processes will be required to economically produce tetrabromobisphenol-A without the benefit of the revenue realized from the sale of the co-product methyl bromide. Obviously, different approaches have been employed to prepare TBBA. Our invention relates to the use of a cheap and easily available catalyst system, an admixture of sodium tungstate and a surface-active agent for the preparation of TBBA. The main object of the present invention is to provide an improved eco-friendly process for the preparation of TBBA of a very high quality from bisphenol A which comprises reacting bisphenol A with bromine and an oxidant hydrogen peroxide in the presence of an admixture of sodium tungstate and a surface-active agent as a catalyst in a biphase system, comprising of water and water immiscible organic solvents at a temperature ranges between 20- 75°C for 8-15 min under vigorous stirring and separating the organic layer to obtain the desired product by known methods which obviates the drawbacks as detailed above. Another object of the of the present invention is addition of bromine in a controlled manner during the period specified. Another object of the of the present invention is vigorous stirring to mix the biphase system properly. Another object of the present invention is the usage of non-corrosive and low cost catalytic system comprising of an admixture of sodium tungstate and a surface-active agent. Still another object of the present invention is the surface-active agent is selected from alkyl benzosulfonic acids, salts of arylnaphthalene sulfonic acids and mixtures thereof. Still another object of the present invention is the catalyst introduced in the system is 2-5 ppm. Still another object of the present invention is the ratio of sodium tungstate and surface-active agent is 1: 4 to 1:9. Still another object of the present invention is the use of water immiscible solvents such as n-pentane, n-hexane, n-octane, methylene chloride, dichloroethane, chlorobenzene and toluene. Still another object of the present invention is the reaction is effected at a temperature in the range of 20 to 75°C for 8 to 10 min. Still another object of the present invention is the amount of bromine is 2.05 to 2.1 moles for mole of bisphenol A. Still another object of the present invention is the amount of hydrogen peroxide is 2.05 to 2.1 moles per mole of bisphenol A. Yet another object of the present invention is an additional step of bleaching of the final product is carried out by sodium sulphite. Accordingly, the present invention provides an improved process for the preparation of tetrabromobisphenol-A of a very high quality from bisphenol A which Accordingly, the present invention provides an improved process for the preparation of high quality tetrabromobisphenol-A which comprises reacting bisphenol A with bromine and an oxidant selected from hydrogen peroxide in the presence of an admixture of sodium tungstate with a surface-active agent as a catalyst in a biphasic system, comprising of water and water immiscible organic solvent such as herein described at a temperature ranging between 20-75°C for 8-15 min under vigorous stirring and separating the organic layer to obtain the tetrabromobisphenol-A by known methods. In an embodiment of the present invention bromine is added in a controlled manner during the period specified. In an embodiment of the present invention vigorous stirring is needed to mix the biphase system properly. In an embodiment of the present invention, the catalyst used is an admixture of sodium tungstate with a surface-active agent. In another embodiment of the present invention, the surface-active agent is selected from alkyl benzosulfonic acids, salts of arylnaphthalene sulfonic acids and mixtures thereof. In yet another embodiment of the present invention, the catalyst introduced in the system is 2-5 ppm. In still another embodiment of the present invention, the ratio of sodium tungstate and surface-active agent is 1:4 to 1:9. In still another embodiment of the present invention, water immiscible solvents used are n-pentane, n-hexane, n-octane, methylene chloride, dichloroethane, chlorobenzene and toluene. In still another embodiment of the present invention, the reaction is effected at a temperature in the range of 20 to 75°C for 8-10 min. In still another embodiment of the present invention, the amount of hydrogen peroxide is 2.05 to 2.1 moles per mole of bisphenol A. In still another embodiment of the present invention, the amount of bromine is 2.05 to 2.1 moles per mole of bisphenol A. In still another embodiment of the present invention, an additional step of bleaching the final product is carried out by sodium sulphite. The catalytic cycle in the bromination of B A to TBBA involves the formation of peroxotungstate on interaction of tungstate with hydrogen peroxide. These peroxy species oxidises Br- of HBr liberated during the reaction of Br2 with B A to electrophilic Br+ to facilitate the electrophilic substitution of BA with the second bromine atom of the bromine molecule. The surface-active agent induces the formation of a stable emulsion out of the immiscible organic layer and water to accelerate the rate of reaction in the biphase reactions. In summing up, sodium tungstate acts as a catalyst in the oxidation of Br" to Br+, while the surface-active agent facilitates all the reactants involved in the bromination to interact at high turnover frequency. The following examples are given by way of illustration of the present invention and therefore should not be construed to limit the scope of the present invention. Example 1 Catalyst Preparation a) Catalyst A: 0.200g of sodium tungstate dihydrate (S.d. fine chem. Ltd.) is dissolved in 20 ml of distilled water and added to the solution of O.8OOg of dodecylbenzenesulfonic acid of the sodium salt, tech (Aldrich) in 20 ml of distilled water under stirring for one hour and evaporated the solution to complete dryness. b) Catalyst B: 0.l00g of sodium tungstate dihydrate (S.d. fine chem. Ltd.) is dissolved in 20 ml of distilled water and added 0.900g of dodecylbenzenesulfonic acid of the sodium salt, tech (Aldrich) in 20 ml of distilled water under stirring for one hour and evaporated the solution to complete dryness. Example 2 100 g of bisphenol A is taken in a 2 litre round bottomed flask together with 600 ml of dichloroethane (DCE), 50 mg of catalyst A, 20ml of water and 62.58 g of 49% hydrogen peroxide and thoroughly stirred. Then 147.4 g of bromine is added continuously over a period of 8-10 minutes using a pressure-equalising runnel. Bromine addition is executed at a controlled manner such that no bromine vapour escapes from the reflux condenser. The reaction mixture is stirred at the same temperature for 5 min. Stirring is terminated and the reaction mass is transferred and allowed to settle in a separating runnel at 60-65°C. Aqueous and organic layers are separated. The organic layer is fed to the same 2 litre flask and 15 g of sodium sulphite dissolved in 700 ml of water is added to the organic layer while stirring The contents are heated in the isomantle to recover DCE. As the DCE is being evaporated, the product separates from the organic layer as a solid. After the DCE recovery, the slurry is filtered to separate the solid product from the aqueous layer. The cake is reslurried with water, stirred for 10-15 min. and filtered. The cake is dried in a vacuum drier. The dried product is TBBA. The purity of the product in this case was 99.72 % TBBA (as determined by HPLC) and the yield of the product was 96.6 %. Example 3 100 g of bisphenol A is taken in a 2 litre round bottomed flask together with 600 ml of dichloroethane (DCE), 50 mg of catalyst B, 20ml of water and 62.58 g of 49% hydrogen peroxide and thoroughly stirred. Then 147.4 g of bromine is added continuously over a period of 8-10 minutes using a pressure-equalising funnel. Bromine addition is executed at a controlled manner such that no bromine vapour escapes from the reflux condenser. The reaction mixture is stirred at the same temperature for 5 min. Stirring is terminated and the reaction mass is transferred and allowed to settle in a separating runnel at 60-65°C. Aqueous and organic layers are separated. The organic layer is fed to the same 2 litre flask and 15 g of sodium sulphite dissolved in 700 ml of water is added to the organic layer while stirring. The contents are heated in the isomantle to recover DCE. As the DCE is being evaporated, the product separates from the organic layer as a solid. After the DCE recovery, the slurry is filtered to separate the solid product from the aqueous layer. The cake is reslurried with water, stirred for 10-15 min. and filtered. The cake is dried in a vacuum drier. The dried product is TBBA. The purity of the product in this case was 99.5 % TBBA (as determined by HPLC) and the yield of the product was 96.6%. Example 4 100 g of bisphenol A is taken in a 2 litre round bottomed flask together with 600 ml of dichloroethane (DCE), 50 mg of catalyst B, 20ml of water and 63.91 g of 49% hydrogen peroxide and thoroughly stirred. Then 143.86 g of bromine is added continuously over a period of 8-10 minutes using a pressure-equalising funnel. Bromine addition is executed at a controlled manner such that no bromine vapour escapes from the reflux condenser. The reaction mixture is stirred at the same temperature for 5 min. Stirring is terminated and the reaction mass is transferred and allowed to settle in a separating funnel at 60-65°C. Aqueous and organic layers are separated. The organic layer is fed to the same 2 litre flask and 15 g of sodium sulphite dissolved in 700 ml of water is added to the organic layer while stirring. The contents are heated in the isomantle to recover DCE. As the DCE is being evaporated, the product separates from the organic layer as a solid. After the DCE recovery, the slurry is filtered to separate the solid product from the aqueous layer. The cake is reslurried with water, stirred for 10-15 min. and filtered. The cake is dried in a vacuum drier. The dried product is TBBA. The purity of the product in this case was 99.88 % TBBA (as determined by HPLC) and the yield of the product was 97 %. Example 5 Recycle experiment: The aqueous layer (60ml) obtained in the example 3 with 10 rng of the fresh catalyst B was used for this recycle experiment. 100 g of bisphenol A is taken in a 2 litre round bottomed flask together with the aqueous layer (60ml) obtained in the example 3 with 10 nig of the fresh catalyst B, 600 ml of dichloroethane (DCE) and 63.91 g of 49% hydrogen peroxide and thoroughly stirred. Then 143.86 g of bromine is added continuously over a period of 8-10 minutes using a pressure-equalismg funnel. Bromine addition is executed at a controlled manner such that no bromine vapour escapes from the reflux condenser. The reaction mixture is stirred at the same temperature for 5 min. Stirring is terminated and the reaction mass is transferred and allowed to settle in a separating funnel at 60-65°C. Aqueous and organic layers are separated. The organic layer is fed to the same 1 litre flask and 15 g of sodium sulphite dissolved in 700 ml of water is added to the organic layer while stirring. The contents are heated in the is omantle to recover DCE. As the DCE is being evaporated, the product separates from the organic layer as a solid. After the DCE recovery, the slurry is filtered to separate the solid product from the aqueous layer. The cake is reslurried with water, stirred for 10-15 min. and filtered. The cake is dried in a vacuum drier. The dried product is TBBA The purity of the product in this case was 99.76 % TBBA (as determined by HPLC) and the yield of the product was 97%. The main advantages of the present invention are: 1. The present process is eco-ftiendly and very simple. 2. The catalyst is cheap, non-corrosive and heterogeneous in nature. 3. Both the atoms of the elemental bromine are utilized with this catalyst. 4. The process is economical. 5. The process is accomplished in a short time. 6. The amount of effluents formed in this process is minimized because the catalyst, solvent and water are recovered /recycled and reused. 7. The process provides high quality of the product. We claim : 1. An improved process for the preparation of high quality tetrabromobisphenol-A which comprises reacting bisphenol A with bromine and an oxidant selected from hydrogen peroxide in the presence of an admixture of sodium tungstate with a surface-active agent as a catalyst in a biphasic system, comprising of water and water immiscible organic solvent such as herein described at a temperature ranging between 20-75°C for 8-15 min under vigorous stirring and separating the organic layer to obtain the tetrabromobisphenol-A by known methods. 2. A process as claimed in claim 1 wherein the surface-active agent used is selected from alkyl benzosulfonic acids, salts of arylnaphthalene sulfonic acids and mixtures thereof. 3. A process as claimed in claims 1-2 wherein the catalyst introduced in the system ranges between 2-5 ppm. 4. A process as claimed in claims 1-3 wherein the ratio of sodium tungstate and surface-active agent is 1:4 to 9:1. 5. A process as claimed in claims 1-4 wherein the reaction is effected at a temperature in the range of 20 to 75°C for 8-10 min. 6. A process as claimed in claims 1-5 wherein the solvents used for the reactions are selected from the group consisting of n-pentane, n-hexane, n- octane, methylene chloride, dichloroethane, chlorobenzene and toluene. 7. A process as claimed in claims 1-6 wherein the amount of bromine is 2.05 to 2.1 moles per mole of TBA. 8. A process as claimed in claims 1-7 wherein the amount of hydrogen peroxide used ranges between 2.05 to 2.1 moles per mole of bisphenol A. 9. An improved process for the preparation of high quality tetrabromobisphenol-A substantially as herein described with reference to examples.

Documents:

728-del-2000-abstract.pdf

728-del-2000-claims.pdf

728-del-2000-correspondence-others.pdf

728-del-2000-correspondence-po.pdf

728-del-2000-description (complete).pdf

728-del-2000-form-1.pdf

728-del-2000-form-19.pdf

728-del-2000-form-2.pdf