Instantaneous, Facile and Selective Synthesis of Tetrabromobisphenol A using Potassium Tribromide: An Efficient and Renewable Brominating Agent Lalit Kumar,* Vivek Sharma, Tanu Mahajan, and D. D. Agarwal Department of Industrial Chemistry, Jiwaji UniVersity, Gwalior-474011, Madhya Pradesh, India Abstract: An instantaneous method for the bromination of bisphenol A has been reported using potassium tribromide for the first time as an efficient brominating agent affording the corresponding tetrabro- mobisphenol A in a reaction time of only 5-10 min at ambient temperature in high yields (99%) and purity (>99%), free from reaction byproduct and having very low ionic impurities. Mild reaction conditions and simple workup provide a practical and commercially viable route for the synthesis of the largest selling flame retardant. The generated HBr during the bromination reaction is used either in the preparation of value-added bromi- nated products or is disposed of as waste, causing serious environmental problems. An environmentally acceptable method for an inbuilt recycling of HBr by its neutralisation, thereby generating additional amounts of metal bromide and recovering the solvent from the liquid mixture has been designed and developed. The KBr used for the preparation of potassium tribromide can be recovered, regenerated in additional amounts, and reused without any significant loss. Introduction Flame retardants are substances that can be chemically inserted or be physically blended into polymers to reduce, delay, or modify the propagation of a flame. There are several classes of flame retardants: 1 halogenated hydrocarbons (chlorine- and bromine-containing compounds and reactive flame retardants), inorganic flame retardants (boron compounds, antimony oxides, aluminium hydroxide, molybdenum compounds, zinc and magnesium oxides), phosphorous-containing compounds (or- ganic phosphate esters, phosphates, halogenated phosphorus compounds and inorganic phosphorus containing salts). Tetrabromobisphenol A (TBBPA), chemical name 4,4′- isopropylidine-bis-(2,6-dibromophenol) is a specialty chemical with a wide range of applications in industries. It is used as a reactive flame retardant in epoxy, vinyl esters, polystyrenes, phenolic resins, and polycarbonate resins. Tetrabromobisphenol A may also be used as a parent compound for the production of other commercial flame retardants, such as tetrabromobisphe- nol A bis (2-hydroxyethyl ether), tetrabromobisphenol A dibromopropylether, tetrabromobisphenol A bis (allylether), tetrabromobisphenol A carbonate oligomers, and tetrabromo- bisphenol A brominated epoxy oligomer. Scientific Studies of TBBPA. 2,3 TBBPA is fully recyclable and complies with all legislation for recycling and recovery. According to an article in Dataweek 2009, 18 February, the European Commission is unlikely to add tetrabromobisphenol A (TBBPA) to the list of substances monitored or banned under RoHS (Restriction of Hazardous Substances). Recent studies revealed that processes used for the production of TBBPA fall into the following categories. The first category 4 includes processes in which bromination of bisphenol A was carried out at 20-30 °C with bromine in aq acetic acid reaction medium. The main disadvantages were that the process requires postheating of the reaction mass at 80-120 °C and the process suffered from the problem of relatively low yield (81.5%) which makes the process cumber- some and unsuitable for manufacturing-scale operations. The second category 5 involves the process in which bisphe- nol was reacted with bromine in the presence of alkali metal chlorate as oxidant in methanol. Disadvantages of the process lie in its low economics as the process requires mineral acid to increase the reaction rate and a strong oxidant such as NaClO 3 which are the major drawbacks. The third category 6,7 includes processes reacting bisphenol and bromine in methanol solvent. The HBr produced during reaction reacts with the methanol to produce methyl bromide coproduct. Generally, up to 40-50 kg of methyl bromide can be expected per 100 kg of tetrabromobisphenol A produced. After the bisphenol A and bromine feed are finished, the reactor contents are cooked for 1-2 h to complete the reaction. The drawbacks in the above process are the formation of methyl bromide, 7 which is going to be a banned chemical 9,11 and that the recovery and reuse of hydrogen bromide is cumbersome. The fourth category 8-11 of processes features the production of tetrabromobisphenol A without the coproduction of substan- tial amounts of methyl bromide and without the use of oxidants to convert the HBr to Br 2 . Generally, these processes brominate * To whom correspondence should be addressed. Telephone: +91-9993267029. E-mail: lalitkumar0108@gmail.com. (1) Lindemann, R. F. Ind. Eng. Chem. 1969, 69, 70. (2) Velu, S.; Kumar, V. R.; Narayanan, A.; Swamy, C. S. J. Mater. Sci. 1997, 32, 957. (3) TBBPA unlikely to be banned under Restriction of Hazardous Substances (RoHS). DATAWEEK Electron. Commun. Technol. 2009, 18 February, http://dataweek.co.za/article.aspx?pklArticleId)5580& pklCategoryId)31. (4) Brackenridge, D. R. Process for halogenating a bisphenol. U.S. Patent 4,013,728, 1977. (5) Swietoslawaski, J.; Silowiecki, A.; Ratajczak, A.; Nocon, K.; Baniak, Z. Process for production of 4,4′-isopropylidene-bis-2,6-dibromo- diphenol. U.S. Patent 4,112,242, 1978. (6) Noonam, A. P.; Scherrer, S. C. Process for the manufacture of tetrabromobisphenol A with coproduction of n-propyl bromide. U.S. Patent 6,049,014, 2000. (7) Mc Kinnie, B. G.; Sharp, G. L.; Williams, R. E. Process for high purity tetrabromobisphenol A. U.S. Patent 5,283,375, 1994. Organic Process Research & Development 2010, 14, 174–179 174 • Vol. 14, No. 1, 2010 / Organic Process Research & Development 10.1021/op900262f  2010 American Chemical Society Published on Web 12/30/2009