SYNTHESIS OF PERFLUORO AROMATIC BORANES AND BORATES

Abstract: A method for synthesizing bromopentafluorobenzene from hexafluorobenzene is described.

Description: SYNTHESIS OF PERFLUORO AROMATIC BORANES AND BORATES This application is a continuation-in-part of application Serial No. 08/736,655 filed October 25, 1996, application Serial No. 08/751,985 filed November 19, 1996 and application Serial No. 08/754,622 filed November 21, 1996. FIELD OF THE INVENTION This invention relates to the preparation of certain fluoroaromatic compounds and to related boranes and borates. More particularly, the invention relates to the preparation of bromopentafluorobenzene from hexafluorobenzene and to bromopentafluoro boranes and borates. BACKGROUND OF THE INVENTION Various metallocene olefin polymerization catalysts comprise a pentafluorophenyl group frequently derived from expensive bromopentafluorobenzene. Accordingly, there is a need for a cost-effective method for converting readily available hexafluorobenzene to bromopentafluorobenzene . Pentafluorobenzene magnesium halides (Grignard reagents) are known. Repress, et al . J. Orσanometallic Che . (1969) 18:263-274 and Repress, et al . , J. Orσanometallic Chem. (1969) .18:191-195 and United States patent 5,362,423. This synthesis is illustrated by Equation 1: C 6 F 6 + 2 EtMgBr F_eC_l 2 → c F MgX + MgX + es THF/Et 2 0 a (1) (Prior Art! in which the three X's indicate two bromine atoms and one fluorine atom. The distribution of the bromine and fluorine atoms between the Grignard and the magnesium salt is not presently known. SUMMARY OF THE INVENTION Pursuant to the invention bromopentafluorobenzene is synthesized by quenching a pentafluorobenzene magnesium halide with a halogenating agent, preferably bromine. DETAILED DESCRIPTION OF THE INVENTION In a specific embodiment, this invention entails reaction of the C 6 F 5 MgX Grignard (see Equation 1) preferably in the vessel in which it is produced, with a halogenating agent, heat or in solution, in a non- interfering solvent to produce bromopentafluorobenzene. In generic embodiments of the invention, any Grignard reactant is used in the Equation 1 reaction which has the formula RMgY in which R is a hydrocarbyl radical containing a beta-hydrogen and Y is any halogen, i.e., fluorine, chlorine, bromine or iodine. FeCl 2 C 6 F 6 + 2 RMgY *. THF/Et 2 0 C 6 F 5 MgY + MgY 2 + gases ( 2 ) In the formula RMgY, Y is halogen, and preferably bromine or iodine and R is a C x to C 20 , and preferably a C 2 to C 10 , hydrocarbyl group such as, for example ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, including their branched chain iso ers such as, for example, isopropyl, sec-butyl, tert-butyl, isobutyl, isopentyl, and cyclic alkyls such as for example, cyclohexyl and the like. The C 6 F 5 MgY product is quenched, preferably in the Equation 2 reaction mixture, with a halogenating agent, heat or in solution in non- interfering, preferably a hydrocarbon or chlorinated hydrocarbon solvent to produce a first reaction mixture containing bromopentafluorobenzene. Useful halogenating agents include elemental bromine chlorine and iodine, carbon tetrachloride, carbon tetrabromide, chloroform, bromoform, and n-bromo or n-chloro succinamide. Elemental bromine is preferred. The halogenating agent is added in an amount at least stoichiometric with respect to the pentafluorophenyl magnesium bromide. Preferably, the halogenating agent is added in an amount within ninety (90%) percent of the stoichiometric amount. Suitable halogenating agent solvents are straight or branched chain, five to ten carbon atom, aliphatic hydrocarbons, benzene, toluene, and two to ten carbon atom halogenated aliphatic hydrocarbons . Methylene chloride is preferred. EXAMPLE 1 In a 2 1, N 2 purged flask were combined hexafluorobenzene (145 g) , FeCl 2 (0.8 g) and THF (600 ml). The solution was cooled to 0-5°C, and ethyl magnesium bromide (3.12 M in Et 2 0, 500 ml) was then added dropwise. After the addition was complete, the reaction mixture was stirred for one-half hour. A solution of bromine (125 g) in methylene chloride (250 ml) was then added dropwise to the cold (0-5°C) reaction mixture. After stirring 15 minutes, 4 N HC1 was added until all solids were dissolved. The two phases were separated and the organics were washed sequentially with water, aqueous sodium bicarbonate and brine. After drying over sodium sulf te, the mixture was distilled providing 160 g of C 6 F 5 Br (83% yield) . The reaction mixture may also be reacted directly after removal of methylene chloride and otherwise without isolation of the C 6 F 5 Br with butyl lithium to produce C 6 F 5 Li which, in turn, is reacted with BC1 3 or BF 3 to produce (C 6 F 5 ) 3 Br.

Claims: I CLAIM : 1. A method which comprises reacting C 6 F 5 MgY in which Y is F, Cl, Br, I with a halogenating agent to produce a halopentafluorobenzene which has the formula C 6 F 5 X in which X is a chlorine, bromine or iodine. 2. The claim 1 method in which the halogenating agent is bromine, chlorine, iodine, carbon tetrachloride, carbon tetrabromide, chloroform, bromoform, or an n-bromo or n-chloro succinamide. 3. A method which comprises reacting C 6 F 5 MgY in which Y is F, Cl, Br, I with bromine to produce bromopentafluorobenzene . 4. A method for converting hexafluorobenzene (C 6 F 6 ) to bromopentafluorobenzene (C 6 F 5 Br) which comprises: (i) converting C 6 F 6 to C 6 F 5 MgY in which Y is F, Cl, Br, I , and (ii) reacting said C 6 F 5 MgY of step (i) with a halogenating agent in a non-interfering solvent, to provide a reaction mixture containing bromopentafluorobenzene in solution in said solvent. 5. The claim 4 method further comprising: (iii) isolating said bromopentafluorobenzene from said step (ii) reaction mixture. 6. The claim 4 or claim 5 method in which said step (ii) non-interfering solvent is a 2 to 10 carbon atom hydrocarbon or a halogenated hydrocarbon. 7. A method which comprises (i) reacting C 6 F 6 with ethyl magnesium bromide in a medium comprising ethyl ether and tetrahydrofuran to produce C 6 F 5 MgBr in solution in said medium; (ii) reacting said C 6 F 5 MgBr with bromine wherein C 6 F 5 Br is produced. 8. The claim 7 method further comprising (iii) isolating said C 6 F 5 Br produced in step (ii) . 9. The claim 8 method further comprising: (iv) reacting said C 6 F 5 Br isolated in step (iii) with n-butyl lithium to convert said C 6 F 5 Br to C 6 F 5 Li.

Inventors: ASKHAM FREDRIC, ASKHAM, FREDRIC
Applicants: ASKHAM FREDRIC, BOULDER SCIENT CO, ASKHAM, FREDRIC, BOULDER SCIENTIFIC COMPANY
Application year: 1997
Main classification: C07C25
IPC codes: C07C17, C07C25, C07F1, C07F5