Process for the preparation of halogen-containing aromatic compounds
DESCRIPTION: 
     The invention relates to a process for the preparation of halogen-containing aromatic compounds which contain at least two aromatic rings which are bonded to one another via at least one bridging member. 
     The preparation of 1,4-bis-(4-chlorobenzoyl)-benzene is disclosed in GB Pat. 1,139,296, where 700 parts (6.22 mol) of chlorobenzene are reacted at 130° C. in the course of 6 hours with 97 parts (0.48 mol) of terephthaloyl dichloride and 145 parts (1.09 mol) of powdered anhydrous aluminum chloride. A yield is not reported. The analogous reaction of fluorobenzene is described, inter alia, in DE-A-3,531,837, the halobenzene (in this case fluorobenzene), aluminum chloride and terephthaloyl dichloride being used in virtually the same molar ratios as in GB Pat. 1,139,296. However, the yield reported for 1,4-bis-(4-fluorobenzoyl)-benzene in DE-A-3,531,837 is dubious since more product is obtained after purification (1250 g) than was present as crude product (1225 g). Also, the melting incorrectly reported as 121° C. (instead of 218.5° to 219.5° C. according to Hergenrother et al. in Journ. Pol. Sci., part A, Polymer Chemistry, 25, 1094 (1987)). 
     It is a disadvantage of all previously known processes that a large amount of aluminum trichloride must be employed which must be led off with the effluent during working-up and pollutes the same. This also applies to the other Lewis acids iron chloride, titanium tetrachloride and tin tetrachloride mentioned in DE-A-3,531,837. It is therefore desirable to develop a process where the catalyst systems are easily worked up and can be recovered. 
     The present invention accordingly provides a process for the preparation of halogen-containing aromatic compounds of the formula ##STR2## in which: Hal denotes halogen, 
     R denotes H, C 1  -C 1  -alkyl, phenyl, halogen or trifluoromethyl, 
     Y denotes CO or SO 2  and 
     Z denotes an aromatic or heteroaromatic grouping, where 
     Y-Z-Y together also denote CO or SO 2 , which comprises reacting a halomatic of the formula RC 6  H 4  Hal (II) is reacted with a bis(acid halide) of the formula Hal-Y-Z-Y-Hal (III) in a molar ratio of at least 2:1 in the presence of hydrogen fluoride and boron trifluoride, in which in the formulae II and III Hal, R, Y and Z have the previously given meaning. 
     Preference is given to the preparation of compounds I which meet at least one of the features that Hal is fluorine or chlorine, R is hydrogen or halogen, Y is CO and Z is phenylene and, in particular, p-phenylene and that halogen is in a position other than the o-position to Y. Compounds having halogen in the p-position are very particularly preferred. 
     Possible aromatics of the formula II are, for example, fluorobenzene, o-, m- and p-difluorobenzene, o-m- and p-chlorofluorobenzene, o-, m- and p-bromofluorobenzene, o-, m- and p-fluoroiodobenzene, o-, m- and p-fluorotoluene, o- and p-fluorobiphenyl, o-, m- and p-trifluoromethyl-fluorobenzene, chlorobenzene, o-, m- and p-dichlorobenzene, o-, m- and p-bromochlorobenzene, o-, m- and p-chloroiodobenzene, 4-chlorobiphenyl, o-, m- and p-chlorotoluene, o-, m- and p-chlorotrifluoromethylbenzene, bromobenzene, o-, m- and p-dibromobenzene, o-, m- and p-bromoiodobenzene, o-, m- and p-bromotoluene, o-, m- and p-bromobiphenyl, o-, m- and p-bromobenzotrifluoride, iodobenzene, o- and p-diiodobenzene, o-, m- and p-iodotoluene and 3-iodotrifluoromethylbenzene. Bromobenzene is preferred and fluorobenzene and chlorobenzene are very particularly preferred. If R is different from hydrogen in the compounds RC 6  H 4  Hal, R is preferably halogen. 
     In the bis(acid halides) III Y is preferably CO. Z is, for example, the radical C 6  H 4  -E-C 6  H 4  with E=0, (CG 2 ) m , CO, S, SO or SO 2 , where G is hydrogen, methyl, fluorine or trifluoromethyl and m is an integer from 0 to 4. If m is 0, the two phenylene radicals are thus bonded to one another by a single bond. 
     Examples of bis(acid halides) which may be mentioned are: phosgene, difluorophosgene, sulfuryl chloride, sulfuryl fluoride, terephthaloyl dichloride, isophthaloyl dichloride, 1,4- and 2,6-naphthalenedicarbonyl dichloride, 1,5-anthracenedicarbonyl dichloride, 4,4&#39;-biphenyldicarbonyl dichloride,bis-(4,4&#39;-chlorocarbonylphenyl)-methane,2,2-bis-(4,4&#39;-chlorocarbonylphenyl)-propane, hexafluoro-2,2-bis-(4,4&#39;-chlorocarbonylphenyl)-propane, di-(4,4&#39;-chlorocarbonylphenyl) ketone, di-(4,4&#39;-chlorocarbonylphenyl) ether, di-(4,4&#39;-chlorocarbonylphenyl) sulfide, di-(4,4&#39;-chlorocarbonylphenyl) sulfoxide, di-(,4,4&#39;-chlorocarbonylphenyl) sulfone, pyridine-2,5-dicarbonyl dichloride, 2,5-thiophenedicarbonyl dichloride, 1,3- and 1,4-benzenedisulfonyl dichloride, 4,4&#39;-biphenyldisulfonyl dichloride, 2,2-bis-(4,4&#39;-chlorosulfonylphenyl)-propane, bexafluoro-2,2-bis-(4,4&#39;-chlorosulfonylphenyl)-propane, di-(4,4&#39;-chlorosulfonylphenyl) ether, di-0(4,4&#39;-chlorosulfonylphenyl) sulfide, di-(4,4&#39;-chlorosulfonylphenyl) sulfoxide, di-(4,4&#39;-chlorosulfonylphenyl) sulfone and di-(4,4&#39;-chlorosulfonylphenyl) ketone. Phosgene, sulfuryl chloride, terephthaloyl dichloride, di-(4,4&#39;-chlorocarbonylphenyl) ketone, 4,4&#39;-biphenyldicarbonyl dichloride, di-(4,4&#39;-chlorocarbonylphenyl) ether, di-(4,4-chlorocarbonylphenyl) sulfide and di-(4,4&#39;-chlorocarbonylphenyl) sulfone are preferred. 
     The compounds of the formula II and the formula III mentioned as examples are either known or can be prepared by analogous processes. 
     The end products obtained of the formula I are for example 4,4&#39;-difluorobenzophenone, 4,4&#39;-dichlorobenzophenone, bis-(4-fluorophenyl) sulfone, bis-(4-chlorophenyl)sulfone, 1,4-bis-(4-fluorobenzoyl)-benzene, 1,4-bis-(4-chlorobenzoyl)-benzene, 4,4&#39;-bis-(4-fluorobenzoyl)-diphenyl ether, 4,4&#39;-bis-(4-fluorobenzoyl)biphenyl, 4,4&#39;-bis-(4-fluorobenzoyl)-diphenyl sulfide and 4,4&#39;-bis-(4-fluorobenzoyl)-diphenyl sulfone. 
     2 to 10, preferably 2 to 3, moles of II are in general employed per mole of bis(acid halide) III in the process according to the invention. Furthermore, 0.1 or 1 to 100 moles, preferably 10 to 50 moles, and in particular 20 to 30 moles of hydrogen fluoride are in general employed per mole of bis(acid halide) III. Amounts of less than 1 mole of hydrogen fluoride are only used if starting from a bis(acid fluoride). In this case, the use of larger amounts of hydrogen fluoride is uncritical for the reaction. It is then advantageous to use only comparatively small amounts of hydrogen fluoride, usually not more than 30 and, in particular, 1 to 5 moles. 
     The process according to the invention is in generally carried out at temperatures from -80° to +200° C., preferably from 0° to +50° C. The boron trifluoride is in general used in an amount of at least 2 moles per mole of bis(acid halide) III, for example from 2.5 to 10 moles. The process can be carried out at atmospheric pressure, but working at higher pressure, in particular at a total pressure of 5 to 70 bar, is preferred. If the process is carried out at elevated pressure, the process can, for example, be carried out in a stainless steel autoclave which is optionally lined with a resistant material such as polytetrafluoroethylene, the starting materials II and III being initially introduced and hydrogen fluoride being pumped in, for example in the molar amounts given above, based on the bis(acid halide) III. 
     It is often expedient to start from those bis(acid halides) in which Hal is fluorine. These compounds do not need to be employed as such, but in an advantageous embodiment are prepared in situ by reacting those compounds III in which Hal is chlorine, bromine or iodine with at least the equivalent amount of hydrogen fluoride. This transhalogenation may be carried out, for example, at -20° to +200° C., preferably at 40 ° to 80° C., in particular at 50° to 70° C., for example by keeping the mixture in intimate contact for 2 to 24 hours by stirring or shaking. The resulting hydrogen halide may be evaporated off, for example at 0° to 10° C., if desired via a column. Boron trifluoride is then introduced under pressure, usually at a temperature up to 50° C., and the crude product which still contains hydrogen fluoride is reacted under the abovementioned conditions. 
     In another embodiment, the compounds II and III may also be initially introduced in hydrogen fluoride. Boron trifluoride is then introduced under a pressure of 5 to 70 bar at the abovementioned temperatures and the reaction is carried out to give the compounds I. 
     Working-up is carried out by evaporating the boron trifluoride and the hydrogen fluoride. They may be reused. The crude product of the formula I obtained in this way may be purified by crystallization, if appropriate in the presence of a base such as MgO, Na 2  CO 3  or K 2  CO 3 , washing or distillation or a combination of these measures. 
     The advantage of the process according to the invention is that the compounds II and III can be employed in equimolar amounts and the hydrogen fluoride and the boron trifluoride can be recovered without difficulty. There is thus no effluent in this process, nor are there any emissions of pollutants, which is of great importance for a modern process. 
     In addition, in contrast to the known process, which is carried out with aluminum chloride, a homogeneous reaction mixture is reacted according to the invention, so that no mixing or separation problems occur. 
     The bis-(4-halobenzoyl) compounds obtained by the process according to the invention, of which 1,4-bis-(4-fluorobenzoyl)-benzene and 1,4-bis-(4-chlorobenzoyl)-benzene are preferred, are useful monomers for chemically resistant plastics which are still resistant even at high temperatures. They may be used directly, without further purification, for polycondensations after dissolving in suitable solvents, if appropriate with the addition of solid bases, preferably Na 2  CO 3 , K 2  CO 3  or MgO, and subsequent filtration if necessary, for example with hydroquinone to give polyether ketones. 
    
    
     The invention is illustrated by the examples below, where m.p. means melting point, h means hours and BFB means 1,4-bis-(4-fluorobenzoyl)-benzene. 
     EXAMPLES 
     1. 20.3 g of terephthaloyl dichloride, 19.2 g of fluorobenzene and 50 g of hydrogen fluoride were initially introduced into a 250 ml stainless steel autoclave and boron trifluoride was introduced under pressure at 10 bar. The autoclave was shaken for 16.5 h at room temperature. Working-up was carried out by initially evaporating the volatile components at room temperature and then at 60° to 100° C. and recrystallizing the residue from chlorobenzene in the presence of sodium carbonate. 19.76 g of 1,4-bis-(4-fluorobenzoyl)-benzene were obtained in the form of colorless crystals of m.p. 221° C. Examination by means of high pressure liquid chromatography (HPLC) gave a degree of purity of 99.5%. 
     2. As in Example 1, 20.3 g of terephthaloyl dichloride, 21.1 g of fluorobenzene and 50 g of hydrogenfluoride were reacted for 18 h at 50° C. at a BF 3  pressure of 11.5 bar. After working-up, 20 g of BFB were obtained (HPLC purity 99%). 
     3. The same batch as in Example 2 was reacted for 47 h at room temperature. 24.5 g of BFB were obtained (HPLC purity 99.5%). 
     4. 20.3 g of terephthaloyl dichloride, 21.1 g of fluorobenzene and 50 g of hydrogen fluoride were initially introduced at 0° to 10° C. into a 250 ml autoclave made of stainless steel and the mixture was shaken for 3 h at 50° C. It was then cooled to 0° C., the resulting HCl pressure was released and BF 3  was introduced at a pressure of 10 bar. The mixture was shaken for 15 h at room temperature and 25.6 g of BFB were obtained by working-up as in Example 1 (HPLC purity 99.5%). 
     5. Example 4 was repeated with the modification that the mixture was shaken for 16.5 h at room temperature at a BF 3  pressure of 64 bar. The yield of BFB was 28.8 g (HPLC purity 99.5%). 
     COMPARISON EXPERIMENT 1 (WITHOUT BF 3 ) 
     20.3 g of terephthaloyl dichloride, 21.1 g of fluorobenzene and 50 g of hydrogen fluoride were shaken for 24 h at room temperature in a 250 ml stainless steel autoclave. After working-up according to Example 1, no BFB was obtained. 
     COMPARISON EXPERIMENT 2 (WITHOUT HF) 
     20.3 g of terephthaloyl dichloride and 28.8 g of fluorobenzene were initially introduced into a 250 ml stainless steel autoclave, boron trifluoride was introduced at a pressure of 60 bar and the mixture was shaken for 26 h at room temperature. After working-up according to Example 1, 2.2 g of BFB were obtained. 
     6. 34 g (0.2 mol) of terephthaloyl difluoride, 115 g (1.2 mol) of fluorobenzene and 4 g (0.2 mol) of anhydrous hydrogen fluoride were initially introduced into a 250 ml stainless steel shaking autoclave. A total of 39 g (0.58 mol) of boron trifluoride was introduced under pressure and the mixture was shaken for 24 h at 20° to 40° C. The autoclave was depressurized and the reaction product was worked up as described in Example 1.54 g (83.8%) of BFB were obtained (HPLC purity 99%). 
     7. 17 g (0.1 mol) of terephthaloyl difluoride, 57.5 g (0.6 mol) of fluorobenzene and 5 g (0.25 mol) of anhydrous hydrogen fluoride were initially introduced into a 250 ml stainless steel shaking autoclave. The reaction was carried out in the same way as in Example 6 and 26.5 g (82.4%) of BFB (HPLC purity 99%) were obtained.