Journal of Resea rch 0: the National Bureau of Standards Vol. 62, No. 3, March 1959 Research Paper 2938 Fluorination of Haloaromatic Compounds 1,2 Roland E. Florin, Walter J. Pummer, and Leo A. Wall The reactions of BrF3, CIF 3, and IF5 with CoCI6, C6Bro, CoCI5- CF3, and other halo aro­ matic compounds are described. These reactions are not readily controlled, a nd explosions frequently occurred , particularly when BrF3 and ClF3 were used. D ehalogenation of t he reaction products led to certain aromatic flu orocarbons, for example, CsClF5 and C6CIF.-CF3. Completely fluorinated aromatic compounds were not easily obtained, and t herefore the process is not recommended for t he production of these species. 1. Introduction ducLed with apparent safety, leadin g ultimately to very poor yields of the fluorocarbons but to satis­ Until Lhe recen t disclosure of new methods f01 factory yields of their monochloro derivatives. The preparing hexafluorobenzene [1- 3] 3 the only pub. stages of these syntheses are identified in the follow­ lished syntheses [4,5] of aromatic fluorocarbons were ing summary, in which most formulas represent the conversions of hexachlorobenzene to h exafluoro­ merely typical or rough average composition : 'benzene and of pentachloro-a,a,a .. triHuo],otoluene to octafluorotoluene by an indirect procedure involv­ B rF3 ing addition of bromine trifluoride, exchange fluorina­ C,C I,- C F , C,Br Ol. F ,- C F , Cold tion with an timony pentaHuoride, and dehalogena­ II tion with zinc. Attempts were made to modify the method so as to prepare reactive mono .. and bi-functional dm·iva· C,F ,- O F , C,ChF ,- C F , VI tives, as well as the parent fluorocarbons. For ex III n,mple, it was hoped that the final prod uct. in the C,C IF.- C F , SbF, C6 "B r o.JC I4i? s.s- C F 3 vn followin g scheme would be obtained: IV C,H F .- C F 3 C,B rCld",- C F , V II [ TIrF, Zn \' C,Bro --> C,F . Br, --> C,F . B I'2. C,llC IF ,- C F , IX Previously, a syn thesis of a compound of this Lype .n,nd its conversion to a polyphenyl of low molecular TIr F 3 I3r" , weight was r eported [6] from this laboratory. How C,OI, C,Bro.sC I.., F ,., ever, the synthesis was extremcly laborious. The Cold 20 ~) by weigh t , present work was undertaken to find a shorter path X X I 125°, ex plosion X II to the desired compound , whiclJ it is anhci paLed would lead to the synthesis of thermally stable poly .. 1S bF. mel's. The eompoulld prepared earlier was tetl'a­ C,CI.F, fluoro·l ,4-diiodobenzE'ne [6], and in the present work XIII O,F , it was expected and hoped that the meta and ol'tho C,BrC I. F . Z n, EiOH XVI XIV isomers would also be obtained. C,CIF , C,Br,CIo F , XVII XV 2 . Results and Discussion In trying to repeat this previously described prep a .. BrF3 NaI ration, difficulties were experienced in the later, C. B r. C,B « F , C6Brz.sFu Cold XX high-temperature stages of the bromine trifluoride xv III XIX reaction. The conditions of temperature and concen­ C,13r, F , XXI tration prescribed in the literature led to explosions IF.,170' 1 C,Br,.,F •.• very frequently, and less sever e reaction conditiolls X XII were insufficient for producing the desired degree of C,Br, F , fluorination. It was concluded that the operations de­ XXVUI scribed in the original paper are very close to the margin of safety. Milder fluorinations were con- Zn, EtOH - --- ...., C,If2TIrF, C,II2BrF, C.HBr, F , C ,HB r, F , 1 'I'bis paper is based on wo rk sponsored by tbe Ordnan ce Corps,Department ol the Arlll Y, Washington, D.O. XXIII X X IV X X V XXVI 2 Presented as part of t he Sympos ium all Fluorino Chemistry, Division of In­ dustrial anclE ngi nee ring Chem istry, at tbe 130th M eeting 01 thc American Chem­ Z n, CH ,C ONH 2 ical SOCiety, Atlantic Oity, N.J ., September 1956. - ------>, C,H ,F3 3 Figures in brackets indicate the li terature references at t he end of this paper' X XVII 107 The fluorination of hexabromobenzene proceeded and occasionally by the action of bases on "aromatic" smoothly, but subsequent reactions produced none of bromine [8]. In aliphatic fluorocarbons, the replace­ the desired perfluoroaromatic derivatives, although ment of halogen by hydrogen has also been reported several new compounds were isolated. The scheme by Miller [9]. of synthesis requires that bromine trifluoride react I 2 .1. Fluorinations with Halogen Fluorides only by addition, converting the original - OBI' i The procedures for hexachlorobenzene and pen- I tachloro-a,a,a-trifluorotoluene were much alike groups to saturated 6FBr groups. From the be- throughout and are therefore described together. I The hexachlorobenzene was a commercial product; I havior of the fluorination products, it appears that the pentachloro-a,a ,a-trifluorotoluene was a semi­ the bulk and lability of bromine hinder addition and liquid slush or wet crystalline mass obtained by I exhaustive chlorination of a,a,a-trifluorotoluene [10]. favor replacement, leading to unreactive OF2 groups. The bromine trifluoride was a commercial product, I from several sources, used without purification. I The following scheme accounts for some of the The originally 'described procedure involved the products: slow addition of halocarbon to excess bromine tri­ fluoride, in the cold in several portions, with inter­ Br mittent heating to 100 0 0 after addition of each I portion. Two attempts to repeat the procedure led ' BrFa BrO Br to destructive explosions in the later heating stages. I Br Br [::Q:~:] lieF, [ :: Q:~ ] Some of the associated patent specifications suggest . Br other operating conditions [5]. A limited propor- II XXIX XXX tion of bromine trifluoride could be reacted smoothly with the halocarbon feed by adding the bromine trifluoride slowly to a stirred slurry of the halocarbon Br F F in liquid bromine. Two forms of apparatus were used for different ! BrF, :'D~ NoI F - F batch sizes. For batches of up to 500 g of halo­ B , F Br _ F carbon, the feed slurry was contained in a 500-ml F "-F Br eBrX' nickel beaker in an ice bath, and stirred with a ~~ -hp XIX XXI stirrer. Bromine trifluoride was dripped in from a copper separatory funnel with a brass needle I Zn / Zn valve, in which the packing was replaced by Teflon . C,H,OH it' 1 CH 3C ONH2 and located on the downstream side, while the de­ livery tube was long and offset, to allow safe manip­ J-I H ulation of the valve. Addition of bromine trifluoride F - F usually required about 4 to 6 In per batch. Opera­ tion was usually conducted outside the building I Br F H F F when weather permitted, although in the laboratory eH X' '0I-I ' a hood with good draft was sometimes used. Warm, I XXIII XXVII humid weather was undesirable, as the condensation of water in the mixture led to waste of bromine The hypothetical primary product XXIX contains trifluoride, excess heat, and accelerated corrosion. I "allylic" bromine atoms, easily replaced. In equipment of this size, reaction began energetically 'I' A number of other polyhalogen derivatives of and proceeded relatively smoothly until the addition , benzene were treated with halogen fluorides as well. of 1.6 to 1.8 moles of bromine trifluoride pel' mole ' The products from tetrahalobenzenes resembled of hexachlorobenzene or pentachloro-a,a,a-trifluoro­ those from the related hexahalobenzenes, but the toluene had been completed. After this point, fluorination was less easily managed. It was noticed reaction became very slow or ceased. A slight excess ' that, during the zinc dehalogenation stage, some of bromine trifluoride appeared to remain unreacted hydrogen is introduced into the ring when ethanol after warming to 20 0 to 30 0 C and standing covered , is the solvent; this occurs to a much greater extent overnight. I with acetamide as solvent. The dehalogenation in Large batches (6 kg) of pentachloro-a ,a,a-tri- acetamide of one lot of intermediate, approximately fluorotoluene were fluorinated in a larger apparatus 0 6Br2F 6 (XXI), resulted in a large yield of a tri­ consisting of a welded Monel can of about 4-liter ' fluorobenzene, boiling point 83 0 0, identified by its capacity with widened top to retain foam, a I5-gal ' ultraviolet and mass spectra. The precursor of the ice bath, a I-liter Monel separatory funnel, and a · trifluorobenzene is not clear. Its formation prob­ %-hp stirrer. This reaction vessel was monitored I ably involves the replacement of "aromatic" or "un­ by a thermocouple and automatic recorder. The saturated" bromine by hydrogen. This replacement operator was shielded and remained at a distance, is known to be effected by zinc plus mild acid [7] except for short trips to change valve settings or to . 108 add ice to tbe bath. The course of reaction in this Mixtures eontammg less than 10 to 15 percent equipment was not quite consist.ent with observa­ by weight of bromine triHuoride, heated to 110 ° tions in the smaller system. The temperature to 115 ° 0 for 6 hr, appeared to lose the fluorinating nconl on the chart was zigzagged, fluctuating agent by evaporation, and the analysis and prop­ between + 10 ° and + 80° C. An accumulation of erties were unchanged. :Mixtures containing 20 bromine trifluoride in tbe cold alternated wit.h a percent by weight of bromine triiluoride, h eated to relatively rapid reaction (and temperature rise) 120 ° to 130° 0 , appeared inert until a sudden ex­ which temporarily exhausted the bromine trifluoride plosive reaction occurred, vaporizing and spattering and thus allowed the mixture to cool.