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Patented Aug. 24, 1948 2, 447,717 UNITED STATES PATENT OFFICE 2,447.717 FLUORINATION OF ORGANIC COMPOUNDS Joseph H. Sim ons, S tate College, Fa., assignor to M innesota M ining & M anufacturing Company, St. Paul, M inn., a corporation of Delaware No Drawing. A pplication December 7,1948, Serial No. 714,918 8 Claim s. (CL 260--539) This application is a continuation-in-part of which may be evolved in the fluorination process, copending application Ser. No. 562,570, filed without the vehicle being rendered acidic, owing November 8, 1944, now abandoned. to the basic nature of pyridine. I t has been found This invention relates to a method of directly advantageous to maintain a basic vehicle as such fluorinating organic compounds by reaction with . vehicle is more favorable to the desired fluo elementary fluorine in a liquid solvent diluent. rination reaction In many cases. Pyridine is an The fluorination of organic compounds in an excellent solvent, a large number of organic com inert liquid vehicle by means of elementary pounds being highly soluble therein. fluorine has previously been proposed. See the Pyridine can react with fluorine to form a Calcott and Benning Patent No. 2,013,030, issued 20 fluorinated pyridine, such as fluoropyrldine Sept. 3, 1935, which mentions anhydrous liquid (wherein a fluorine atom replaces a hydrogen hydrogen fluoride, fluorsulfonic acid, and fluo- atom and is directly bonded to a carbon atom by rinated hydrocarbons as suitable. These are a covalent bond), as distinguished from the ad representative of acidic and neutral liquids. ditive complex previously mentioned. However, I have found that pyridine, which is readily 25 the fluorinated pyridine thus produced is itself a available at a reasonable cost, has marked ad highly stable and insert solvent diluent material. vantages over the acidic and neutral liquids pre The fluorinated pyridine is basic, forms addition viously proposed. Pyridine is basic. complexes with fluorine, and functions similarly Elementary fluorine is the most chemically to pyridine. Hence the effect of fluorination of active element known. Fluorination is somewhat 25 the pyridine solvent Is not to decrease the similar to oxidation, but is an even stronger re molecular ratio of the Inert fluorine-transferring action. Fluorine reacts violently with most solvent relative to the organic solute being fluo organic compounds, even at reduced tempera rinated. but merely to consume some of the tures, causing a destructive decomposition or fluorine, making it unavailable for fluorination degradation, unless the reaction is controlled. 25 of the organic solute. Obviously a liquid cannot be used as a diluent At reduced temperatures, below 0" C., the rate vehicle, in which the organic compound to be of fluorination of the pyridine solvent diluent fluorinated is dissolved, if the vehicle is itself employed in the process is quite slow, so that for unfavorably reactive to the elementary fluorine. practical purposes the diluent remains essentially It would naturally be supposed th at pyridine 30 a pyridine solvent and can be recovered as such would react violently with fluorine, as does with little loss. benzene. Even at higher temperatures, the rate of fluo I have discovered, contrary to expectation, that rination of the pyridine will be slow when the pyridine has little reactivity to fluorine at tem solvent contains an organic compound solute peratures below 0" C. and has other properties 35 which is readily fluorinated. In such case the which make it highly suitable for use as a fluo- tendency is for the fluorine atoms to fluorinate rlnatioH diluent. the solute as against fluorinating the pyridine. When elementary fluorine Is introduced into Since fluorinated pyridine is itself an effective pyridine at reduced temperatures, a molecular inert solvent diluent, it can be recovered and complex is formed, wherein fluorine atoms are 40 used as the diluent in performing the process- loosely held by the pyridine molecules, and this upon other occasions. The Invention embraces complex can act as a fluorinating agent. The the use of fluorinated pyridine as an inert solvent complex transfers fluorine to the organic com diluent, and in some cases it may be desired to pound solute so as to cause fluorination thereof employ it exclusively, without making use of in a moderate and controlled fashion which 45 pyridine. avoids the violent and destructive or degradative Thus the invention Is not restricted to the use action characteristic of direct fluorination. The of simple pyridine, but includes pyridine deriva effect is quite different from th at resulting when tives which likewise form addition complexes fluorine is dissolved as a simple solution in an with fluorine but are relatively Insert to fluorina- inert solvent vehicle which does not form the 50 tlon (1. e. valence bonding of fluorine) when complex. Moreover, the pyridine absorbs rela employed as solvent diluents for fluorinatable tively much larger quantities of fluorine than do organic compound solutes. A further example is solvents which do not form such a complex. A methyl pyridine. Other compounds containing further advantage of pyridine Is that it Is capable the pyridine ring may be employed as equivalents, of absorbing small amounts of hydrogen fluoride 55 such as quinoline; and other azlne ring comt- E x h ib it 1005 State of Minnesota v. 3M Co., Court File No. 27-CV-10-28862 - 1005.0001 STATE 07524645 2,447,717 pounds containing more than one nitrogen atom black slurry was ether-extracted. The ether so in the nucleus, such as dlazlnes. lution was separated, washed with water, dried The reaction vessel may be of copper or silver over solid NaOH, and fractionated through a construction to render it corrosion-resistant, pro small five-plate column. Cuts boiling from 80 vided with a cooling jacket for temperature con 86 C,, totalling 23 grams, were refractionated trol, and with mechanical stirring means. The through a small metal-packed column having an fluorine gas stream preferably enters Into the estimated 30 theoretical plates. Decalln was vessel below the liquid surface and In the form used to back the distillation. The following frac of small well-dispersed bubbles. Inlet and out tions were obtained: let ports may be provided for continuous opera 10 tion. Where the reaction product Is removable as a vapor, further additions of the organic re actant may be made from time to time, or con Cut B. P. Weight Refractive (0.) (grams) Index tinuously, without further addition of solvent diluent. A reflux condenser may be provided. The fluorine gas may be diluted with an inert gas, such as nitrogen, In order to retard the re 1......................................... ................ 2................. ..................................... 3......................................... ,, . 4................................................ 5............................................. 68-79 7980 8082-83 0.2 810.6 13.6 832.6 2.0 1.4950 1.4961 1.4921 1.4753 action and permit of better control of heat In the reaction vessel. Cut 5 had a molecular weight (Dumas gas den- A catalyst may be employed but, in general, 20 sity method) of 95.6. It was separated by low there is no need for catalytic assistance in view of temperature filtration through a sintered glass the fluorination activity. disk, the lower melting fluorobenzene (M. P. The reaction of pyridine and fluorine is illus --42 C.) being thus separated from the higher trated by an experiment In which pyridine dis melting benzene (M. P. 5 C.). In order to ob- solved in 2-fluoropyridine was treated at 0 C. for 25 tain a pure sample of fluorobenzene, only a 0.2 four hours with fluorine gas diluted with nitro gram sample was collected in the first fraction. gen, resulting in the conversion of 40% of the This sample had a melting range of --48 to --42 pyridine into fluoropyridine. In this case the C.; a refractive index of 1.4698; and a fluorine fluoropyrldlne served as an inert solvent diluent. content of 18.6% as determined by Parr bomb fu- The absence of a different fluorlnatable organic 30 sion and titration of the resultant fluoride ion solute to preferentially react with fluorine ex content with standard thorium nitrate. The the plains why the pyridine was fluorinated to this oretical value for fluorobenzene (CeHsF) is extent. When such a fluorinatable organic so 19.7%: and the reported refractive index value is lute is present, the rate of fluorination of pyridine 1.4684. is made much slower, so that It is possible for the 35 The residues from the first fractionation were pyridine to behave as a highly Inert (non-reac- distilled in a simple distilling flask, and the fol tlve) diluent. lowing cuts were obtained: The following examples further serve to illus trate the Invention. AH parts are by weight, ex if is cept as noted. 40 C ut B .P .(C .) Example 1 1............................................ Up to 118 3 A reaction vessel was charged with 19 parts of toluene dissolved In 79 parts of pyridine. Fluo a................................................................. 8................................................................. 4................................................................. 118-123 123-127 127-150 4 1. 5 0.5 rine gas diluted with nitrogen (1:25 ratio) was 45 - passed through the solution, the temperature be ing about --20" C. After purification and distil lation of the resulting reaction mixture, two flu orinated toluenes were obtained. One distilled at 100-110 C. at a pressure of 120 mm., was more 50 A black heavy residue remained as a pot residue. In this experiment only a small amount of flu orinated pyridine was formed, demonstrating the preferential fluorination of the benzene. dense than water, and contained by analysis Example 4 ' 46.4% fluorine. The other boiled at 93-103 C. at atmospheric pressure and contained 18-20% flu orine; Example 2 65 A glass reaction vessel was filled with 65 grams of glacial acetic acid and 169 grams of dry frac tionated pyridine. A dry, oxygen-free, fluorine and nitrogen mixture (1:10 ratio) was introduced Fluorine diluted with nitrogen was passed through a copper tube at the rate of 0.1 mol of through a solution of 30 parts acetophenone in 79 fluorine per hour, for a total of 11.5 hours. The parts pyridine at a temperature of --25 to --40 C., reaction vessel was kept at --10 to --25 C. The resulting in fluorination of the acetophenone and reaction proceeded smoothly, with the evolution the production of difluoroacetophenone. 60 of white fumes. Example 3 Products containing combined fluorine were obtained. I t appears probable that some fluoro- A solution of 90 cc. of dry, refractionated ben acetic acid was produced. zene (B. P. 80 C.) in 160 cc. of dry, refractionated pyridine (B. P. 115-116 C.), was treated with 05 Exam ple 5 0.75 mol of fluorine, which was diluted with nitro Fluorine gas was passed Into a 10% solution gen in a 1:10 ratio. The nitrogen had been of benzene In 2-fiuoropyridine, at a temperature treated with alkaline pyrogallol to remove any of 0 C. A solid reaction product was obtained oxygen and then dried with phosphorous pent- which, after removal of fluoropyridine, was found oxide. The reaction temperature was --15 C. 70 to contain approximately 20% fluorine by weight. The reaction proceeded smoothly. White fumes were evolved and the solution became dark and Example 6 somewhat viscous. A10% solution of butyric acid In 2-fluoropyri The reaction products were poured onto ice- dine was treated with fluorine at 0 C. Products cold dilute hydrochloric acid and the resulting 75 containing combined fluorine were obtained, and 1005.0002 STATE 07524646 8,447,717 56 it appears probable that some fiuorobutyrlc acid substantially inert to the fluorine but forms a was produced. molecular complex therewith acting as a fluori- Example 7 . natlng agent for the dissolved organic compound Acetic acid dissolved in 2-fluoropyridine was treated with fluorine at 0 C. The reaction pro ceeded smoothly, without explosion. The prod ucts were not analyzed. Having described various embodiments of the invention, lor purposes of illustration rather than limitation, what I claim is as follows: 1. In a process of producing organic fluorine compounds, the steps which comprise reacting fluorine with a fluorinatable organic compound solute in a substantially inert liciuid solvent dilu ent of the class consisting of pyridine and fluorinated pyridine, and recovering a fluorinated product of said solute. 2. A method according to claim 1, wherein a reduced temperature is maintained not exceeding 5 10 1# to produce fluorination thereof in a smooth nonviolent manner, and recovering a fluorinated product of said organic compound, B. In a process of producing organic fluorine compounds, Introducing elementary fluorine into a liquid mixture essentially comprising fluoropyri- dine and an added organic compound solute which is highly reactive to fluorine, the mixture being maintained at a temperature such that the fluoropyridine serves as a liquid solvent dilu ent which is substantially inert to the fluorine but forms a molecular complex therewith acting as a fluorinating agent for the dissolved organic compound to produce fluorination thereof In a smooth non-vlolent manner, and recovering a fluorinated product of said organic compound. about 0" C. 20 JOSEPH H. SIMONS. 3. A method according to claim 1, wherein said organic compound is a hydrocarbon. REFERENCES CITED 4. A method according to claim 1, wherein said organic compound is an aromatic hydrocarbon. 5. A method according to claim 1, wherein said 25 The following references file of this patent: are of record In the organic compound is an acid. S. A method according to claim 1, wherein said TTOTTED STATES PATENTS organic compound is acetic acid. Number Name Date 7. In a process of producing organic fluorine 30 2,013,030 C alcottetal____ ___ Sept. 3,1035 compounds, introducing elementary fluorine into 2,013,035 Daudt et al_________ Sept. 3,1935 a liquid mixture essentially comprising pyridine and an added organic compound solute which FOREION PATENTS is highly reactive to fluorine, the mixture being maintained at a temperature such that the pyri Number Country Date dine serves as a liquid solvent diluent which is 786,123 F rance____________ June 3, 1935 1005.0003 STATE 07524647