ACTION OF FLUORINE ON ORGANIC COMPOUNDS1 BY BURR HUMISTON
The action of fluorine on organic compounds is usually very violent resulting in the total disintegration of the compound in question. In the case of hydrocarbons, hydrofluoric acid and carbon fluorides are formed. Saturated hydrocarbons such as paraffin and “Nujol” when exposed to undiluted fluorine burn with incandescence, giving free carbon and carbon fluorides as the reaction products. Many experiments were tried in this laboratory on the preparation of organic fluorides, the first work being on carbon fluorides. Carbon and graphite are attacked by fluorine if in a granular or powdered condition. Moissan2 gives the action of fluorine on lamp-black, charcoal, graphite, and diamond. He found that lamp-black and charcoal are easily attacked; but pieces of graphite must be brought almost to redness before the reaction sets in; while diamond does not lose weight when heated to redness in a Bunsen burner and then exposed to fluorine. He obtained a mixture of carbon fluorides in every case. Fluorine was passed over approximately twenty grams of “filtchar” in a copper tube and the gases led into a test tube by solid carbon dioxide and ether. Although cooled to -80 the tube containing the charcoal was at room temperature, the reaction started as soon as the fluorine was passed in; and the temperature rose quickly. After about six hours fluorine came through the system and it was supposed that the carbon was entirely converted to fluoride. On opening the reaction tube it was found that a large portion of the carbon was covered with a gray dust which appeared to be mineral matter. This materially slowed down the action of the fluorine. Only ten grams of carbon fluoride were condensed whereas if all the fluorine which acted on the charcoal had gone to carbon 1 2
Published by permission of the Director of Chemical Warfare Service. Comptes rendus, 110, 2 7 6 (1890).
a
Action of Fluorine on Organic Compounds
57 3
tetrafluoride, approximately 35 grams would have been formed. The product condensed was a mixture of CF4 which boils No attempt was at -15' and C2F4 which boils at -32'. made to condense the compound that distills below -Soo. Since the fluorides of carbon boil at so low a temperature it was thought that more satisfactory results could be obtained with selenium. Lebeaul found that SeF4 boils at 100'. Prideaux2 found a low-boiling selenium fluoride to which he assigns the formula SeF6. Forty grams of selenium in small granules were placed in a reaction tube and fluorine passed in. The receiver was kept cold with ice and a secondary condenser cooled with solid carbon dioxide and ether placed next to it, to remove the last traces of selenium tetrafluoride. Fluorine was passed into the tube until all the selenium had been acted on. This was ascertained by the presence of fluorine at the mouth of the last receiver. But six grams of product were found in the condenser cooled with ice while theory calls for 97 gm. SeF6or 78 gm. SeF4. No appreciable quantity was found in the condenser cooled with COz and ether. As was the case with carbon most of the product could not be condensed above -soo. If acetone in an open platinum dish be exposed to fluorine, the liquid quickly takes fire. In the first experiment fluorine and air saturated with acetone were brought together in a small copper tube which led to a test tube cooled in solid COa and ether. Fluorine was noticed at all times at the mouth of the test tube used as condenser and to reduce this excess a larger percentage of acetone was sent in. An explosion resulted which wrecked the apparatus. In the next experiment fluorine diluted with carbon dioxide was bubbled through acetone at room temperature. The dilution of fluorine was such that small explosions and burning did not take place at the mouth of the fluorine delivery tube. Fluorine appeared to dissolve in the liquid Comptes rendus, 144,1042 (1907). Jour. Chem. SOC.,84, 316 (1906).
5 74
'
Burr. Humiston
and as the reaction proceeded, the liquid went from a deep yellow to a brown or black. Some low-boiling carbon fluoride The was always found in the condenser cooled to -80'. final product was distilled under reduced pressure. After distilling off the excess acetone, only a charred residue remained. Further experiments were carried out keeping the acetone cooled with ice and using nitrogen in place of COz as a diluent. The same results were obtained as in the previous experiment. An attempt was next made to bring the vapors of acetone and fluorine together in fluorspar sand at 100'. Charring again resulted. If fluorine was passed for a long time a viscous, tarry product was obtained. It was observed that the glass apparatus was attacked showing that some hydrofluoric acid had been formed. Since the results with acetone were so unsatisfactory, it was decided to use a chlorinated compound. Twenty-five grams of chloroform were placed in the same apparatus and fluorine passed at a rate of 2 grams per hour for 3 hours. A yellow liquid collected in the first flask. This appeared to be a mixture of chloroform, chlorine and phosgene. The liquid which condensed in the condenser at -80' boiled It was a mixture of phosgene, chloroform and a t -65'. probably carbon fluoride. An experiment similar to the above was carried out a t a lower temperature. The reaction tube was cooled with ice and the chloroform was brought in as a vapor by bubbling nitrogen through it at a temperature of 40'. On distilling the product found in the first receiver, a z cc fraction that smelled like chloroform came over below 50'. In the condenser cooled with C02 and ether, 3 cc distilled over between -3' and 25'. This was largely phosgene. One cc distilled from 25' to 50'; the residue was a burnt tarry mass similar to that obtained in the experiments with acetone. If fluorine be bubbled through Nujol at ordinary temperatures the reaction takes place with a brilliant flame and carbon is deposited.
Action of Fluorine o n Organic Compounds
5 75
If fluorine is bubbled through phosgene at six degrees there appears to be no action on the liquid. The vapor above the liquid was tested for the presence of fluorine by bringing an inverted gas jet near the vessel. The gas ignited and a small explosion took place which we assumed to be due to the reaction between phosgene and fluorine in the gaseous phase. This is the first evidence we have had that fluorine and phosgene react, and experiments were begun to study the reaction. The first experiment tried was heating phosgene vapor with a coil of nichrome wire in the presence of fluorine. As the wire was exposed to both chlorine and fluorine at a temperature of approximately zoo ' it was rapidly attacked and disintegrated before either a reaction was detected or products were collected. Phosgene and fluorine were next passed over granulated CaFz heated to zoo', in a glass tube. A product was conWith an excess of fluorine the densed that boiled a t -42'. color of the product was red; with an excess of phosgene it was yellow. On three occasions an explosion took place in the reaction tube or in the condenser wrecking the apparatus. For this reason a copper apparatus was set up and fluorine and phosgene passed as in the glass apparatus. As no provision was made to take care of the chlorine that resulted both from the decomposition of the phosgene and the reaction a mixture was collected which contained a great deal of chlorine. Attempts were made to fractionate the product but with little success. To obviate the difficulty a condenser was put in the line ahead of the condenser that was to receive the pure product; the former condenser being maintained a t -40'. A product was then collected that boiled a t apand had a molecular weight of 66.26. proximately -42' The molecular weight of COF, is 66, and it was thought that this compound was formed. It was analyzed for fluorine and but 9.7570 was found. More of the product was made and a fraction collected that distilled below -52 '. This likewise contained a relatively small amount of fluorine. There is unquestionably a reaction between phosgene and fluorine and i t is probable that some COP2 is formed. The product
5 76
Burr Hunziston
analyzed contained a large amount of chlorine and it is thought that it was a mixture of COFz and chlorine. Carbon monoxide prepared by heating oxalic acid and sulphuric acid was passed through caustic and dried with sulphuric acid. It was then led into a quartz tube along with fluorine and exposed to ultraviolet light. No reaction was noticed nor were any products condensed at -80". Fluorine and carbon monoxide were then passed over Dorsey charcoal a t 35". The charcoal was first heated to 250-300' and allowed to cool while carbon monoxide was passing. Then fluorine and carbon monoxide were passed in together and the product condensed in a test tube at -80". The charcoal became hot in the end where fluorine entered and small explosions could be heard. After running in fluorine at the rate of 3 grams per hour for four hours the condensing tube was examined and a colorless liquid found that boiled at -20'. As much of the carbon was used up there is no question but that it was largely carbon fluorides. Since phosgene is not acted on by fluorine a t low temperatures it suggests itself as a good solvent for diluting other organic substances on which it was desired to test the action of fluorine. The boiling point is so low however that considerable experimental difficulty is involved in its use. It was found that carbon tetrachloride was attacked but slightly a t ordinary temperatures and so could be used more simply than phosgene. Fifty grams of CzC14were mixed with IOO grams of CC14 and fluorine passed into the solution. The mixture which was cooled with an ice bath, was stirred continuously with a mechanical stirrer. The solution was clear for a time but gradually blackened. Charring was rapid in case the solution was allowed to heat up. On distilling the product a considerable quantity of CZCl6was found. The experiment was repeated and the action was watched closely. It was found that chlorine was liberated giving a yellowish tinge to the solution that would disappear on standing. It was further noted that little charring took place at the start but as the
Actiow of Fluorine ow Orgawic Compouwds
577
amount of CzC16increased the charring was quite marked. The action of fluorine on CzC16alone dissolved in CC14 should be tried. The action of fluorine on CZCl4is probably as follows: CZC1, 4F = C2F4 2C12 The liberated chlorine then attacks the CZCl4forming C2C16, czc14 c12 = C2cls while the ethylene tetrafluoride breaks down to carbon tetrafluoride and carbon. C2P4 = C R C It is also possible that the intermediate, instable compound is CzFs but this seems less probable. This point was not determined. The work was done in the Catalytic Laboratory of the Research Division.
+
+
+
+
