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WILLIAM T . MILLER, JR.,
JOHN
D. CALPEE AND LUCIUS A. BIGELOW
VOl. 59
by McTaggart and by Lenard and his students. from 0.0001 N up to 3, 1 and 0.1 N , respectively, Since the cohesion, and therefore also the surface and of sucrose solutions from 0.0002 molar up to tension, of water is probably largely due to the 0.005 molar. electric forces between the dipoles, a disturbance 3. These three salts all increase the surface of the normal electric distribution may cause a tension of water from 0.01 N up to the highest diminution of the surface tension. concentration studied and give surface tensionAs the solution becomes more concentrated concentration curves which are typical of strong (about 0.01 N or above), the mutual attraction electrolytes that are capillary inactive and negabetween ions of opposite polarity becomes tively adsorbed in the surface layer. stronger than the forces between the ions and the 4. At extreme dilutions (below about 0.006 N ) water molecules and causes negative adsorption all three salts cause a decrease in surface tension and an increase in surface tension in the manner and are, therefore, positively adsorbed in the surdiscussed by Onsager and Samaras. We may face layer at concentrations below that giving the conclude, therefore, that the treatment of Onsager minimum (about 0.001 N ) of the surface tension. and Samaras is over simplified and thus fails to 5. Sucrose gives a linear surface tensiongive a complete and accurate result. concentration curve with no change in the sign of the slope a t extreme dilutions. Summary 6. The data are not in accord with the On1. A modification of the capillary rise method s a g e r a a m a s equation for the surface tension of measuring the surface tension of solutions rela- as a function of the concentration. tive to that of the pure solvent, which makes it a 7. The influence which causes diminished differential method and substantially improves surface tension and positive adsorption at exthe accuracy oi the results, is described. treme dilution is ionic in character and probably 2 . The relative surface tension of aqueous due to an interaction between the ions and polarsolutions of potassium chloride, potassium sulfate, ized water molecules. and cesium nitrates has been determined a t 25' CAMBRIDGE, MASS. RECEIVED JULY 29, 1936
[CONTRIBUTION FROM THE CHEMICAL LABORATORY OF DUKE UNIVERSITY]
The Action of Elementary Fluorine upon Organic Compounds. 111. The Vapor Phase Fluorination of Hexachloroethane BY WILLIAM T. MILLER, JR., JOHN D. CALFRE AND LUCIUS A. BIGELOW Previous papers in this series' have described the fluorination of certain organic compounds dissolved in carbon tetrachloride, using, however, an open type of generator as the source of the halogen. This earlier procedure had two disadvantages, since the fluorine produced was contaminated with other gases, and also reacted to a considerable extent with the solvent. More recently, we have designed a new closed generator2 capable of delivering fluorine 94-99% pure, and in addition have considered it desirable to avoid the use of solvents altogether. The present paper describes the vapor phase fluorination of hexachloroethane over a copper gauze catalyst. It is probable, of course, that the reaction took place (1) Tnxs JOURNAL, 66,4614 (1933); 6 4 2 7 7 8 (1834),
(2) Miller and Bigolow, ibld., 64,1886 (1888).
at the surface of the metal, which acquired a thin coating of copper salts during the process, and cupric fluoride may have been the immediate fluorinating agent. However, the change did not occur rapidly a t ordinary temperatures, and the gauze was not greatly attacked over a considerable period of time, even when heated. So far as the writers are aware, no similar, direct, vapor phase fluorination of an organic compound containing more than one carbon atom has as yet been reported, in which definite chemical individuals have been formed. The procedure employed in this fluorination was exceedingly simple. The sample was placed in a horizontal tube, between two copper gauze rolls, suitably heated. The fluorine, diluted with nitrogen, was introduced at the center of one of
Jan., 1937
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these rolls, in a manner somewhat similar to that tinuous reaction took place, the fluorine being aldescribed by Fredenhagen and C a d e n b a ~ h . ~ways in excess. The products were condensed as Under appropriate conditions, a perfectly quiet, a mixture of liquid and solid in a trap at about continuous reaction occurred, and the products -4OO. On warming to room temperature there were condensed a t reduced temperatures. After remained a clear liquid, which was formed a t the purification and rectification in a Podbielniak rate of about 1.6 g. per hour. For each 10 g. of still, the main product, which was sym-difluoro- hexachloroethane utilized, approximately 7.4 g. of tetrachloroethane, boiled a t 92O, and melted a t this liquid was produced. The crude material 24-25 O , corresponding closely to the values pre- was dissolved in ether, washed with 5% sodium viously reported by Locke, Bride and Henne,4 carbonate solution and dried over calcium chlowho obtained the compound by another method. ride, during which process a considerable portion The yield of the pure haloethane was approxi- of it dissolved. The ether solution was then mately 20%. A further study of this and similar fractionated directly in a Podbielniak still. The pure product, b. p. 9 2 O , m. p. 24-25', was obreactions is contemplated. tained in approximately 20% yield. According Experimental to Locke, Bride and Henne4 sym-difluorotetraThe fluorination was carried out in a Pyrex chloroethane boils at 92.8' and melts at 24.7'. glass tube, diameter 2.8 cm., length 75 cm. The A d , Calcd. for CtFnC&: F, 18.6; C1,69.6;mol. wt., gas was introduced through a 6.3-mm. copper 204. Found: F, 18.5,18.7; C1, 69.3,69.5; mol. wt.,209, tube, closed a t the end, but perforated irregularly 210. along the last 4 cm. of its length. The perforaThe fluorine analyses were made by the Willard tions were surrounded by a tight roll of clean 20- and Winter method, after decomposing the sammesh copper gauze, 6 cm. in length, which fitted ple in a Parr bomb. snugly into the glass tube. The charge was When tetrachloroethylene, b. p. 119', was placed in the 10-cm. space immediately following fluorinated in a similar manner, with both gauzes the gauze, and the total distance occupied by both a t 130°, and the haloethylene in excess, sym-diof these was surrounded, on the outside, by a slid- fluorotetrachloroethane, boiling a t 92O, was also ing metal air bath. Beyond the charge, the re- produced, in about 20% yield, and further identiaction tube was filled for a length of 25 cm. with fied by means of a mixed melting point. Conanother roll of gauze, surrounded by a second, siderable substitution took place a t the same independent air-bath. In this very simple set up, time, however. In this case, the sample was inconnections were made with ordinary stoppers, troduced by passing nitrogen through the refluxwrapped with copper foil and painted with Ceresin ing liquid, heated in a bath a t 135'. wax. summary In operation, the tube was first swept out with nitrogen, and the second gauze heated to 160'. Hexachloroethane has been fluorinated diThen the fluorine, diluted with nitrogen in the rectly, in the vapor phase over a copper gauze ratio of 1:1.6, was passed in a t a rate correspond- catalyst. A 20% yield of pure sym-difluorotetraing to a current of 3.8 amp. through the generator chloroethane was obtained. Tetrachloroethylene, (roughly 1.5 liters per hour). Finally the first under similar conditions, yielded the same prodgauze was heated gradually to 125', when a con- uct. (3) Fredenhagen and Cadenhach, Bn.,61,928 (1934). DURHAM, N . C. RECEIVED NOVEMBER 7,1936 (4) Locke, Bride and Henne, THISJOURNAL, 66, 1726 (1934).
