FLUORINE CHEMISTRY E. T. McBee PLRDUE UhIVERSITI A\D PLRDUE RESEARCH FOIT\DATIO\,
L&F4YETTE, I h D .
P
RIOR to Korld 1I-m I1 there IT as gioning interest in fluoing of electrolytic cells for the production of fluorine. Fluorine rine chemistry and, because of numerous possible applicais difficult'andexpensive to transport because of its lo^ critical tions in the war effort, research and development in this field temperature of -129" C. ( I ) and because of its corimive nere greatly intensified during the past five years. The Symproperties. posium on Fluorine Chemistry, which made up a large portion Prior to the Manhattan District development, preparation of the program of the Division of Industrial and Engineering and isolation of fluorocarbons had not progressed beyond the Chemistry a t the 110th AIeeting of the AMERICAN CHEMICAL laboratory stage. XniY they have been made commercially on SOCIETY in Chicago, was the formal announcement of the a relatively large scale. and the technology has advanced to major share of the results of this research and development. such a n extent that' many fluorocarbons may be produced on The work reported at this symposium was sponsored by sevany desired scale. Although most fluorocarbons cannot lie eial branches of the armed services as ne11 as by private made cheaply by present methods, they should find wide apgroups and individuals. The largest share of the papers replication in industry because of their nonflammability and essulted from iesearch initiated by the Office of Scientific Ret'reme stability to heat and chemical reagents. For example, search and Development and later sponsored by the Manhatit should now be possible t,o develop new types of engines to optan District, United States Army Corps of Engineers. Many erate a t high temperatures with fluorocarbon lubricants. of the officers and men of the district contributed greatly to Heat transfer media for high temperature operations nxiy the success of many of the projects reported here. be fluorocarbons. The unique solvent characterist>icsof tliis The field of fluorine chemistry is a t present only a small class of substances should make certain of the compounds apsegment of the chemical industry. The Freons, especially plicable for special operations in the field of solvent extracFreon 12 (CC12F2),are important in refrigeration and air coiitions. These and many other possible applications of fluoroditioning. Duiing the war the use of Freon 12 in aeiosol carbons are now feasible. bombs became important (2j. This application alone probably I n the field of organic Chemistry many times more fluorineprevented thousands of cases of malaria by exterminating containing conipounds are theoretically possible than there are mosquitoes on ships and in barracks. Theie should be many known compounds today. Because of the wide and rapidly peacetime applications of the principle of the aerosol bomb. expanding industrial and academic interest in this field, a Hydrogen fluoride is used extensively by the petroleum inhost of the theoretically possible new substances d l lie made; many are certain to find commercial applications. dustry in the synthesis of high octane gasoline by alkylation. High octane gasoline was of major importance in giving the It is significant to note that the substitution of hydrogen by Allies air supremacy. Similarly many inorganic fluorides. fluorine results in a relatively small change in boiling point compared to other halogens. For example, the substitution of notably fluorospar, boron tiifluoride, fluosilicates, cryolite, and sodium fluoride, have been commercially important for one hydrogen by fluorine in methane results in a substant'ial years. Hence, fluorine chemistry can hardly be called new. increase in boiling point, but further substitution results in a decrease in the boiling point (Table I). I n the case of the Sulfur hexafluoride has been known for some time, but because fluorine is required for its production, it has been made chloroniethanes, there is an increase in boiling point with deavailable commercially only recently. This compound is gree of substitut,ion. Another interesting example of the eifect of fluorine on boiling point is illustrated by the following: being used as an effective insulator in the high voltage electrical and x-ray fields. The fluorocarbon plastic Teflon, made Perclilorobenzene is a high melting solid. Thereas perfluoroby the polymerization of tetrafluoroethylene, is a nen- product benzene is a liquid boiling a t about the same temperature as benzene (Table I). Also, the boiling points of the perfluoroof considerable interest. This plastic is relatively stable thermally and quite inert to chemical reagents (10). The apalkanes having more than five carbon atoms are actually IoIVer than those of the hydrocarbons (Figure 1j. plication of Teflon in the generation and handling of fluorine has been especially successful. Sodium fluoroacetate is an effective rodenticide, and fluorine-containing analogs of A N D FLCORO DERIVATIVES OF R I E T H ~ S E AUD TABLEI. CHLORO D D T have been found to be useful insecticides. BESZESE The scientific and technological advancement in the generaBP, R P , Compound OC Compound ' Compound hI P , C a C tion and handling of fluorine has been so spectacular that a -161 CHI ( 6 ) -161 CeHs ( 4 ) 5.5 80 1 CH4(8) complete session of the symposium was devoted to this subCHlCl (8) -24 CeCle ( 4 ) 228 309 CHaF ( 2 1 ) - 7 8 -52 CHzClz (6) 40 C ~ F (E9 ) -13 t o -11 81-82 CHzF2 (6) ject. Before the mar fluorine a a s generated in gram quanti-82 CHCla ( 8 ) 61 CHFa (4) ties with difficulty. It could not be purchased a t any price. -128 CCla (8) T6 CFI ( 6 ) Kow fluorine can be produced a t reasonable cost on a large scale. Already it has been used in major industrial fluorinaCompounds m-ith carbon atoms to rrhich only one fluorine tions. I n 1947 fluorine will probably be offered to the indusis attached are generally unstable and, in certain instances, try by several chemical companies. Horreyer, it is predicted Ppontaneous decomposition viith the elimination of hydrogen that the largest business in this field will be in selling or licens236
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I N D U S T R I A L AND E N G I N E E R I N G CHEMISTRY
March 1947
fluoride occurs (6). On the other hand, if two or more fluorine atoms are attached to a carbon atom, the compound is generally quite stable and can be decomposed only with difficulty. For example, l,l,l-trifluoroethane can be heated at TX30" C. with fuming nitric acid without decomposition (3). Further. fluoroform and 2,2-difluoropropane are so stable t'hat they may be sulistituted for nitrogen in air, and guinea pigs can exist for several hours in such an atmosphere n-itliout a p p n r e n t harmful effects (4). This enhanced stability of CF2 and CF, groups exerts a
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WITH essentially the remarks given in this first article, E. T. McBee opened the fifty-three-paper symposium on fluorine chemistr? at the Chicago A.C.S. meeting in September 1946. The great and growing interest in fluorine chemistry stimulated by that presentation has amply justified the organizers of the symposium in their belief that here indeed is a field whose applications span virtually all branches of chemical endeavor. Only rarely does an opportunity come to present wTith such conipleteness the original scientific record of a broad field of investigation. In this instance, the importance of these new-developments in fluorine chemistry makes the disclosure-and this issue-almost historic. The present number is a monument and a tribute to the early investigators and the more recent workers whose devotion to this hazardous and difficult study has brought the subject to its present flowerThe Editors ing of utility and significance.
fungicides, germicides, fire extinguishers, solvents, fireproofing compounds, heat transfer media, and other products of benefit to society. Also, the possibilities of removing certain elements from ores or other impurities by volntilization n-ith fluorine appears t'o be an intriguing field for research. Because of the numerous and unusual possibilities in this field, the symposium attracted a great deal of interest, a n d there will undoubtedly be similar symposia in the future. This issue contains most of the papers presented before the symposiuni; several additional papers on the same suhject which have been submitted for publication since that time are also included. Khereas normally some of these papers may have appeared in the Journal of the American Chemical Society, the reviewers recommended publication of the available papers here for t'he convenience of those interested in fluorine chemistry. The contributing authors greatly appreciate the wisdom of the editors in devoting this entire issue to recent scientific and technological aclvancements in this important field of chemistry.
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5 Number Carbon A t o m s
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Figure 1. Relation between Boiling Points and Number of Carbon Atoms of Hydrocarbons and Fluorocarbons
stabilizing influence on substituents attached to adjacent carbon atoms. For example, the chlorine atom in l-chloro2,2-difluoropropane is far mole stable to heat and chemical reagents than the one in 1-chloropropane ( 7 ) . Because of these and many other interesting phenomena of fluorinecontaining organic compounds, i t is predicted that there mill continue to be an incieasing academic and industrial interest in fluorine chemistry. Peacetime products containing fluorine are eaaectetl to inelude ne,v and useful dyes, lubricant's, tanning agents, metal fluxes. fumigants, insecticides,
LITERATURE CITED
(1) Cady, G. H., and Hildebrand, J . H., J . A m . Chem. SOC., 52, 3 8 3 9 4 2 (1930). (2) Goodhue, L. D., et aZ., IXD.ENG.CHEM.,34, 1456-9 (1942); J . Econ. EntomoZ., 35,48-51 (1942); IND. EXG.CHEM.,ANAL. ED.,16,355-7 (1944) ; Soap Sanit.Chemicals, 21,No.4 , 123-7 (1945); U. S. Patent 2,321,023 (1943); Iioark, R . C . , Chem. Eng. .Vews, 22,1464-9 (1944). (3) Hass, H. B., and Best, R. D., unpublished data. (4) Henne, 8 . L., J . Am. Chem. SOC.,59, 1200-2 (1937). (5) Ibid., 59, 1400 (1937). (6) Henne, A. L., and Midgley, T., Jr., I b i d . , 58, 882 (1936). L., and Renoll, AI. W., Ibid.. 59,2434-6 (1937). (7) Henne, -1. (8) Lange, N. A . , Handbook of Chemistry, 5th rev. ed., Sandusky, Ohio, Handbook Publishers, Inc., 1944. (9) McBee, E. T., Lindgren, T. Tr., and Ligett, W ,B., ISD.ESG. CHEM.,39,378 (1947). (10) Renfrew, 11.&I.,and Lewis, E. E., Ibid., 38, 870-7 (1946). (11) Swarts, F., Bull. acad. T O Y . Belg., 1910, 113-23.
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before the S ~ m p o s i u mon Fluorine Chemistry as paper 27. Division of Industrial and Engineering Chemistry, 110th Meeting of the A ~ c , ~soCIETY. ~ ~ chicago, ~ ~ 111. ~ ~ ~ ~ ~ ~ ~ PRESENTED
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