NOTES
Oct., 1961 shown curves illustrating the selective adsorption of SF6 from a 50% air and 50% SFa misture. The SFs adsorption characteristics of the sieve are found to be independent of the air concentration. The SFa commerlcially available contains impurities Nz, A. and H20. With the exception of of CF,, 02, water, and slight amounts of nitrogen, the other impurities are not adsorbed by the sieve and thus this provides a means for purifying SFs. Mild heating removes the S S and not the water. The SF6 interacts through an induced dipole whereas water adsorbs by dipolar interaction.
1913
for the C-F system, AHa(CF2) = 243 kcal./mole and AHr0(CF2)= -36 kcal./mole. Thus, it appears that the heat of formation of CF2(g) is considerably more negative than previously thought with the correct value in the range -35 f 10 kcal./mole. REACTION OF ATOhlIC HYDROGEN WITH SOLIDS AT - 10501 BY VINCEXTJ. DECARLO A N D F. 0. RICE Deparfment of Chemistry. Georgetown Unzteraly. Waahington 7 D . C . Received May 1 , 1961
T H E HEAT O F FORMATION OF CF2
This work was started with the idea of synthesizing LiH3. The fundamental notion is that BYLEOBREWER, JXTN L. MARGRAVE,' RICHARD F. PORTER negative ions tend to grow in order to give more AND KARLwIEL.4ND room for the electronic cloud and consequently one Department o/ Chemastvy, Univerrity of Cdifornra, Berkeley. Cdafornia might expect, given proper conditions, that the Received Aprrl 67, 1961 proton in lithium hydride could incorporate two Available data for the heat of formation of CFs hydrogen atoms to form the ion H3-. The method are based on the general analogy of the C-F system used was that developed by Klein and Scheer2 with the C-H system? or on rates of reaction of in which hydrogen atoms react with various sub9 a with fluorinated metharies,3 and suggest AHtO stances frozen on a liquid nitrogen-cooled surface. -18 kcal./mole. N o lower limit on the heat has Our results (largely negative) are shown in Table I. been suggested. Margrave4has concluded recently TABLE I from a mass spectrometric study of C2F4 and the .4CTION O F ATOMIC HYDROGEN ON VARIOUS SUBSTANCES appearance potential of CF2+that LHfo = -30 2 UNDER VARIOUS TEMPERATURES 10 kcal./mole. Substance Temp., 'C. Resiilts Further evidence regarding CF2 has been de- 195 KO reaction duced by deterrnining the lowest temperature at I,i 100 Fast reaction which CF2 bands may be detected in absorption in 1,1 the system C F ~ g r a p h i t e . ~The fir$ faint, but Ka, Hg, Cd, M g Zn, Bi, G e , G a - 195 No reaction clearly visible bands (2487 and 2457 A.) appear a t - 195 Very slow reaction !830°K. from th? reaction CF4(g) C(s) = 2CF,- CZl -195 H atoms go t o H2 nhirh i q (8) with PCF,= 0.18 atin. From the very diffuse B3 100 absorbed. Yo further renature of the bands, it is likely that a minimum of actions 0.0015 mm. of C:FZ a t 1800°K. is required for de- 105 Apparently an unstable tection, while the maximum amount is probably CIl hydride firht forms and 0.015 mm. a t 1800°K.. depending on the transition then decomposes as probability. These pressures, along with the coiicn increa~es known heat of formation of CF4(g),6 and other - 195 V e r y slow reartion standard thermodynamic functions, lead one to HN, - 150 Very slow rraction calculate AHrOtCF,) i -30 kcal./mole a t 298OK. - 195 Very slow reaction X comparison also can be made with the Si-C1 COS - 195 N o reaction system for which Schafer and Nickl' have reported Acetic anhydride the heat of formation of the analogous molecule n-Butylamine - 195 N o reaction - 195 No reaction Sic12 as -30 kcal./mole. One can compare the Isobutylamine - 105 X o reaction heat of atomization of SiCI, (192 kcal./mole) with Ethyl alcohol the heat of atomization of Sic14 (365 kcal./mole) Amyl alcohol - 195 No reaction and establish the ratio Acetone - 195 Very slow reaction
+
A similar value For this ratio appears t,o hold for the Si-F system8 If exactly the same ratio holds (1) University of Wisconsin, Madison, Wisconsin. (2) R. Potocki and D. Mann. Natl. Bur. Standards Report 1439, February 15. 1952. (3) J. Reed and 1%. liabinovitch, J. Phys. Chem., 61, 598 (1957). (4) J. L. Margrave, J. Chem. Phys., 31, 1432 (1959). (5) J. L. Margrave a n d K. Wieland, J. Chem. Phys.. 21, 1552 (1953); X.F. Porter a n d K. Wieland, unpublished work, 1953. ( 6 ) c. A. Neugebeuer and J. L. Margrave, J. Phys. Chem., 60, 1318 (1956). (7) H. Schafer a n d 1. Nickl, %. anorg. u. allgem. Chon., 274, 250 (1953). ( 8 ) A. Kanaan a n d J L. Margrave, unpublished work, University of Wiscousin :961.
n-Propyl alcohol Carbon tetrachloride Isobutyl alcohol sec-Butyl alcohol &Butyl alcohol n-Butyl alcohol
- 195 - 195 - 195 - 195 - 195 -195
Ethyl iodide
- 195
Very slow reaction Very slow reaction Slow reaction slow reaction Slow reaction Slow reaction (faster thxn the three previous) Fast reaction
To our very great surprise, ethyl iodide reacts readily with hydrogen atoms at - 195' ; the white solid turns orange and gives a positive test for free iodine using starch indicator. We positively (1) Presented at the Fifth International Svmpotuum 011 Free Radicals. Uppsala. Sweden, July, 1961. (2) R. Klein a n d M. D. Scheer, J. Pbya. Chem., 62, 1011 (1958).
