NOTES
Jan., 1961 reduced this solid formation to a negligible amount, presumably due to the more rapid transfer of heat from the reaction zone. Materials.-BzF4 was prepared by the method of Finch and Schlesinger in a vacuum line equipped with mercury float valves. The uamples, ranging from 1.2 to 1.5mmoles, were measured in a volume of 270 ml. and condensed in glass ampoules of about 7 ml. Chlorine was purified by fractional bulb-to-bulb distillation. Experimental Procedure .-The reaction vessel, calorimeter and erformarice of the runs were as previously dea run, the gas in the reaction vessel scribed. was sealed in a tube with mercury, shaken overnight to remove chlorine, and measured in the same calibrated bulb used for the sample measurement.
%'allowing,
Results.-Results in Table I. HEATOF 5 5 25 25 25
2 3 4 5
0 10 10 8 10
BCh, -97.1', AH? (B2F4)is calculated to be -342.0 kcal. mole-'. Using $18.3 for AHfo(F,g)*and +135.2 f 4 for AHrO (B, g)6the thermochemical B-F bond energy in BF, is 153.3; assuming this to be unchanged in B2F4, E(B-B) is 72.4. This is to be compared with a value of 79.0 derived for E(B-B) in B2C14 by the same method. This calculation is probably less valid for B2F4 than for B2C14; in B2C14 the B-CI distance is nearly the same as in BC13 whereas the B-F distance in B2F4is roughly 0.03 A. longer than in Also the B-B distance in B2F4 is roughly 0.08 A. shorter in B2F4than in BzC14. (7) W. H. Johnson, R. G. Miller and E. J. Prosen, J . Research N B S .
(1959).
62, 213 (8) F. D. Rossini, et al., Circular of the National Bureau of Standarde 500, 1952, (9) L. Trefonas and W. N. Lipscomb, J. Chena. Phys., 28, 54
TABLE I REACTION OF BtF4 WITH Clz
Temp., Helium, Run "C. cm.
1
of the measurements are given
179
Mol. wt.
98.1
< 99.0
