Thermochemistry and Vapor Pressure of Aliphatic Fluorocarbons. A Comparison of the C–F and C–H Thermochemical Bond Energies

Abstract

The heat of formation of four organic fluorine compounds, including three completely fluorinated aliphatic compounds, was determined by a rota ting-bomb method of combustion calorimetry. An earlier technique that used sealed, fusedquartz ampoules for containing samples of volatile fluorine compounds was replaced by an improved technique that used sealed bags of a polyester film. For three of the compounds vapor pressure measurements were made by an improved method of comparative ebulliometry. The following values, in kcal. mole-1, are reported for the standard heat of formation, /fjf°298• 6, of these compounds from graphite and gaseous fluorine and hydrogen: ro-fluorobenzotrifluoride(g), -184.17; perfluoromethylcyclohexane(g), -675.3; perfluoroethylcyclohexane(g), -769.7; and perfluoro-ra-heptane(g), -789.0. These values were used with other thermochemical data to obtain a direct comparison of the C-F and C-H thermochemical bond energies in aliphatic compounds.

Orthobaric surface tension of (tetrachloromethane + tetradecafluoromethylcyclohexane) in the critical region at temperatures fromT= 303 K toT= 315 K

“…By contrast, the surface tensions of the related mixture (methylcyclohexane + tetradecafluoromethylcyclohexane) -whose surface tensions are less dissimilar than those of the present mixture -display negative aneotropy in mixtures very rich in tetradecafluoromethylcyclohexane. Figure 5 shows the vapour pressures p* c of pure tetrachloromethane, according to Hildebrand and McDonald (34) and Boublik, (35) and p* t of pure tetradecafluoromethylcyclohexane, according to Good et al (36) Unusually, the vapor pressures of the components in the present mixture are almost equal -as figure 5 illustrates -and the mixture is thus very close to Bancroft-point behaviour at all temperatures and not only within the range considered here. Although there appear to have been no measurements of the vapour pressures of the mixture, it is obvious .…”

The standard enthalpies of formation of 2-methylbiphenyl and diphenylmethane,

“…(15)(16)(17) A rotating-bomb calorimeter (laboratory designation BMR II) (18) and two platinum-lined bombs (laboratory designation Pt-3b and Pt-5b) (19) with internal volumes of 0.393 4 dm 3 and 0.395 4 dm 3 , respectively, were used without rotation. For each experiment, a volume 1.0·10 −3 dm 3 of water was added to the bomb, and the bomb was flushed and charged to the pressure 3.04 MPa with pure oxygen.…”

The thermodynamic properties of 9-methylcarbazole and of 1,2,3,4-tetrahydro-9-methylcarbazole

“…Parity plot comparing sublimation pressures measured by Jim6nez et al (49) with values calculated using equation (19 inclined-piston gauge; water or decane refers to which material was used as the standard in the reference ebulllometer; T is the temperature of the experimental Inclined-piston pressure gauge measurements or, for ebulliometrlc measurements, of the condensation temperature of the sample; the pressure p for ebullion'letrlc measurements was calculated from the condensation temperature of the reference substance; Ap iS the difference of the calculated value of pressure from the observed value of pressure; _1is the propagated error calculated from equations (1)and (2) TABLE15.…”