Karr, " Physical Properties of Low-Boiling Phenols. the Interior, 1957, Information Circular 7802. F. p. 99.929 & 0.006 0.848" f 0.004" 40.84" f 0.01" F. p. 99.963 f 0.002 0-596 f 0.009 30.97 f 0.01 M. p. 99.917 & 0.020 0.749 f 0-040 12-16 f 0.01 F. p-99.963 f 0.021 0.915 f 0.051 34-65 f 0.01 M. p. 99.928 f 0.005 0.502 f 0.019 72-53 f 0.01 M. p. 99.972 f 0.002 0.576 f 0.030 24.52 f 0.01 M. p. 99.896 f 0.020 0.727 f 0.008 74.77 f 0.01 F. p. 99.886 f 0.008 0-558 f 0-016 45.56 f 0.01 M. p. 99.971 & 0.005 0.727 f 0.020 65-09 f 0.01 M. p. 99.960 f 0.004 0.520 f 0.059 63.24 f 0.01 I;. p. €or 100% purity 40.90" f 0.01" 30.99 & 0.01 34.69 -J= 0.02 72.57 f 0.02 24.54 & 0.01 74.85 f 0-02 45-62 & 0.01 65.11 f 0-01 63.27 f 0.02 (tf, 0 ) f 0-02Vapour pressure-temperature relationships, normal boiling points, values of (dtldp) 760 mm., and latent heats of vaporization. The vapour pressures of the liquid and solid xylenols were measured by ebulliometric and gas-saturation procedures previously described.4~ 1 3 ~~4 Detailed results for the six xylenols are given in Table 2.Antoine equations [i.e., equations of the form log,, P = A -B/(t + C)] were fitted to the data for higher temperatures, and the two-constant equation log,, P = A -B/(t + 273) was used for the lower temperature range. Table 3 gives the constants of these equations and Table 4 shows the normal b. p.s; values of (dt/dP),so-.

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The vapour pressures of phenol, o-, m-and p-cresol have been measured over the temperature ranges 0-40°C and 110-200°C. The results have been fitted to two-constant equations, loglo P = A -B/(t + 273) for the lower temperature range and to Antoine equations, loglo P = A -B/(t + C) for the higher range. Values for the normal boiling points, for df/dP, and for heats of vaporization are given.The industrially important phenolic compounds (phenol, cresols and xylenols) have been prepared at this laboratory in a high state of purity for measurement of their physical and thermodynamic properties and for issue as standard samples.1 The measurements of vapour pressures of phenol, o-, m-and p-cresol are reported here.Accurate data on the vapour pressures of these compounds have several uses, e.g., in connection with fractional distillation and for calculation of activity coefficients and heats of vaporization. The heat of formation of a compound at 25°C in the ideal gas state can be calculated from the heat of combustion if the heat of vaporization of the compound at 25°C is known. An estimate of this quantity for those substances which are liquid at 25°C can be obtained by extrapolation of vapour pressure-temperature equations for data at higher temperatures but the errors involved are likely to be large compared with the errors in the heat of combustion measurements. We have therefore measured the vapour pressures of liquid m-cresol and solid phenol, o-and p-cresol in the temperature range Most of the published data 2-9 on the vapour pressures of phenol and its homologues were obtained before the development of reliable methods of determining purity. References to earlier work have been given by Stull.2 The most recently published measurements on phenol and phenol derivatives are those of Terres et aZ.,9 who measured pressure to the nearest millimetre and temperature to 0.1"C or, in some cases, to 1°C. Data of similar accuracy have been reported by Goldblum et aZ.4 Dreisbach and Schrader 7 have used materials of high purity (> 99.9 moles %) and refined techniques of measurement to determine the vapour pressure against temperature relationships for phenol, o-cresol, and p-cresol at six pressures in the range 50-76Omm Hg. The only low-temperature vapourpressure measurements reported for phenols are the accurate measurements by Balson 5 for phenol itself.The apparatus and techniques used for the present measurements in the range above 100 mm Hg have been described previously.10 Several methods of measurement of low vapour pressures have been developed,lls12 three of which were considered for the phenols. They were the Knudsen effusion technique, the gas saturation or transpiration method, and a direct method using a diaphragm manometer. The vapour pressures of some organic compounds have been determined by the Knudsen effusion method 1~1 4 but this technique does not appear to be suitable for making measurements on phenol or the cresols in the range 0-40°C because theory requires that an impractically small effusion hole ...

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