762. Vapour pressures of metal alkoxides. Part III. Hafnium tetra-t-butoxide and -t-pentyloxide

Abstract

By D. C . BRADLEY and J. D. SWANWICK.The vapour pressures of hafnium tetra-t-butoxide and -t-pentyloxide have been measured over the range 0.05-50 mm. Hg by the static method. These results were confirmed by hypsometric measurements a t pressures > 8.0 mm. It is shown that for t-butoxides and t-pentyloxides the order of volatilities is Hf > Zr > Ti over the pressure range studied. From the vapour-pressure equations it is deduced that the molar heats of vaporisation are markedly temperature-dependent.IN previous papers we reported vapour-pressure measurements on the t-butoxides and t-pentyloxides of titanium and zirconium,l in which we used an elaborate technique for studying compounds which are extremely readily hydrolysed and susceptible to thermal decomposition. These results proved that the zirconium compound was more volatile than its titanium analogue over a wide range of pressures. In view of the possibility of separating hafnium and zirconium by distillation of their alkoxides, it was necessary to obtain accurate data on the hafnium compounds. In addition, these results should be of special interest from the theoretical viewpoint in connexion with the relation between volatility and molecular eight.^ We now present results for hafnium tetra-t-butoxide and -t-pentyloxide obtained by the same method as for titanium and zirconium derivatives.The significance of these results is discussed. EXPERIMENTALHafnium A Zkoxides.-These were prepared by essentially the methods reported previously.4 Hafnium contents were determined by precipitation of hafnium hydroxide (cf. zirconium) followed by ignition to HfO,. Careful analyses of (i) dipyridinium hafnium hexachloride (C,H6N),HfC1,, (ii) hafnium isopropoxide solvate Hf (OPr') ,,PriOH, (iii) hafnium tetra-tbutoxide, and (iv) hafnium tetra-t-pentyloxide established that the zirconium content of the hafnium was ( 0 . 5 % . In view of the similar volatilities of the hafnium and the zirconium compounds and the accuracy of the measurements, it was considered unnecessary to correct the results for this small zirconium impurity.Vapour-pressure Measurements.-The static and the hypsometric method were applied as previously described.Results.-Hafnium tetra-t-butoxide. The results are presented in Table 1. The vapour pressures in italics or in parentheses were not used in computing the vapour-pressure equation (1).The plot of log P versus Results in italics were obtained by the hypsometric method.

The Rankine–Kirchhoff approximations for moist thermodynamics

“…The fact that these works were published in different languages and different countries likely also explains why the equation has been referred to by a bewildering array of names: Rankine–Kirchhoff (Cornelissen and Waterman, 1956; Biddiscombe and Martin, 1958; Waldenstrøm and Stølevik, 1980; Mishra and Yalkowsky, 1991; Yalkowsky and Mishra, 1991; Griesser et al ., 1999; Lobo and Ferreira, 2001; Wisniak, 2001; Smith, 2002; Tetko, 2007), Kirchhoff–Rankine (Laby, 1908b; Bradley and Swanwick, 1958; 1959; Davies and Taylor, 1964; Miller, 1964; 1966; Mazdiyasni et al ., 1967; Roder, 1977), Kirchhoff–Rankine–Dupré (Laby, 1908a; Smith and Menzies, 1910; Menzies, 1919; Kaye and Laby, 1921; Hine, 1924; Emmet, 1925; Holm, 1933; Gottschal and Korvezee, 1953; Jobson, 1973; Novikov, 1976; Wilcox and Bauer, 1991; Bogillo and Staszczuk, 1999; Mianowski and Urbańczyk, 2017), Rankine–Dupré (Cragoe et al ., 1920; Peirce, 1929), Dupré–Rankine (Juliusburger, 1900; Bittrich et al ., 1962; Siedler et al ., 1969; Schmeling and Strey, 1983), and Kirchhoff–Dupré–Rankine (Le Fèvre and Tideman, 1931). …”