The normal alkoxides, Ti(OC,H,,+,), where n = 2, 3, 4, 5, 6, 7, and 8, and Zr(OC,H,,+,), where n = 2, 3, 4, 5, 6, and 8, have been prepared and their molecular weights and boiling points measured. Molecular complexity is practically independent of chain length while boiling points increase linearly with molecular weight. Structures for the complex alkoxides are discussed. Vapour pressures and vapour densities were measured for zirconium tetraethoxide and tetraisopropoxide and it is suggested that the vaporisation process is [Zr(OR)J, (liquid) + nZr(OR), (vapour), and that the energy of intermolecular attraction is ca. 18 kcals./mole. Entropies of vaporisation for the n-alkoxides of silicon and titanium increase with chain length, and this behaviour is discussed in terms of molecular " entanglement " in the liquid state.

Vapour-pressure measurements in the range 0.05-50 mm. have been made on titanium tetra-tert.-butoxide and -amyloxide, by a static method, in an all-glass apparatus incorporating a novel type of spoon-gauge. The apparatus and technique were developed for compounds which are sensitive to hydrolysis and to thermal decomposition. The computed results conformed to equations of the type, log P = C -xlTy log T for certain ranges, but it is believed that their extrapolation is valid.RECENT work in these laboratories on the preparation of volatile metal alkoxides suggested the possibility of separating and purifying metals by fractional distillation of the alkoxides. It was necessary therefore to determine vapour pressures accurately over a wide range of pressures. In addition these data were required for calculations of thermodynamic properties and thermochemical data. Preliminary measurements of the boiling points of monomeric alkoxides of titanium,l zirconium,l and hafnium 2 at various pressures had revealed that their volatilities were in the unexpected order, Hf(OR), > Zr(OR), > Ti(OR),, whose theoretical implications provided yet another need for vapour-pressure measurements of the highest possible accuracy. Considerable difficulties were experienced in attempting these accurate measurements and the present communication is mainly devoted to describing the experimental method. The titanium alkoxides were studied first because experience has shown that they are less difficult to deal with than the zirconium and the hafnium compounds. The results obtained were of sufficient accuracy to require a " three-constant " vapour-pressure equation.

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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 densities and surface tensions of several alkoxides of titanium, zirconium, tin, cerium, and thorium have been measured over the temperature range 25-40' and the parachors have been calculated. Analysis of the parachors by the method used for alkyl orthogermanates revealed some characteristic structural features. Parachor " contractions " in titanium n-alkoxides are consistent with the polymeric nature of these compounds and, in the monomeric tertiary alkoxides of titanium, zirconium, tin, cerium or thorium, suggest the presence of considerable intramolecular congestion accentuated by metal-oxygen bond contraction.