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The new alkoxides Nb(OR),, where R = Me, Et, Prn, Bun, or n-pentyl, have been prepared by reactions involving niobium pentachloride, the alcohol, and ammonia, or by alcohol-interchange involving niobium pentaethoxide. Boiling points under reduced pressure and ebullioscopic molecular weights in benzene, in toluene, and in the parent alcohols were determined. The niobium n-alkoxides are less stable than the corresponding tantalum compounds. The volatilities and molecular complexities of the niobium and tantalum n-alkoxides are discussed from the theoretical viewpoint.THE preparation and properties of some tantalum penta-n-alkoxides have recently been described.l In view of the chemical similarity between niobium and tantalum it seemed worthwhile to investigate the alkoxides of niobium. Additional interest was centred on the relative volatilities of corresponding niobium and tantalum alkoxides because of the possibility that the effect of molecular weight on volatility might be apparent. This communication deals with the rt-alkoxides Nb(OR),, where R = Me, Et, Prn, Bun, and ut-pentyl.These compounds may be prepared by either of the methods :Niobium pentamethoxide is a white crystalline solid, m. p. 60" [cf. Ta(OMe),, m. p. 50"], but the other rt-alkoxides are pale yellow liquids. The ease of hydrolysis in water appears to parallel the water-miscibility of the parent alcohols. A notable feature of the niobium rt-alkoxides is the decrease in thermal stability with increase in length of the alkyl chain in contrast to the behaviour of the corresponding n-alkoxides of tantalum. Thus distillation of niobium ut-pentyloxide causes decomposition even at 0.1 mm. whereas tantalum rt-pentyloxide boils unchanged at a higher temperature. The boiling points of niobium and tantalum rt-alkoxides under reduced pressure are presented in the Table : their main

described. These compounds distilled under reduced pressure without change in composition and the possibility that titanium exhibits here a covalency of 5 is considered. The new alkoxides TiCl,*OR where R = Me, Et, Pri, and Bun were readily obtained from the rapid radical-interchange reaction between the tetrachloride and the appropriate tetra-alkoxide. Certain of the titanium chloride alkoxides disproportionate when heated under reduced pressure.TITANIUM CHLORIDE ETHOXIDES have been known since 1875 when DemarCay (Compt. rend., 1875, 80, 51) reported that the reaction between titanium tetrachloride and ethanol led to the formation of a crystalline solid to which he assigned the formula TiCl(OEt),,HCl. Sixty years elapsed before the error in this formulation was pointed out and the correct fonnula TiCl,(OEt),,EtOH deduced by Jennings, Wardlaw, and Way (J., 1936, 637). In addition these authors demonstrated that in general the reaction between titanium tetrachloride and an alcohol took the course : TiC1, + 3ROH + TiCl,(OR),,ROH + 2HC1 Further it was shown that titanium monochloride triethoxide could be prepared from titanium tetraethoxide and acetyl chloride :

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.