Volatile Methoxides of Aluminium and Zirconium

Abstract

THE methoxides of the alkali metals, magnesium, aluminium and zirconium were considered to be non-volatile due to their being either ionic or highly polymeric covalent in nature. Thus by contrast the penta-methoxides of quinquevalent niobium¹ (dimer), tantalum² (dimer) or uranium³ (trimer) may be distilled under a pressure of 0.1 mm. mercury. According to our structural theory for metal alkoxides⁴ it seemed possible that the degree of polymerization of aluminium trimethoxide or zirconium tetramethoxide could be as low as 8-fold and approximate calculations suggested that such compounds might be volatile at temperatures greater than 200° C. Moreover, recent studies on the thermal stability of metal alkoxides⁵ suggested that the methoxides would remain stable up to about 400° C. Accordingly we have attempted to sublime some of the ‘non-volatile’ methoxides in an all-glass molecular still at very low pressure.