Volatile Methoxides of Aluminium and Zirconium

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.