A novel process for the preparation of high-purity zirconium, hafnium, tantalum and niobium alkoxides (alcoholates), novel tantalum and niobium compounds and a process for their preparation are provided. The process comprises the steps of mixing crude metal alkoxides M(OR).sub.x having a halogen impurity of at least 0.05 wt. %, with an alcohol ROH, in which R is a C.sub.1-C.sub.12-alkyl radical, and subsequently or simultaneously metering in an excess of ammonia, based on the amount of mononuclear or polynuclear halogen-containing metal alkoxides.