AbstractThe thermal stabilities of Zr(OEt)4, Zr(OPrf)4, Zr(OBut)4 and Zr(OC5H11‐tert.)4 have been studied in an all‐glass apparatus under constant pressure at various temperatures and pressures. Most work was carried out on the tertiary alkoxides and these exhibited an induction period which was very sensitive to traces of oxygen or the products of decomposition. The latter were always a mixture of olefin and tert.‐alcohol and a solid of composition in the range Zr2O3(OR)2,‐ZrO2. It is concluded that under appropriate conditions the tert.‐butoxide or tert.‐pentyl oxide are stable enough to be fractionally distilled at 250°c under 760 mm. or 175 mm, pressure, respectively.