Structure and physical properties of aluminium alkoxides. Part II: Changes in physical properties of liquid aluminium isopropoxide during storage

The density, refractive index, dielectric constant and viscosity of liquid aluminium isopropoxide have been studied. From observations for the liquid at 25°, immediately after heating at 130° and cooling rapidly, an Onsager dipole moment of 1.7‐2.5 D is calculated. During storage the physical properties change slowly. This confirms the occurrence of a molecular rearrangement reaction, which was inferred previously from molecular weight and NMR data. A further indication was obtained by the discovery of a second solid form of aluminium isopropoxide, which melts at 29.5°, whereas we have found also a form with melting point of about 137°, considerably higher than that for normal aluminium isopropoxide, 118°. The rates of changes in density and viscosity have been measured at different temperatures, from which the activation energy for the rearrangement reaction is estimated to be about 12 kcal/mole.