A QUANTUM-MECHANICAL STUDY ON THE REACTIVITY AND ACIDITY OF THE LIALO2-BENZOIC ACID SOFT CHEMICAL-REACTION

Solid alpha-LiAlO2 exchanges Li+ for H+ when in contact with molten be nzoic acid yet gamma-LiAlO2 does not. Electronic structure calculation s on both solid phases show that the reason for Li being substitutable solely in alpha-LiAlO2 arises mostly from the difference in Li electr ophilicities. Thus, the less acidic Li atom in the alpha-phase is exch anged against a proton whereas the Li atom in gamma-LiAlO2 is too stro ng a Lewis acid for the proton to ''drive out''. Furthermore, while Li atoms are more weakly bonded within the structural matrix than Al ato ms, there is a significantly smaller Li-O binding energy in the alpha- compared to the gamma-phase and the less acidic Li atom (alpha) is th ermodynamically more labile. Finally, one finds a large difference in the energetic behavior upon dislocation of a Li atom from its equilibr ium position in the alpha- and gamma-phases. Despite having a high act ivation barrier, there is a finite kinetic chance for a Li atom to esc ape from its equilibrium position only in alpha-LiAlO2.