Base-strength distribution studies of solid-base surfaces

A method has been developed for the determination of the base-strength distribution of solid surfaces. The present method consists of the titration of solids suspended in cyclohexane with benzoic acid, using a series of H− indicators. The base-strength distribution of solid surfaces has been measured by this method for alkaline-earth oxides and some other solid bases. Alkaline-earth oxides increased remarkably in base strength upon heat treatment in vacuum. The base strength of these oxides proved to decrease in the order SrO(H− ⩾ 26.5) ≈ CaO(H− ⩾ 26.5) > MgO(H− = 18.4 to 26.5), in accordance with the observation by Krylov et al. and also with the order expected from the partial negative charge of combined oxygen anions in these oxide surfaces. A distinct distribution of base strength was observed on these oxide surfaces. No basic sites having an H− equal to or higher than 12.2 were observed on the surfaces of ZnO, ZrO2, ThO2, or Na2CO3. The catalytic activity and selectivity of alkaline-earth oxides in the elimination of hydrogen chloride from 1,1,2-trichloroethane were quantitatively interpreted from the observed base-strength distribution.