Strong bases from alkaline and alkaline-earth metal carbonates were generated in situ by adding a small amount of acetic acid at reflux in toluene under water-free conditions. Their basic strength reached superbasicity thus changing the color of 4-chloroaniline (H- = 26.5). The high conversion of ethyl acetate in its self-condensation over decomposed carbonates, which require strong basicity to abstract protons from ethyl acetate (pK(a) = 25), also confirmed the formation of strong bases. Adding acetic acid during the reaction indicated that metal oxides-decomposed materials from carbonates-were responsible for their high catalytic activity. The lack of sufficient coordination of in situ generated metal oxides was considered to be a plausible cause for their strong basicity.