Superacid-Catalyzed Condensation of Benzaldehyde with Benzene: Study of Protonated Benzaldehydes and the Role of Superelectrophilic Activation

Under superacid conditions benzaldehyde reacts readily with benzene to give triphenylmethane in high yield. Experimental evidence supports the involvement of diprotonated benzaldehyde in the reaction. Ab initio calculations at the correlated MP2/6-31G* level on the structures and energetics of the possible dicationic intermediates indicate that the reactive intermediate involved is preferably the O,C(aromatic)-diprotonated dication and not the O,O-diprotonated system. IGLO-calculated ¹³C NMR chemical shifts of protonated benzaldehyde were compared with the experimentally observed data.