Friedel - Crafts-type reaction of benzaldehyde with benzene. Diprotonated benzaldehyde as the reactive intermediate

Article abstract of DOI:10.1021/ja00150a007

Benzaldehyde (1) reacted with benzene in the presence of trifluoromethanesulfonic acid (TFSA) or a mixture of TFSA-trifluoroacetic acid (TFA) to give triphenylmethane (2), diphenylmethane (3), and triphenylmethanol (4). The initial formation of the intermediate 2 was followed by the formation of 3 and 4 as the final products. The total yield of the products 2-4 became higher in the presence of stronger acids, which indicated that the further activation of monoprotonated 1 was required in this reaction. O,O-Diprotonated benzaldehyde was proposed as the reactive intermediate, on the basis of the relationship between yield and acidity and the result of the NMR investigation.