An unexpected product from the attempted acetal formation of 2,4,6-trihydroxybenzaldehyde

Abstract The reaction of 2,4,6-trihydroxybenzaldehyde with an alcohol in the presence of an acid catalyst resulted in the intensely colored xanthylium product instead of the intended acetal. The structure of the xanthylium species was elucidated by high-resolution mass spectrometry and NMR. Reaction monitoring by NMR revealed the presence of a dimeric non-cyclized intermediate, but not the desired acetal. A mechanism for the formation of the xanthylium species is also proposed.