Journal of Molecular Catalysis A-Chemical, Vol.169, No.1-2, 185-191, 2001
Regioselectivity in the preparation of 2-hydroxy-4-methoxy benzaldehyde from resorcinol
Three reactions, namely, Reimer-Tiemann reaction of resorcinol, one pot Reimer-Tiemann reaction of resorcinol and its methylation and finally Reimer-Tiemann reaction of resorcinol monomethyl ether were studied. Better selectivities were observed in the first two reactions when beta -cyclodextrin (beta -CD) and its derivatives were employed. The formation of 2,4-dihydroxybenzaldehyde and 2-hydroxy-4-methoxybenzaldehyde from the first two reactions showed better conversion than the control reaction. In the process, 70.0% 2,4-dihydroxybenzaldehyde was detected in the presence of 1 equivalent of beta -CD and 48.2% 2-hydroxy-4-methoxybenzaldehyde was detected in the presence of 0.2 equivalent of HP beta -CD. However, Reimer-Tiemann reaction of resorcinol monomethyl ether resulted in only a marginal increase (43.9%) of 2-hydroxy-4-methoxybenzaldehyde (I) in the presence of 0.2 equivalent of P-CD as compared to the control (35.2%). The observed results were explained in terms of specific orientation of resorcinol inside the P-CD cavity which facilitates the attack of dichlorocbenzene from the narrower end on the electron rich ortho position to the -OH of resorcinol leading to the formation of 2,4-dihydroxybenzaldehyde or 2-hydroxy-4-methoxybenzaldehyde(I).