Reaction of piperidine with formaldehyde over alumina and spinel aluminates

The reaction of piperidine with formaldehyde over γ-alumina, Na+-γ-alumina, NiAl2O4 and CuAl2O4 was studied as a model system in order to understand the mechanism and selectivity of alkylpyridine formation from piperidine and carbonyl compounds. Along with the expected 3-picoline, 2-picoline and other products were also formed. The selectivity for 3-picoline was high on γ-alumina whereas on NiAl2O4, 2-picoline was selectively formed. The formation of the different products has been rationalized and a probable mechanism for the formation of 2-picoline has been presented.