Abstract:

An efficient onepot synthesis of amidoalkyl naphthols is described. This involves the three-component Ritter-type reaction of β-naphthol, aromatic aldehyde and amide or urea catalyzed by sulfonic ionic liquid, 1-methyl-3-propanesulfonic acid immidazolium hydrogen sulfate [MIMPS][HSO₄]. The results show that under solventfree condition at 125 ℃ and n(β-naphthol)∶n(aromatic aldehyde)∶n(amide or urea)∶n([MIMPS][HSO₄])=1∶1∶1.3∶0.1 for 5～40 min, the yield of amidoalkyl naphthols was 85%～97%. The product could be separated simply by filtration after the reaction. The ionic liquid was recycled four times without apparent decrease in catalytic activity. The factors which influenced the multi-component reaction were discussed including the structure of aromatic aldehyde and amide or urea. A possible mechanism was postulated as well.

Key words: acidic functionalized ionic liquid, Ritter-analog reaction, aromatic aldehydes, amide, amidoalkyl naphthols