Nanocrystalline CeO2 As A Highly Active And Selective Catalyst For The Dehydration Of Aldoximes To Nitriles And One-Pot Synthesis Of Amides And Esters

Abstract

The dehydration of aldoximes into nitriles has been performed in the presence of various metal oxides with different acid-base properties (Al2O3, TiO2, CeO2, MgO). The results showed that a nanocrystalline CeO2 was the most active catalyst. An in situ IR spectroscopy study supports a polar elimination mechanism in the dehydration of aldoxime on metal oxide catalysts, in which Lewis acid sites and basic sites are involved. The Lewis acid sites intervene in the adsorption of the oxime on the catalyst surface while surface base sites are responsible for the C1-H bond cleavage. Thus, the acid-base properties of nanocrystalline CeO2 are responsible for the high catalytic activity and selectivity. A variety of aldoximes including alkyl and cycloalkyl aldoximes have been dehydrated into the corresponding nitriles in good yields (80-97%) using nanosized ceria which moreover resulted a stable and reusable catalyst. Additionally, it has been showed that a variety of pharmacologically important products such as picolinamide and picolinic acid alkyl ester derivatives can be obtained in good yields from 2-pyridinaldoxime in a one pot process using the nanoceria as catalyst. Keywords: nanocrystalline CeO2, acid-base catalyst, aldoxime dehydration, nitriles, one-pot synthesis, amides, esters.