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 in 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.

Direct Phenolysis Reactions of Unactivated Amides into Phenolic Esters Promoted by a Heterogeneous CeO2 Catalyst

“…This catalytic system not only offers a facile means to cleave the amide C−N bond, but also significantly promotes the use of amides and phenols as important building blocks for the synthesis of valuable esters. Moreover, the obtained results provide a better understanding of the catalytic behavior of CeO 2 , which has been of significant interest recently …”

Application of Infrared Spectroscopy in Catalysis: Impacts on Catalysts’ Selectivity

“…Therefore, a lot of attention is paid in developing alternative heterogeneous catalysts. Among the different heterogeneous catalysts reported in the literature [42,43], nanocrystalline ceria (nCeO 2 ) stands as a very promising catalyst in the dehydration of a variety of aldoximes (including alkyl and cycloalkyl aldoximes) to the corresponding nitriles at moderate temperature (149°C) with yields around 80-97% [44]. The catalyst shows good stability and recyclability after several uses.…”

Simultaneous quantitative structure‐activity relationship analysis of catalyst activity and selectivity in the direct oxidation of C―H bonds

“…Catalysts, which are amazing compounds that are not consumed in a reaction, make it possible for chemists to either break or make chemical bonds within and/or between various compounds efficiently and selectively. Catalysts allow sparsely functionalized compounds to be converted into more useful ones . Not surprisingly, these value‐added compounds occupy a key role in many industries ranging from fuels and plastics to drugs and fertilizers.…”