Kinetic Analysis of Consecutive/Parallel Transformation of Furfural to Biomass-Based Primary Amide by Using a “Concentration–Time” Integral

A fundamental understanding of biomass-based transformation of furfural (1a) to 2-furamide (4a) is highly desirable for the extension of amide chemistry. In this research, direct amidation of 1a with hydroxylamine to 4a was investigated by using a Cu-doped Co3O4 (Cu/Co3O4) catalyst with 2-furancarboxaldehyde oxime (2a) and 2-furonitrile (3a) as detectable intermediates. Mechanism research has demonstrated the presence of two competitive, independent, and parallel reaction pathways: (i) direct 2a-to-4a rearrangement (the Williams mechanism), and (ii) 2a-to-3a dehydration followed by 3a-to-4a rehydration (the classic mechanism) with the rehydration as the rate-determining step. Subsequent kinetic analysis by "concentration–time" integrals revealed that the Williams mechanism was always the predominant reaction pathway, with the reaction rate constant being almost 22 times greater than that of the classic mechanism. The catalytic performance of Cu/Co3O4 was correlated to its surface concentration of oxygen vacancy and surface acidity. The insights thus highlight a kinetic understanding of a complex consecutive/parallel transformation of biomass-based aldehyde for amide product.