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

Abstract

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 Co 3 O 4 (Cu/Co 3 O 4 ) catalyst with 2-furancarboxaldehyde oxime (2a) and 2furonitrile (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 ratedetermining 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/Co 3 O 4 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.

Selective Construction of a Biomass-Based Secondary Amine by Hydrogenative Homocoupling of Nitrile Using an Iridium Complex in a Metal–Organic Framework

“…–1 ) over the catalyst surface is much stronger than in the case of 1b (1.33 × 10 –4 mmol 1b g Catal. –1 ), which is presumably attributed to a two-point interaction of 1a on the catalyst surface by yielding O furan –M and N nitrile –M bonds (Scheme d) …”

“…The kinetic analysis of the hydrogenative homocoupling was then performed. The plot of 1a reaction rate (denoted as r 1a ) against reaction time ( t ) for 1a -to- 6a transformation was then calculated by differentiating the corresponding curve of 1a concentration ([ 1a ]) against reaction time (Figure S3, Supporting Information) Figure a thus shows the resulting r 1 a – t curves by using the 1.0%-Ir-bpy/UiO-67 catalyst at various reaction temperatures.…”

“…Figure e thus supports the linear relationship between ln­( A 0, 18a / A t , 18a ) and t , accordingly yielding the corresponding k obs and k 2 according to eq (Table ). , …”

“…Figure 8e thus supports the linear relationship between ln(A 0, 18a /A t, 18a ) and t, accordingly yielding the corresponding k obs and k 2 according to eq 4 (Table 2). 63,66 Similarly, the kinetics of 5a (C�N bond) insertion into 18a to give 20a was further investigated (Figure 8a). The resulting kinetic UV−vis spectroscopy shows a red-shift of maximum absorption from 420 to 459 nm after the insertion reaction (Figure 8c).…”

“…This observation is presumably attributed to the formation of relatively stable intermediate E (Scheme 2a) with a five-membered transition state of Ir-mediated metallacyclic structure. 63,67,68 Enonitriles (1f and 1r) also exhibit higher TOF values due to the quick saturation of their C�C double bonds at the initial stage. In contrast, a low TOF value was observed with 1d, which is presumably related to its steric hindrance effect.…”