Enhancing β-hydroxy ketone selectivity in the aldol condensation of furfural and acetone over N-B-O sites in calcined boron nitride

• Published in: Green chemistry : an international journal and green chemistry resource : GC Vol. 24; no. 18; pp. 686 - 6866
• Main Authors: Deng, Tianyu, Yan, Binhang
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 20.09.2022
• Subjects: Acetone; Air temperature; Alcohols; Aldehydes; Boron; Boron nitride; Condensates; Dehydration; Furfural; Green chemistry; High temperature; Ketones; Lewis acid; Nitrogen; Nitrogen defects; Roasting; Selectivity
• ISSN: 1463-9262; 1463-9270
• DOI: 10.1039/d2gc02243e

Controlling aldol condensation while suppressing dehydration to afford β-hydroxy ketones is a potential and promising synthetic method for obtaining chiral alcohols. However, this strategy only works well in homogeneous processes, and further dehydration of the β-hydroxy ketone occurs irrepressibly in most heterogeneous systems. In this work, intrinsically inert BN calcined at a high temperature in air was found to be able to catalyze the aldol condensation of biomass-derived furfural and acetone to obtain hydrated 4-(furan-2-yl)-4-hydroxybutan-2-one (FAc-OH) with a high selectivity. Two types of oxygen-substituted nitrogen defect sites over air-calcined BN were convincingly identified and successfully correlated with the corresponding catalytic performance for aldol condensation with and without dehydration. A B-centered Lewis acid-catalyzed mechanism was proposed, where the N-B-O sites can selectively produce the β-hydroxy ketone for aldol condensation and the β-hydroxy ketone is more likely to further dehydrate at the O-B-O sites. The controlled synthesis of the two distinct active sites offers an efficient way to switch the distribution of dehydrated and hydrated products produced by aldol condensation. Air-calcined BN can catalyze the aldol reaction of furfural and acetone while suppressing dehydration to afford β-hydroxy ketone. Two types of O-substituted N defect sites were identified and a B-centered Lewis acid-catalyzed mechanism was proposed.