Photocatalytic application of carbon dots in the knoevenagel condensation. a mass spectrometric study

The Knoevenagel condensation is a variation of the aldol condensation between an active methylene compound and a carbonyl compound (aldehyde or ketone). This reaction has been widely used in the synthesis of various chemical compounds, including natural products, polymers, cosmetics, and drugs. The Knoevenagel condensation was typically catalysed by bases although the use of alternative green catalysts has been explored [1]. For this purpose, carbon dots (CDs) obtained from biowastes represents good candidates as catalysts [2]. The present study examined the photocatalytic application of CDs in the Knoevenagel condensation. The p-anisaldehyde was reacted with different methylene-activated compounds and the reaction was dual-mode monitored by electrospray ionization mass spectrometry (ESI-MS) in the presence of an UV irradiation source (365 nm, 9 Watt) to capture the ionic reactants, intermediates, and products of the reaction. Different reaction intermediates were intercepted based on the methylene-activated compounds used. Two different mechanisms were proposed: a classic base-catalyzed pathway passing through the formation of an aldol intermediate and an UV-promoted radical route resulting from a hydrogen atom abstraction from the C2-H moiety of the methylene group [3].