Primary amine coupling on nanocarbon catalysts: Reaction mechanism and kinetics via fluorescence probe analysis

Non-metallic nanocarbon materials catalyzed coupling reactions of primary amines to produce imine is an efficient, green and sustainable synthetic route, which has a wide application prospect in fine chemicals or pharmaceutical molecules. In the present study, we show firstly the relatively high catalytic activity of graphene oxide in the reaction of oxidative coupling of benzylamine (OCB), which is even comparable with typical metal-based catalysts, indicating the great potential of nanocarbon materials in this reaction system. More importantly, a novel two-photon fluorescence probe molecule (N-propyl-4-hydrazinyl-1, 8-naphthalimide, NA) with special chemical structure of hydrazine functionality was synthesized. The probe NA could selectively react with aldehyde or ketone compounds, leading to the photoluminescence enhancement via inhibition of photo induced electron transfer (PET) process. The synthesized NA was applied as probe in carbon catalyzed OCB system to predict the existence of reaction intermediate benzaldehyde (BA), indicating the reaction pathway of oxidation-deamination-condensation in nanocarbon catalyzed OCB process. The proposed luminescence-probe strategy for revealing the kinetics and mechanism may also shed light in other reaction systems concerning the intermediates or products of ketones or aldehydes.