α-aminonitriles synthesis and kinetic investigation via photooxidative cyanation of amines in a visible LED-based photomicroreactor

Abstract

α-aminonitriles (AN) are valuable intermediates and building blocks with versatile applications in organic synthesis. Herein, we presented a visible LED-based photomicroreactor for the AN synthesis with three amine substrates, i.e., dibenzylamine (DBA), pyrrolidine (PYR) and piperidiene (PIP), using meso‑tetraphenylporphyrin (m-TPP) and trimethylsilyl cyanide (TMSCN) as photosensitizer and cyanide source, respectively. The results showed that the photooxidative cyanation is a chromoselective and wavelength-selective photochemical transformation with the optimum AN yield and selectivity of 98.2% and 99.5% at a residence time of 2.69 min. Computational studies indicated that a high energy gap between the molecular orbitals of PYP, PIR and their imine intermediates potentially led to their higher reactivity than DBA and formation of by-products with larger molecular weight. Kinetic investigation showed that the apparent rate constants of the DBA photooxidative cyantaion were improved by rising the LED input power, and the applied photosensitizer exhibited high photostability. The overall photonic efficiency of this photomicroreactor was found to be 54.3% within the wavelength range of 400–440 nm, which is higher than previously used photoreactors. Finally, linear correlations were developed between the input power of LED and apparent rate constants of DBA photooxidative cyanation, which would be beneficial for the design, optimization, and scale-up of this photochemical process.