Highly crystalline poly(heptazine imides) by mechanochemical synthesis for photooxidation of various organic substrates using an intriguing electron acceptor - Elemental sulfur

Low-defect potassium poly(heptazine imide) (PHIK-BM) was engineered for application in photocatalytic' oxidation of organic substrates. Mechanochemical pretreatment of a mixture of 5-aminotetrazole in LiCl/KCI eutectics using high-energy ball milling afforded a highly homogeneous mixture that, upon sequential thermolysis at 600 degrees C, gave nanosized particles of PHIK-BM. The photocatalytic activity of the free-standing PHIK-BM plates was assessed in the oxidation of benzyl alcohol to benzaldehyde under visible light irradiation using elemental sulfur as an electron acceptor. Both quantitative conversion (>99%) of benzyl alcohol and selectivity (>98%) with respect to benzaldehyde were achieved. The developed method was extended to aliphatic alcohol oxidation coupled with multicomponent Hantzsch 1,4-dihydropyridine synthesis. These 1,4-dihydropyridines were also photocatalytically oxidized by PHIK-BM to the corresponding substituted pyridines, with very good yields and under mild metal-free conditions. (C) 2017 Elsevier Inc. All rights reserved.