Green and\nEfficient Syntheses of a Series of Imine-Connected\nCovalent Organic Frameworks in Acetic Acid Solution

Covalent organic frameworks (COFs) are a new class of\ncrystalline\nporous polymers that have sparked widespread interest due to their\ndiverse topologies and prospective applications in heterogeneous catalysis,\nsewage treatment, fluorescence sensing, proton conduction, and other\ndomains. In this context, imine-connected COFs are currently being\nsynthesized mostly using classic solvothermal techniques, which is\nincompatible with the concept of green chemistry due to the need for\nhigh reaction temperatures (120–180 °C), long reaction\ntimes (3–7 days), and solvents with high toxicity. To address\nthis issue, this study investigated the use of glacial acetic acid\nor acetic acid aqueous solution as a reaction solvent and catalyst\nto prepare triumphantly eight imine-linked COFs, TAPT-BTCA (<b>1</b>), TAPT-TP (<b>2</b>), TAPT-TFPB (<b>3</b>),\nTAPT-TFPT (<b>4</b>), TAPB-BTCA (<b>5</b>), TAPB-TP (<b>6</b>), TAPB-TFPB (<b>7</b>), and TAPB-TFPT (<b>8</b>) by employing amine monomers of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine\n(TAPT) or 1,3,5-tri(4-aminophenyl)benzene (TAPB) to react with aldehyde\nmonomers of 1,3,5-phenyltrialdehyde (BTCA), 1,3,5-tris(4-formylphenyl)benzene\n(TFPB) or 1,3,5-tris(4-formylphenyl)triazine (TFPT), and 2,4,6-triformylphloroglucinol\n(TP), respectively. The approach has numerous advantages including\nshort duration, high yield, low energy consumption, and little solvent\npollution. This considerably reduces the synthesis difficulty and\npromotes the feasibility of subsequent large-scale synthesis. Furthermore,\nin light of the diverse conditions required for the reaction of the\neight different COF materials listed above, we provide explanations\nfrom the standpoint of the reaction mechanism and accumulation energy,\nwhich are useful for manufacturing comparable COFs.