Microwave-Assisted Synthesis of Amine-Bridged Covalent Triazine Frameworks: Base Selection as the Critical Determinant of Porosity and Network Formation

Covalent triazine frameworks (CTFs) are nitrogen-rich porous polymer networks built from 1,3,5-triazine rings and covalent organic linkers. Their high thermal stability, tunable surface chemistry, and heteroatom-rich structure make them attractive for catalysis, gas adsorption, and separation. A convenient route to amine-bridged CTFs is nucleophilic substitution between cyanuric chloride and polyfunctional amines. The reaction could be conducted by conventional heating; however, commonly it is a long process that requires efficient neutralization of HCl forming during framework growth¹.

Microwave irradiation offers rapid and uniform heating, accelerating triazine-network formation under milder conditions². In this work, microwave-assisted synthesis was evaluated for two CTF families: melamine-derived and p-phenylenediamine-bridged triazine networks. The key variable was the HCl scavenger: for this purpose an inorganic (KOH) and organic (N,N’-diisopropylethylamine, DIPEA) bases were compared.

Melamine–cyanuric chloride coupling in DMSO with KOH under conventional heating (150 °C, 72 h) afforded the framework in 31% yield, whereas microwave irradiation for 1 h doubled the yield. The use of DIPEA in this reaction failed to afford a solid product. Moreover, the microwave-assisted reaction between p-phenylenediamine and cyanuric chloride in presence of KOH resulted in near-complete conversion to corresponding CTF with an unexpectedly high BET surface area¹ (191 m²/g). When DIPEA used in this reaction to quench HCl, the product was found to be practically non-porous.

These examples demonstrate that the selection of HCl scavenger is crucial for substitution reaction efficiency and accessible porosity of resulting frameworks.

References:

¹Peter et al.; https://doi.org/10.1039/D4MA00739E.

²Chaudhary et al.; https://doi.org/10.1039/C8NJ02174K.