Construction of Crystalline 2D Covalent Organic Frameworks with Remarkable Chemical (Acid/Base) Stability via a Combined Reversible and Irreversible Route

Two
new chemically stable [acid and base] 2D crystalline covalent
organic frameworks (COFs) (TpPa-1 and TpPa-2) were synthesized using combined reversible and irreversible organic
reactions. Syntheses of these COFs were done by the Schiff base reactions
of 1,3,5-triformylphloroglucinol (Tp) with p-phenylenediamine (Pa-1) and 2,5-dimethyl-p-phenylenediamine (Pa-2), respectively, in 1:1 mesitylene/dioxane.
The expected enol–imine (OH) form underwent irreversible proton
tautomerism, and only the keto–enamine form was observed. Because
of the irreversible nature of the total reaction and the absence of
an imine bond in the system, TpPa-1 and TpPa-2 showed strong resistance toward acid (9 N HCl) and boiling water.
Moreover, TpPa-2 showed exceptional stability in base
(9 N NaOH) as well.