Preparation, characterization, and application of supported phosphate acid on the UiO-66-NH2 as an efficient and bifunctional catalyst for the synthesis of acridines

Most metal-organic frameworks (MOFs) as heterogeneous catalytic systems limit their use in the catalytic process due to a lack of active functional sites. In this study, the novel modification of the Zr-MOF, UiO-66-NH2 was studied. Initially, UiO-66-NH2 was modified with 3,4 dihydroxybenzaldehyde to the creation of hydroxyl groups and subsequently reacts with di-n-butyl phosphate. The supported phosphate acid named UiO-66-N=CH-C6H3PO4H is introduced as a green, efficient, acidic-basic nanocatalyst. The structural and textural properties of the prepared UiO-66-N=CH-C6H3PO4H nanocatalyst were characterized by several techniques such as FTIR, XRD, FE-SEM, EDX, SEM elemental mapping, N-2 adsorption-desorption, and TGA. Hydrogen phosphate groups on the surface are the main active catalytic sites. The performance of supported phosphate acid was applied for a one-pot, three-component approach to synthesize acridine derivatives using various aldehydes, ammonium acetate, and dimedone. The Bronsted acid and Bronsted base sites in phosphate acid and Lewis acid sites in the MOF were synergistically catalyzed the acridines synthesis. The nanocatalyst has important properties such as durability and robustness which are necessary parameters for the development of a new catalytic system for acid-catalyzed syntheses. This approach offers simple and optimum synthesis conditions, products with high efficiencies in short reaction times, and the ability to recover nanocatalyst for five consecutive cycles without a substantial decrease in catalytic efficiency.

Automated summary

A new metal-organic framework catalyst, UiO-66-N=CH-C6H3PO4H, was studied, which showed hydrogen phosphate groups as the main active catalytic sites on its surface. The catalyst exhibited durability and robustness in acid-catalyzed syntheses, making it a promising candidate for catalytic applications.