A new high efficient and green protocol for the preparation of dihydropyrimido [4,5-b]quinolinetrione derivatives using magnetically solid acid catalyst was presented. High performance solid acid catalyst was prepared through a three-step reaction. Firstly, CoFe 2 O 4 nano particles were synthesized using co-precipitation method. In second step, CoFe 2 O 4 nano particles were coated with SiO 2 shell through treatment with tetraethyl orthosilicate (CoFe 2 O 4 @SiO 2 ). Finaly, CoFe 2 O 4 @SiO 2 was modified with polyphosphoric acid (CoFe 2 O 4 @SiO 2 /PPA) in a simple manner. Green reusable catalyst was characterized in details using FTIR, VSM, TEM, FESEM, EDX and used as catalyst for the synthesis of dihydropyrimido[4,5-b]quinolinetrione derivatives.Reaction was performed under ultrasonic irradiation as green, effective and mild conditions and products were achieved in high to excellent yields.Green and eco-friendly conditions, short reaction times with high yield of products in addition to easy workup are some merits of presented method.
KEYWORDSCoFe 2 O 4 @SiO 2 /PPA, dihydropyrimido[4,5-b]quinolinetrione, green chemistry, solid acidic catalyst, ultrasonic irradiation
Sulfonic acid functionalized silica coated cobalt ferrite nanoparticles (CoFe2O4/SiO2−SO3H) was prepared as an efficient solid acid catalyst for the green synthesis of dihydropyrimido[4,5‐b]quinolinetrione derivatives. CoFe2O4 NPs were prepared by co‐precipitation method and then the silica‐coated CoFe2O4 NPs were modified with chlorosulfonic acid. Obtained CoFe2O4/SiO2−SO3H was characterized by thermo gravimetric analysis (TGA), Fourier transform‐infrared spectroscopy (FT‐IR), scanning electron microscope (SEM), energy‐dispersive X‐ray spectroscopy (EDX), X‐ray diffraction (XRD) and vibrating‐sample magnetometer (VSM). The magnetically separable CoFe2O4/SiO2−SO3H was successfully used for the four component reaction of barbituric acid, dimedone, amines (or ammonium acetate) and benzaldehyde derivatives for the synthesis of dihydropyrimido[4,5‐b]quinolinetriones under thermal and ultrasound conditions. The advantages of presented simple protocol are the easily separation of magnetic catalyst from the reaction medium by an external magnet, short reaction times, green reaction conditions in addition to simple workup and high yield of products.
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