Preparation, characterization, and use of poly(vinylpyrrolidonium) hydrogen phosphate ([PVP-H]H2PO4) as a new heterogeneous catalyst for efficient synthesis of 2-amino-tetrahydro-4H-pyrans

A novel Bronsted solid acid named poly(vinylpyrrolidonium) hydrogen phosphate ([PVP-H]H2PO4) has been prepared by using H3PO4 and poly(vinylpyrrolidone) as green and commercially available reagents. The prepared reagent was characterized using a series of techniques including Fourier-transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, energy-dispersive X-ray analysis (EDAX), pH analysis, and Hammett acidity function. The mentioned solid acid with wide acidic functional group sites can be utilized as a highly efficient, heterogeneous, and reusable catalyst for preparation of 2-amino-3-cyano-5-oxo-5,6,7,8-tetrahydro-4H-benzopyrans using aldehydes, dimedone, and malononitrile. Also, this catalyst can be reused for several times without loss of catalytic activity.