Synthesis, characterization and application of magnetic biochar sulfonic acid as a highly efficient recyclable catalyst for preparation of spiro-pyrazolo[3,4-b]pyridines

A magnetic biochar sulfonic acid was prepared and characterized by fourier infrared spectroscopy (FT-IR), powder x-ray diffraction technology, scanning electron microscope, transmission electron microscope and vibrating sample magnetometer techniques. The prepared catalyst exhibited excellent catalytic activity for synthesis of spiro-pyrazolo[3,4- b ]pyridine derivatives via one-pot three-component reaction of 1 H -pyrazol-5-amine, isatin and 3-oxo-3-phenylpropanenitrile. The catalyst could be readily recovered and reused several times without an obvious decay of catalytic performance.