Sulfonated nanohydroxyapatite functionalized with 2-aminoethyl dihydrogen phosphate (HAP@AEPH2- SO3H), a new green, recyclable solid acid catalyst, was prepared and characterized using FT-IR, XRD, SEM, TEM and TGA/DTA techniques. The composition of HAP@AEPH2-SO3H was determined as nanohydroxyapatite, while the particles were observed to have nanorod morphology. Size estimations using TEM (10–100 nm) and the crystallinity from XRD (hexagonal phase) are well-matched to the character of nanohydroxyapatite. The catalytic activity of HAP@AEPH2-SO3H was evaluated for the synthesis of 4,40-(aryl methylene)bis(3-methyl-1H-pyrazol-5-ol)s via one-pot reactions of phenylhydrazine/or hydrazine hydrate, ethyl acetoacetate and aldehydes under solvent-free conditions. This catalyst showed notable advantages, such as environmental friendliness, excellent yields, shorter reaction time, reusability of the inexpensive catalyst and easy workup procedure.

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