Two efficient and green methods for synthesis of 4,4′-(arylmethylene)bis(1H-pyrazol-5-ols) without use of any catalyst or solvent

Two efficient and green methods for synthesis of 4,4′-(arylmethylene)bis(1H-pyrazol-5-ols) without use of any catalyst or solvent have been developed simply by heating (at 120°C) or microwave irradiation (300 W) of intimate mixtures of 3-methyl-l-phenyl-5-pyrazolone and aldehyde in 2:1 mole ratio.