Hydrazines ultrasonic irradiation

The effect of ultrasonic irradiation on hydrazine reductions in the presence of iron powder and activated carbon in ethanol has also been evaluated. The studies include graphite-catalyzed reductions of aromatic nitro compounds to the corresponding arylamines. The notable features of these reactions are the low cost, high yields and the simplicity of the work-up procedure. Significantly, nitro groups can be reduced in the presence of a variety of functional groups. 

Reactions induced by ultrasonic irradiation of methyl 9,12-dioxostearate with hydrazines in water in the presenee of acidic alumina gave high yields of pyridazine fatty esters directly (95). The synthesis of novel piperidine- [25] and pyridine- [26] containing long-chain fatty ester derivatives has been reported starting from methyl wo-ricinoleate, 9-hydroxy-18 l(12Z) (96). Allylic amination of methyl oleate with bis(A-p-toluenesulfonyl)sulfodiimide gave a mixture of methyl ll-amino-(iV-p-toluenesulfonyl)-18 l(9 ) and methyl 8-amino-(Af-p-toluenesulfonyl)-18 l(9 ) (97). 

A multi-component one-potreaction of ethyl acetoacetate (57), aromatic aldehydes (58), hydrazine (31), and malononitrile (50) in water afforded dihydropyrano[2,3-c] pyrazoles (59) in good yields (79%-95%) under ultrasonic irradiation in relatively short reaction times (15-40 min). In the absence of nltrasound, the products were obtained in comparatively lower yields (70%-86%) and longer reaction times (60-300 min) (Zou et al. 2011). Darandale et al. (2012) reported a simple and practical ultrasound-promoted synthetic protocol for the synthesis of dihydropyrano[2,3-c] pyrazoles (59) nsing sodium bisulfite (NaHSOj) as a green catalyst in solvent-free conditions. The latter method provides the advantage of a shorter reaction time (30 s) and excellent yields (97%-99%) (Scheme 8.19). 

Other Methods. Other reductants like hydrazine, sodium metal, etc. can be used for the reduction of metal ions. Decomposition of metal salts or complexes by heat treatment is sometimes used for synthesis of fine particles as well. In this case the valence of metals in the fine particles should be carefully examined. Recently, irradiation of ultrasonic wave was applied to the synthesis of colloidal dispersions of metal fine particles. 

A 100 mL flask was charged with hydrazine (1 1 mmol), p-keto ester (2 1 mmol), isatin (3 1 mmol) and malononitrile/ethyl cyanoacetate (4 1 mmol) and piperdine (20 mol%, 0.2 mmol) in ethanol (15 mL). The mixture was sonicated in the water bath of an ultrasonic cleaner (power 250 W irradiation frequency 40 kHz) at room temperature (25 30 °C). After the completion of the reaction (monitored by TLC), the resulting precipitate was filtered and washed with ethanol to afford the pure product of spiro[indoline-3,4 -pyrano[2,3-c]pyrazole] 5 as solid in good to excellent yields. Each of the products was characterized by IR, NMR, C-NMR and HRMS studies. 

Ziarati et al. [69] developed the synthesis of compounds with pharmaceutical and biological properties. Thus, 2-aryl-5-methyl-2,3-dihydro-lH-3-pyrazolones (72) were synthesized via a four-component reaction of ethyl acetoac-etate (66), hydrazine (67), aldehyde (69), and p-naphthol (70) in water under ultrasound irradiation with a multiwave ultrasonic generator in the presence of nanoparticles of copper iodide as catalyst, using a simple preparation protocol (Scheme 17). It should be mentioned that the catalyst could be recycled and reused for five times without evidently... 

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