Electrophilic cyclizations of α,β-alkynic hydrazones by molecular iodine were investigated for the synthesis of 4-iodopyrazoles. α,β-Alkynic hydrazones were readily prepared by the reactions of hydrazines with propargyl aldehydes and ketones. When treated with molecular iodine in the presence of sodium bicarbonate, α,β-alkynic hydrazones underwent electrophilic cyclization to afford 4-iodopyrazoles in good to high yields. Iodocyclization was general for a wide range of α,β-alkynic hydrazones and tolerated the presence of aliphatic, aromatic, heteroaromatic, and ferrocenyl moieties with electron-withdrawing and electron-donating substituents.

The inhibiting effect of four newly synthesised Schiff bases containing pyridyl group was investigated on the corrosion of low carbon steel in 0.1 M hydrochloric acid solution under various conditions by potentiodynamic polarisation method and impedance measurements. The Schiff bases used were 2-All the Schiff bases inhibit corrosion of low carbon steel and their inhibition efficiencies increase with decrease in temperature and increase in concentration. The difference in protection actions of the inhibitors can be attributed to the presence of substituents in the structures that increase or decrease the electron density on the azomethine (-C=N-) group. Polarisation curves indicate that the Schiff bases act as anodic inhibitors. AC impedance and potentiodynamic polarisation measurements reveal that the compounds are adsorbed on the steel surface and the adsorption obeys the Temkin isotherm. Activation parameters (E a , DH*, DS*) for the corrosion of low carbon steel in 0.1 M HCl were calculated and showed that corrosion was much reduced in the presence of inhibitors.

Synthesis of pyrazoles via electrophilic cyclization of α,β-alkynic hydrazones by copper(I) iodide is described. When treated with copper(I) iodide in the presence of triethylamine in refluxing acetonitrile, α,β-alkynic hydrazones, prepared readily from hydrazines and propargyl aldehydes and ketones, undergo electrophilic cyclization to afford pyrazole derivatives in good to excellent yields. The reaction appears to be general for a variety of α,β-alkynic hydrazones and tolerates the presence of aliphatic, aromatic, and ferrocenyl moieties with electron-withdrawing and electron-donating substituents.

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