Synthesis of New Bis-1,2,4-triazole Derivatives

A series of new


Scheme
Cl In the IR spectra of compounds 4 the characteristic C=N absorption bands appeared at 1597 cm -1 . The 1 H-NMR signals for the -N=CH group were observed at δ 8.23-8.70 ppm. The 13 C-NMR signals for the -N=CH-group were recorded at δ 164 ppm. Reduced compounds 5 showed IR absorption bands around 3245-3290 cm -1 (υ NH ). The 1 H-NMR signals for the -NH-CH 2 -group of these compounds were observed as a doublet or strong singlet at around δ 3.55-3.75 ppm and the proton signals of -NH-CH 2 -groups were recorded as a triplet or strong singlet between δ 6.95-7.08 ppm. The NH-CH 2 -carbon signals of compounds 5 were recorded at δ 48 ppm in the 13 C-NMR. In addition to this, in the 13 C-NMR the triazole C3 and C5 of the bis-Schiff base derivatives 4 were observed between δ 148-149 ppm and the triazole C3 and C5 signals of the reduced compounds 5 were observed between δ 152-153 ppm.

General
Melting points were determined on a Barnstead Electrothermal melting point apparatus and are uncorrected. 1 H-NMR and 13 C-NMR spectra (δ, ppm) were recorded on a Varian-Mercury 200 MHz spectrophotometer using tetramethylsilane as the internal reference. The IR spectra (υ, cm -1 ) were obtained with a Perkin-Elmer 1600 FTIR spectrometer in KBr pellets. The mass spectra were recorded on a MicroMass Quattro LC-MS/MS (70 eV) spectrometer. The necessary chemicals were purchased from Merck and Fluka.

Synthesis of bis-aldehydes 1a-b
Salicylaldehyde (0.01 mol) was dissolved in hot ethanolic KOH (prepared by dissolving 0.01 mol of KOH in 100 mL of absolute ethanol) and the solvent was then removed in vacuo. The residue was dissolved in DMF (25 mL) and the appropriate dihalide (0.005 mol) was added. The reaction mixture was refluxed for 5 minutes, during which KCl separated out. The solvent was then removed in vacuo and the remaining material was washed with water and crystallized from an appropriate solvent to give compounds 1a-b.

Synthesis of hydrazones 2a-c
A solution of an appropriate hydrazide (0.01 mol) in absolute ethanol (25 mL) was added to a solution of iminoester hydrochloride (0.01 mol) in absolute ethanol (25 mL). The mixture was stirred for 6 h at 0-5 °C and subsequently for 2 h at room temperature. The reaction mixture was then poured into a beaker containing cold water (40 mL) and ice (10 g). The precipitate formed was washed with ice-water (50 mL), dried and the product was recrystallized from from 2:1 benzene-petroleum ether to give compounds 2a-c.

Synthesis of amino compounds 3a-c
Compounds 2 (0.005 mol) were added to a solution of hydrazine hydrate (0.01 mol) in 1-propanol (50 mL) and the mixture was refluxed for 24 h. On cooling, a precipitate was formed. This product was filtered and, after drying, was washed with benzene (20 mL). The product was then recrystallized from an appropriate solvent to give compounds 3a-c.

Synthesis of bis-Schiff bases 4a-f
The corresponding bis-aldehyde (0.01 mol) was added to a solution of compound 3 (0.005 mol) in glacial acetic acid (20 mL) and the mixture was refluxed for 16 h. After cooling, the mixture was poured into a beaker containing ice-water (100 mL). The precipitate formed was filtered. After drying in vacuo, the product was recrystallized from 1:2 benzene-petroleum ether to give the desired compound.

Synthesis of reduced rompounds 5a-f
The corresponding compound 4a-f (0.005 mol) was dissolved in dried methanol (50 mL) and NaBH 4 (0.01 mol) was added in small portions to this solution. The mixture was refluxed for 20 min and then allowed to cool. After evaporation at 30-35 °C under reduced pressure, the solid residue was washed with cold water. After drying in vacuo, the solid product was recrystallized from an appropriate solvent (1:1 ethanol-water, unless otherwise noted) to afford the desired compound.