Synthesis and Antimicrobial Activity of Some New Formazan Derivatives

A series of new substituted formazan derivatives has been synthesized from corresponding aryl diazonium chloride and Schiff base in pyridine. The synthesized compounds were identified by spectral studies and screened for their antimicrobial activities.

Piperazine derivatives have also shown to possess diverse biological properties such as anti-histamine, antikatonic, anticonvulsant, antibacterial 14 and as potential cocaineabuse therapeutic agents 15 .Piperazine possesses dopamine receptor activating property.The two nitrogen of the piperazine molecule are present in a rigid conformational structure that probably favours their involvement to the dopamine receptors 16 .In the present study we have synthesized ten substituted formazan derivatives (3a-j) by coupling Schiff base with appropriate aryl diazonium chlorides in pyridine.(Scheme 1) The structures of these derivatives were assigned on the basis of elemental analysis, IR and 1 H NMR spectral data.The synthesized compounds were screened for their antimicrobial activities.

Experimental
Melting points were determined in open capillary tubes and are uncorrected.IR spectra were recorded in KBr on a Shimadzu 8400S FTIR spectrophotometer. 1 H NMR spectra were recorded on a Hitachi 300MHz using TMS as an internal standard and elemental analysis had been carried out on Perkin-Elmer CHNS-2400.

General procedure for the preparation of formazans Preparation of 4-(4-ethylpiperazin-1-yl) benzenamine (1)
A mixture of N-ethylpiperazine (0.1 mol) and p-chloroaniline (0.1 mol) and anhydrous K 2 CO 3 in absolute alcohol (20 mL) was refluxed for 4 h.The resultant mixture was cooled to room temperature and poured into ice-cold water with stirring.The separated solid was filtered, washed with water and recrystallized from ethanol.

Preparation of N-(Substituted phenylimino)-N'-(4-(4-ethylpiperazin-1-yl) phenyl) benzamidine (Formazans) (3a-j)
A cold stirred solution of aniline (0.01 mol) previously dissolved in aqueous HCl (10 mL) was diazotized over crushed ice by dropwise addition of cold aqueous solution of NaNO 2 (2.5 g) with stirring till a clear solution of diazonium salt of respective amine was obtained.The temperature 17 was at 0-5 o C. It was further stirred until the positive test of nitrous acid on starch-iodide paper was obtained.This mixture was then poured into a cold solution of N-Benzylidene-4-(4-ethylpiperazin-1-yl) benzenamine (0.01 mol) dissolved in dry pyridine (5.0 mL).The reaction mixture was further stirred for 2 h maintaining temperature 0-5 o C. The mixture was then poured into water with continuous stirring.The resultant dark coloured mass was filtered and washed with water till free from pyridine, dried and recrystallized from ethanol.
The spectral data of the synthesized compounds 3a-j are given below.

Antimicrobial activity
The synthesized compounds 3a-3j were screened for their antibacterial activity against B. Subtilis, S. Typhi and E. Coli and antifungal activity against C.albicans at a concentration of 40 µg/mL in DMF by cup-plate method 18,19 .Standard anti-bacterial and antifungal drug, gentamycin and miconazole respectively were also tested under similar conditions for comparison.Zone of inhibition in mm of synthesized compounds and standard drugs are shown in Table 1.

Conclusion
Most of the synthesized compounds have shown antibacterial activity to some extent.Among the synthesized compounds, compound 3f shows good activity, while 3d, 3a, 3g, 3e, 3j, 3c and 3h shows moderate activity.The other two compounds 3b and 3i show feeble activity against E. coli.Against B. subtilis the compound 3c shows good activity, while compounds 3f, 3a, 3j, 3e and 3d show moderate to feeble activity.The remaining compounds 3b, 3i, 3g and 3h have been found to be inactive against B. subtilis.The compound 3j shows good activity, while compounds 3i, 3f, 3g, 3a, and 3h show moderate activity against S. typhi.Compounds 3d and 3e have been found to be inactive against S. typhi.The compounds 3c and 3g show good activity while the remaining compounds 3b, 3d, 3f, 3e, 3j, 3a, 3i and 3h show moderate to good activity against C. albicans