About author :
Department of Pharmaceutical Chemistry
JNTUA – OTRI, Anantapur, India
The benzimidazole contains a phenyl ring fused to an imidazole ring, as indicated in the structure of benzimidazole. Diversity of biological response profile has attracted considerable interest of several researchers across the globe to explore thisskeleton for its assorted therapeutic significance.
1.Synthesis of 2-mercapto benzimidazole
A mixture of 10.8gm (0.1mol) of o-phenylenediamine, 5.65 gm (0.1mol) of potassium hydroxide and 7.67 gm (0.1mole, 6.19ml) of carbon disulfide, 100ml of 95% ethanol and 15 ml of water was taken in a 500ml round bottom flask heated under reflux for three hours. Then 1-1.5 gm of charcoal was added cautiously and the mixture is further heated at the reflux for 10 minutes, the charcoal is removed by filtration. The filtrate is heated to 60-70oC, 100ml of warm water is added, and acidified with dilute acetic acid with good stirring. The product separated as glistening white crystals, and the mixture is placed in a refrigerator for three hours to complete the crystallization. The product is collected on a Buckner funnel and dried over night at 40oc. The dried product is recrystallised by ethanol the yield is 8.5gm (73%) melting point is 300-305oC .
2. Synthesis of ethyl (1H-benzimidazol-2-yl-sulfanyl) acetate
A stirred mixture containing 4.5gm of (0.03mol) of 2-mercaptobenzimidazole, 60ml of ethanol and 1.68gm of (0.03mol) potassium hydroxide was added and heated at 78-80oC for 10-minutes. Then ethyl chloro acetate (3.66ml, 0.03mol) was added in one portion, an exothermic reaction set in causing a temperature rise from 30-40oC. After stirring at 25-300c for 18-hours, the reaction mixture was added to 100gm of ice-water and stirred for 30-minutes at 0-100C. The precipitate was collected by filtration washed with water until free of chloride and air dried at 500c and recrystallised by water the yield is 6 gm (62.25%). melting point is 1050C.
3.Synthesis of 2-(1H-benzimidazol-2-ylsulfanyl) acetohydrazide
The mixture of 2-carboxy ethyl thio 1H-benzimidazole 4gm (0.004mole) and hydrazine hydrate 6ml (0.01mole) are mixed well in a RBF and heated on water bath for 10 min. then dissolved in 60 ml ethanol, the reaction mixture is heated with reflux the reaction mixture is heated with reflux condenser for six hours, cooled to room temperature and the reaction mixture was added to 100gm of ice-water, and kept aside for the crystallization. The colorless crystals are collected by filtration, and recrystallized from water. Melting point is 180-1850C; the yield is 60-70% .
4.General procedure for the preparation of schiff bases compound
A equimolar solution of carboxyl hydrazide (0.009 mol, 2gm) is dissolved in 10ml of ethanol and to this solution substituted aldehydes in equimolar qty (0.009mol, 0.917) is added with 4-6 drops of glacial acetic acid was added, this reaction mixture is kept under reflux for 8 hours. After cooling to room temperature was added to cold water. Compound gets separated as solidfiltered, dried and recrystalized with chloroform.
The present study explains the synthesis and characterization of benzimidazol derivative i.e., 2-[1H- benzimidazole-2yl-sulfanyl]N-[(E)-(4-methoxy phenyl) methylidene] acetohydrazide. At present studies find the structural-activity relationship (SAR) and to optimize the structure. The synthesized benzimidazol derivative characterized by IR, 1H NMR spectral data analysis. The purity of the synthesized benzimidazol derivative was checked by (TLC) thin layer chromatography and Rf value was recorded.
Key words: Benzimidazole, Furan, Acetohydrazide, Imidazole, n-Hexane, Ethyl acetate, Chloroform, Methanol