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Benzimidazole and their derivatives are of interest due to their great therapeutic index. 2-Substituted benzimidazoles were synthesized using Philips condensation(1) by refluxing o-phenylendiamine with carboxylic acid (formic acid, acetic acid, propanoic acid and lactic acid) in presence of conc. HCl. Benzimidazoles 1a-d thus obtained were subjected to aminomethylation reaction with formaldehyde and secondary amines (morpholine/Nmethylpiperazine) to give target Mannich bases, that is 2- substituted [(morpholin-4-yl/4-methylpiperazin-1-yl)methyl]-1H-benzimidazoles 3a-h. Characterization of synthesized Mannich bases is based on analytical and spectral studies. Synthesized compounds have also been screened for their antimicrobial activities.