The carboxylic acid termination of the single-walled carbon nanotubes (SWNTs) provides a convenient link for covalent bonding between the SWNTs and polymer or biological systems. In this work, two approaches for covalent attachment of carboxylic acid groups to the side-walls of single walled carbon nanotubes are presented. Both protocols are based on chemical manipulation of benzonitrile residues, easily introduced onto the SWNTs by in situ diazonium salt formation of 4-aminobenzonitrile. In the first approach, benzonitrile groups on SWNTs were treated with aq. NaOH solution to form benzoic acid moieties. The second approach on benzonitrile groups is leaded to the formation of benzothiomorpholides via Willgerodt-Kindler reaction which is then converted to benzoic acid moieties on SWNTs. Moreover, a simple one-pot entry into the formation of benzoic acid moieties is presented. SWNTs were characterized by a set of methods including FT-IR, UV/vis, TGA, SEM and Raman techniques. The presence of thioamide groups on SWNT is also proved directly by XPS spectroscopy. (C) 2012 Elsevier B.V. All rights reserved.