On a novel synthesis of 2-sulfonatobenzoic acid by oxidation of thiosalicylic acid catalyzed by copper(II): a structural study

The oxidation of thiosalicylic acid in methanol into 2-sulfonatobenzoic acid was successfully achieved by the reaction with pyridine-N-oxide in aerobic media containing a copper(II) catalysts. The 100 K structure of the tetraphenylphosphonium 2-sulfonatobenzoic acid [P(C6H5)(4)]C(6)H(4)So(3)COOH (1) has been determined by X ray diffraction methods. The anion shows a novel conformation with a strong intramolecular COOH...OSO2 bond. The oxidation reaction also produces [P(C6H5)(4)](2)[Cu2Cl6] (II), as assessed by single crystal X-ray measurements. When water is added to the reaction medium, the compound I is reformed. Nevertheless, instead of compound 11, chloro tetrapyridine-N-oxide copper(H) chloride monohydrate [Cu(C5H5NO)(4)Cl]Cl . H2O (III) is obtained. The crystal structure of this new copper complex has been determined and is also reported here. The copper ion is in a CuO4Cl pyramidal coordination with the oxygen atoms of four C5H5NO ligands at the square basis (average Cu-O distance of 1.98(l) Angstrom) and a chlorine ion (d(Cu-Cl) = 2.4585(4) Angstrom) at the pyramid apex, Vibrational studies of the three compounds have been performed. Compound III has also been characterized by diffuse reflectance and UV-vis spectroscopy and by its thermal and magnetic behavior.