On a Novel Synthesis of 2-Sulfonatobenzoic Acid by Oxidation of Thiosalicylic Acid Catalyzed by Copper (II): a Structural Study,

E. G. FERRER; P. A. M. W ILLIAMS; E.E.CASTELLANO; O.E.PIRO

ZEITSCHRIFT FUR ANORGANISCHE UND ALLGEMEINE CHEMIE

Año: 2002 vol. 628 p. 1978 - 1984

0044-2313

Abstract. 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-sulfonatebenzoic acid [P(C6H5)4]C6H4SO3COOH (I) 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 II, chloro tetrapyridine-N-oxide copper(II) chloride monohydrate [Cu(C5H5NO)4Cl]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(1) A ° ) and a chlorine ion (d(Cu_Cl) _ 2.4585(4) A ° ) 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.