title: Oxidation and chemiluminescence of catechol by hydrogen peroxide in the presence of Co(II) ions and CTAB micelles.
abstract: The oxidation of catechol in neutral and slightly alkaline aqueous solutions (pH 7-9.6) by excess hydrogen peroxide (0.002-0.09 mol/L) in the presence of Co(II) (2.10(-7)-2.10(-5) mol/L) is accompanied by abrupt formation of red purple colouration, which is subsequently decolourized within 1 h. The electron spectra of the reaction mixture are characterized by a broad band covering the whole visible range (400-700 nm), with maximum at 485 nm. The reaction is initiated by catechol oxidation to its semiquinone radical and further to 1,2-benzoquinone. By nucleophilic addition of hydrogen peroxide into the p-position of benzoquinone C=O groups, hydroperoxide intermediates are formed, which decompose to hydroxylated 1,4-benzoquinones. It was confirmed by MS spectroscopy that monohydroxy-, dihydroxy- and tetrahydroxy-1,4-benzoquinone are formed as intermediate products. As final products of catechol decomposition, muconic acid, its hydroxy- and dihydroxy-derivatives and crotonic acid were identified. In the micellar environment of hexadecyltrimethylammonium bromide the decomposition rate of catechol is three times faster, due to micellar catalysis, and is accompanied by chemiluminescence (CL) emission, with maxima at 500 and 640 nm and a quantum yield of 1 x 10(-4). The CL of catechol can be further sensitized by a factor of 8 (maximum) with the aid of intramicellar energy transfer to fluorescein.
authors.affiliation: Department of Physical Chemistry, Palacký University, Faculty of Science, tr. Svobody 26, 771 46 Olomouc, Czech Republic. lasovsky@prfnw.upol.cz
authors.forename: Jan
authors.initials: J
authors.lastname: Lasovsky
authors.forename: Jan
authors.initials: J
authors.lastname: Hrbac
authors.forename: Dana
authors.initials: D
authors.lastname: Sichertova
authors.forename: Petr
authors.initials: P
authors.lastname: Bednar
mesh_terms: D002396:Catechols / Q000138:chemical synthesis / Q000737:chemistry*; D000077286:Cetrimonium; D002593:Cetrimonium Compounds / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000737:chemistry; D008163:Luminescent Measurements / Q000295:instrumentation / Q000379:methods*; D013058:Mass Spectrometry / Q000379:methods; D008823:Micelles; D010084:Oxidation-Reduction; D012680:Sensitivity and Specificity; D012996:Solutions / Q000737:chemistry; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D002396:Catechols; D002593:Cetrimonium Compounds; D007477:Ions; D008823:Micelles; D012996:Solutions; D014867:Water; D003035:Cobalt; D006861:Hydrogen Peroxide; C034221:catechol; D000077286:Cetrimonium