Anodic oxidation of the dye materials methylene blue, acid blue 25, reactive blue 2 and reactive blue 15 and the characterisation of novel intermediate compounds in the anodic oxidation of methylene blue

Abstract

Anodic oxidation of the dye molecules, methylene blue, acid blue 25, reactive blue 2 and reactive blue 15 in chloride solution leads to colour destruction but UV and TOC data show that the oxidation reactions do not lead to complete destruction of the organic molecules. Analysis of the anodic oxidation products of [3,7-bis (dimethylamino) phenothiazinium] chloride (methylene blue) in a chloride solution provides evidence for formation of seven neutral and two charged intermediates. The main intermediate is identi®ed by its X-ray diffraction crystal structure and accurate mass spectrometry as the novel leuco dye 4,6-dichloro-7-dimethylamino-3H-phenothiazin-3-one, C 14 H 10 Cl 2 N 2 OS (I) formed by replacement of one of the dimethylamino groups of methylene blue with oxygen accompanied by regiospeci®c chlorination of the carbocyclic systems. The mass spectra of other intermediates formed are interpreted in terms of the structure of I.

Kinetic Study of the Electrochemical Oxidation of Methylene Blue with Pt Electrode

“…Probably redox reaction occurred between the electrolysis product and acetone. [19]. In the present case, the indirect oxidation of MB + did not lead to total mineralization of MB + as in the case with modified TiO 2 electrode [22], and TiRuO 2 [17], but it produces other toxic compounds.…”

“…Chlorine can electrochemically oxidize organic molecules quickly and irreversibly due to its intense oxidative activity. However, gaseous chlorine and hypochlorous acid can be easily interacted with organic molecules to form carcinogenic halogen compounds [19,20]. The efficiency of electrochemical oxidation is a function of electrode materials and supporting medium [14,17,19].…”

“…However, gaseous chlorine and hypochlorous acid can be easily interacted with organic molecules to form carcinogenic halogen compounds [19,20]. The efficiency of electrochemical oxidation is a function of electrode materials and supporting medium [14,17,19]. A brief review about the use of Boron Doped Diamond (BDD) in electrochemical oxidation provides total mineralization with high current efficiency of different organic molecules in real wastewaters [21].…”

“…The indirect oxidation of (MB + ) using chloride resistant mixed oxide metal occurs by replacement of one of dimetylamino groups by oxygen accompanied by chlorination of the aromatic rings [19]. However, using other electrodes such as BDD, PbO 2 /TiO 2 and TiRuO 2 /Ti oxide leads to total mineralization and decolorization of MB + solution [14,17,22].…”

Opportunity to recycle chromium(VI) by in situ electro‐oxidation

“…Effect of chloride ion on in situ electro-oxidation of Cr(III) to Cr(VI) at current 3.0 A and initial pH 5.0 Anodic oxidation 35 is often found to be more efficient in the presence of chloride ions, and for this reason the effects of chloride ion on the in situ electro-oxidation of Cr(III) for different chloride ion concentrations (150, 300 and 500 ppm) were studied. Results are shown in Table 1.…”