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The hydroxyl radical ( Á OH)-mediated oxidation of two simple textile azo dyes, methyl orange and calmagite, was studied by the pulse radiolysis technique. The oxidation of methyl orange and calmagite by hydroxyl radicals was extremely fast, with second-order rate constants of (2.0 AE 0.3) Â 10 10 and (1.1 AE 0.2) Â 10 10 l mol, respectively, at 25°C and pH 9.2. The transient intermediates formed by the interaction of hydroxyl radical with the dyes displayed absorption bands at 300, 480 and 720 nm for calmagite and 360 and 580 nm for methyl orange. These transients decompose by first-order kinetics with half-lives of 150-200 ms. In the case of methyl orange, hydroxyl radical reacts by one-electron oxidation at the nitrogen center, forming the anilino cation radical. This was confirmed by comparing the absorption spectrum of the intermediate formed by the interaction of Á OH with methyl orange and that obtained by the reaction between a one-electron oxidant such as carbonate radical (CO 3 ÀÁ ) and methyl orange. Hydroxyl radicals react with calmagite by addition to the benzene ring, producing hydroxycyclohexadienyl radicals, which rapidly decompose to phenoxyl-type radicals by water elimination.

Oxidative degradation process of organic materials in wastewater is an area of significant current interest. In the case of commercial textile dyes, little is known about the structures of the actual products that can form once a dye has been submitted to oxidative conditions. Here, a product analysis approach was applied to identify some of the major early degradation products of Uniblue A (UBA) when reacted with peroxydisulfate (PDS). UBA is the vinyl sulfone form and major wastewater constituent of the commercial anthraquinone textile dye C.I. Reactive Blue 19. Using NMR, LC-MS, and Raman, four reaction products could be identified, and possible reaction pathways are discussed.

The use of carbodiimides to create an amine-reactive reagent is a favored means of modifying proteins, nucleic acids, and small-molecule organic compounds containing carboxylic acid groups, or vice versa. The rules for optimizing the amidation have not previously been presented quantitatively, but such optimization is critical when modifying with an expensive fluorescent dye. In this study, the reaction conditions for attaching an amine-containing dye to sodium carboxymethyl cellulose (NaCMC) via 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDAC) are systematically examined, with an emphasis on the role played by the pK a of the coupling amine group. The reactivity is reasoned to be proportional to the product of the fractional deprotonation of NaCMC, the fractional protonation of the carbodiimide, the fractional deprotonation of the amine-containing dye, and the relative stability of the reactants and intermediates: (αCMC‑)(1 – αEDAC)(αamine)S f. The pH dependence of this product for a given amine group pK a can be used, by comparison to experimental data, to determine the pH dependence of S f. Substitution of the pK a for a second amine-containing dye and inverting the above procedure gives a semiquantitative prediction of the pH conditions to optimize its amidation. The results suggest that generally available pK a values and the above form of S f can be used to optimize carbodiimide assisted amidation.