thiourea and hydrogen-sulfite

Sulfite is a very important species, affecting human health, plant and animal life, and environmental sustainability. In this study, for the first time, an ionophore-based ion-selective optode was constructed for hydrogen sulfite determination in beverages, such as Birell® and Sprite®, water, and soil samples; instead of normal pH-chromoionophores, polyaniline film was precipitated on a glass slide and used for the transduction of the sensation mechanism. The ionophore-modified polyaniline-based optode incorporated thiourea derivative as an ionophore and tridodecyl methyl ammonium chloride as an ion-exchanger. The optode film was prepared

Topics: Humans; Hydrogen-Ion Concentration; Ionophores; Soil; Sulfites; Thiourea; Wastewater

The oxidation reactions of N-acetylthiourea (ACTU) by chlorite and chlorine dioxide were studied in slightly acidic media. The ACTU-ClO(2)(-) reaction has a complex dependence on acid with acid catalysis in pH > 2 followed by acid retardation in higher acid conditions. In excess chlorite conditions the reaction is characterized by a very short induction period followed by a sudden and rapid formation of chlorine dioxide and sulfate. In some ratios of oxidant to reductant mixtures, oligo-oscillatory formation of chlorine dioxide is observed. The stoichiometry of the reaction is 2:1, with a complete desulfurization of the ACTU thiocarbamide to produce the corresponding urea product: 2ClO(2)(-) + CH(3)CONH(NH(2))C=S + H(2)O --> CH(3)CONH(NH(2))C=O + SO(4)(2-) + 2Cl(-) + 2H(+) (A). The reaction of chlorine dioxide and ACTU is extremely rapid and autocatalytic. The stoichiometry of this reaction is 8ClO(2)(aq) + 5CH(3)CONH(NH(2))C=S + 9H(2)O --> 5CH(3)CONH(NH(2))C=O + 5SO(4)(2-) + 8Cl(-) + 18H(+) (B). The ACTU-ClO(2)(-) reaction shows a much stronger HOCl autocatalysis than that which has been observed with other oxychlorine-thiocarbamide reactions. The reaction of chlorine dioxide with ACTU involves the initial formation of an adduct which hydrolyses to eliminate an unstable oxychlorine intermediate HClO(2)(-) which then combines with another ClO(2) molecule to produce and accumulate ClO(2)(-). The oxidation of ACTU involves the successive oxidation of the sulfur center through the sulfenic and sulfinic acids. Oxidation of the sulfinic acid by chlorine dioxide proceeds directly to sulfate bypassing the sulfonic acid. Sulfonic acids are inert to further oxidation and are only oxidized to sulfate via an initial hydrolysis reaction to yield bisulfite, which is then rapidly oxidized. Chlorine dioxide production after the induction period is due to the reaction of the intermediate HOCl species with ClO(2)(-). Oligo-oscillatory behavior arises from the fact that reactions that form ClO(2) are comparable in magnitude to those that consume ClO(2), and hence the assertion of each set of reactions is based on availability of reagents that fuel them. A computer simulation study involving 30 elementary and composite reactions gave a good fit to the induction period observed in the formation of chlorine dioxide and in the autocatalytic consumption of ACTU in its oxidation by ClO(2).

Topics: Catalysis; Chlorides; Chlorine Compounds; Computer Simulation; Halogens; Hydrogen-Ion Concentration; Kinetics; Models, Chemical; Oxidation-Reduction; Oxides; Sulfates; Sulfenic Acids; Sulfhydryl Compounds; Sulfinic Acids; Sulfites; Sulfur; Thiourea; Urea