thiourea and chlorite

Allylthiourea (ATU) and chlorate (ClO

Topics: Ammonium Compounds; Chlorates; Chlorides; Filtration; Nitrification; Research; Thiourea; Water Purification

The reaction between tetramethylthiourea (TTTU) and slightly acidic chlorite has been studied. The reaction is much faster than comparable oxidations of the parent thiourea compound as well as other substituted thioureas. The stoichiometry of the reaction in excess oxidant showed a complete desulfurization of the thiocarbamide to yield the corresponding urea and sulfate: 2ClO2(-) + (Me2N)2C ═ S + H2O → (Me2N)2C ═ O + SO4(2-) + 2Cl(-) + 2H(+). The reaction mechanism is unique in that the most stable metabolite before formation of the corresponding urea is the S-oxide. This is one of the rare occasions in which a low-molecular-weight S-oxide has been stabilized without the aid of large steric groups. ESI-MS data show almost quantitative formation of the S-oxide and negligible formation of the sulfinic and sulfonic acids. TTTU, in contrast to other substituted thioureas, can only stabilize intermediate oxoacids, before formation of sulfate, in the form of zwitterions. With a stoichiometric excess of TTTU over oxidant, the TTTU dimer is the predominant product. Chlorine dioxide, which is formed from the reaction of excess chlorite and HOCl, is a very important reactant in the overall mechanism. It reacts rapidly with TTTU to reform ClO2(-). Oxidation of TTTU by chlorite has a complex dependence on acid as a result of chlorous acid dissociation and protonation of the thiol group on TTTU in high-acid conditions, which renders the thiol center a less effective nucleophile.

Topics: Catalysis; Chlorides; Chlorine Compounds; Drug Combinations; Free Radicals; Ions; Kinetics; Molecular Structure; Oils; Oxidation-Reduction; Oxides; Phenols; Spectrum Analysis; Thiourea; Ultraviolet Rays; Water

Precise spatio-temporal organization of chemical, hydrodynamic, and mechanical processes is typical for biological systems where particular chemical reactions have to accrue in precisely assignment place and time. It is rarely studied and observed in chemical systems. We report unusual precipitation pattern formation of PbSO(4) in chemical media (Pb(2+)-Chlorite-Thiourea System). We have found that there is a region in a plane of initial concentrations of chlorite ions and thiourea where precipitation of lead sulfate appears in a form of ring if a pellet of lead nitrate is placed into the system. The whole process may be divided into three stages: movement of first circular front of lead containing solution, formation of a ringlike pattern of lead sulfate, and finally, propagation of this pattern resulting in a formation of ring with final inside diameter. Our experiments indicate that the following values are reproducible and quantify the PbSO(4) ring evolution: induction time, radius of the ring birth, speed of ring propagation toward the center, and final inside radius of the ring. Numerical solution of kinetic equations allowed us to give a qualitative explanation for the phenomenon observed. Formation and evolution of the PbSO(4) rings are caused by interplay of concentration gradients in the system and chemical reactions that occur in excitable chlorite-thiourea system. Chemical reactions and hydrodynamic processes form a complex causal network that made morphogenesis of this unusual pattern possible.

Topics: Chlorides; Hydrodynamics; Lead; Spatio-Temporal Analysis; Thiourea

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