First Advisor

Reuben H. Simoye

Term of Graduation

Spring 2006

Date of Publication

3-1-2006

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.) in Environmental Sciences and Resources: Chemistry

Department

Environmental Sciences and Resources

Language

English

Subjects

Organosulfur compounds, Sulfur compounds, Oxidation-reduction reaction, Dynamics, Nonlinear theories

DOI

10.15760/etd.8095

Physical Description

1 online resource (2, xi, 184 pages)

Abstract

Structure, stability, kinetics and mechanisms of oxidation of some physiologically important organosulfur compounds were studied and the results obtained show that oxidation occurs mainly at the reactive sulfur center of the molecules. These results not only display the usual S-oxygenation pathways that have been observed with most thiocarbamides, but also show dimerization and cyclization.

The oxidation of guanylthiourea, GTU, was studied in the presence of mildly acidic iodate and the strong oxidants bromate and bromine. The GTU reaction dynamics with iodate show clock reaction characteristics and oligooscillatory formation of iodine both in excess oxidant and reductant. The major oxidation product is a ring-cyclized product of guanylthiourea; 3,5-diamino-1,2,4-thiadiazole, in which the thioureido moiety is oxidized to the unstable sulfenic acid which instantly attacks the distal amino group eliminating water and forming the 5-membered thiadiazole group. In contrast to the iodate system, acidic bromate and molecular bromine, as stronger oxidizing agents, are able to oxidize GTU all the way to a complete desulfurization to yield guanylurea. The mechanism of the reaction involves initial formation of the ring-cyclized 3,5-diamino-1,2,4-thiadiazole which is later successively oxidized through the sulfoxide and sulfone, followed by the opening of the ring to yield sulfate and guanylurea.

The reaction of chlorite and thiourea is bistable and displays lateral instabilities that generate traveling waves of sulfate, acid and chlorine dioxide. The dynamics of the wave propagation are greatly influenced by the amount of heat generated at the wave front, which in turn is a function of reaction kinetics, enthalpy change, and extent of reaction. The chemical reaction studied here has shown complex propagative patterns, including convective rolls, double-diffusive convection, and spatiotemporal patterns. In this highly exothermic reaction the spatiotemporal patterns can be explained from the premises of a coupling between Marangoni and Rayleigh-Bernard convections.

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Persistent Identifier

https://archives.pdx.edu/ds/psu/39152

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