Date of Award

1-1-1981

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Abstract

A small-scale 12-ml hydrogenation apparatus was designed and built. The objectives of the design were: (a) to minimize heat-up and cool-down times, (b) to minimize the time per reaction run, (c) to be able to utilize small samples, e.g., 0.5 g, for expensive compounds, (d) to be able to monitor both pressure and temperature during the course of the reaction and (e) to be able to achieve 500(DEGREES)C and 3000 psi. The short heat-up and cool-down times of the reactor enabled reliable kinetic studies to be done.High temperature desulfurization and reduction reactions of diphenyl sulfide and other aryl sulfur compounds were studied in the small-scale hydrogenation apparatus under conditions approximating those used in coal liquefaction. The primary objectives were to understand the mechanisms of sulfur removal with the reducing systems of CO-H(,2)O, formic acid, H(,2) and tetralin. Hydrogen sulfide (H(,2)S) was found to enhance the cleavage of diphenyl sulfide at the expense of increased sulfur content in the products.Hydrogen and formic acid were found to be the most effective desulfurization and reducing systems for diphenyl sulfide. The mixture of CO and H(,2)O, which forms reducing gases in the presence of H(,2)S, was found to be a favorable reduction system for diphenyl sulfide. By comparison, tetralin does little to promote conversion of diphenyl sulfide and furthermore it is found to inhibit conversion when hydrogen is used. Carbon monoxide was also shown to be effective in removing aryl sulfur from thiophenol radicals (PhS(.)). This result is analogous to that found by Berenblyum and co-workers, whereas, CO removes sulfur from aliphatic sulfur radicals (RS(.)).The mechanisms of carboxylation to benzoic acid and methylation to toluene in the diphenyl sulfide -CO-H(,2)O and/or formic acid reactions were determined by kinetic data and comparing CO and CO(,2) as possible sources for the extra carbon. It was concluded that thiophenol radicals (PhS(.)) and CO are the precursors to carboxylation. Furthermore, only aryl sulfur compounds when treated with CO-H(,2)O and/or formic acid afford carboxylation and methylation products. Carboxylation and methylation occurs at the ipso position on the aromatic ring, that is, the site where sulfur was bound to the ring. Water is needed for optimization of carboxylation product, however, methylation is independent of the presence or absence of water.When thioanisole is pyrolyzed at 450(DEGREES)C the major product is toluene. By utilizing the compounds ethyl phenyl sulfide and methyl-p-tolyl sulfide, for crossover experiments, the mechanism of toluene formation from thioanisole was determined to occur predominately by an intramolecular rearrangement. This result supports the analogous finding of Collins and co-workers for rearrangement of aryl alkyl ethers.

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