Doctor of Philosophy
Lawrence J. Winters
The unique combination of properties of bipyridinium salts and their use in biological systems, chemical reactions, and as herbicides in agriculture have made them a discovery of major international importance. The controversy about the position of attack of the cyanide ion on the pyridine ring and the discovery of the formation of unsubstituted bipyridinium salts from the reaction of pyridinium salt with cyanide ion opened a new area of research. The current work involved a study of reactions of substituted pyridinium salts with cyanide ion. The substituted pyridinium salts were prepared by the literature methods. The 2- and 3- cyanopyridinium salts reacted with cyanide ion to form 4-cyano-1, 4-dihydropyridines. The 3, 4-dicyano-1, 4-dihydropyridines were very stable; therefore, they were isolated and characterized. An unusual product, 1-methyl-2-oxo-1, 2-dihydro-4-pyridine carbonitrile, was isolated from the reaction of 1-methyl-2-cyanopyridinium iodide with cyanide ion.
The reaction of 1-benzyl-2-(acylamino) pyridinium bromide with cyanide ion did not form a 1, 4-dihydropyridine; rather, hydrogen bromide was lost when the reaction mixture was heated to a boil and 1-benzylpyridinium-2-acylimide was formed. The reaction of the 1-benzyl-2-acetylpyridinium salt, the 1-benzyl-2-bromopyridinium salt, and the 1-benzyl-2-ethylpyridinium salt with cyanide ion formed complicated products that were not characterized.
The reactions of 1-benzyl-2-methylpyridinium bromide, 1-benzyl-2-(hydroxymethyl) pyridinium bromide and 1-benzyl-2, 6-dimethylpyridinium bromide with cyanide ion in water, acetone, acetone-water or 95% ethanol solutions formed dark blue or green solutions. Electron spin resonance spectroscopy showed the presence of a radical in the dark-blue or green solutions. A dark solid formed from the solutions. Oxidation of the solid with an acetone and ethanolic iodine solution or acidic ethanol solution resulted in the formation of the corresponding new, 1, 1'-dibenzyl-2, 2'-bis(hydroxymethyl)-4-4'-bipyridinium dibromide 75, and the known 1, 1'-dibenzyl-2, 2'-dimethyl-4, 4'-bipyridinium dibromide, and 1, 1'-dibenzyl-2, 2', 6, 6'-tetramethyl-4, 4'-bipyridinium dibromide dimers.
The new dimer 75 was reduced in aqueous solution at potential (E°) of about -0.34V vs NHE. It was also debenzylated with triphenylphosphine in refluxing DMF to give 2, 2'-bis(hydroxymethyl)-4, 4'-bipyridine 89. 1, 1'-Dibenzyl-2, 2'-dimethyl-4, 4'-bipyridinium dibromide was also debenzylated to give 2, 2'-dimethyl-4, 4' bipyridine, which was acidified with hydrogen chloride gas, and the salt 2', 2'-dimethyl-4, 4'-bipyridyl dihydrochloride was formed. These were the first report on debenzylation of bipyridinium dimers. The reaction of 89 with cobalt thiocyanate formed a new 2, 2'-bis(hydroxymethyl)-4, 4'-bipyridine cobalt thiocyanate octahedral complex. The reaction of 2-(hydroxymethyl)pyridine and 2-(2-hydroxyethyl) pyridine with cobalt thiocyanate gave the corresponding octahedral complexes.
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