RADICAL CATALYZED RACEMIZATION OF OPTICALLY ACTIVE 2,2'-DICARBOMETHOXY-9,9'-BIANTHRYL.
Item
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Title
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RADICAL CATALYZED RACEMIZATION OF OPTICALLY ACTIVE 2,2'-DICARBOMETHOXY-9,9'-BIANTHRYL.
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Identifier
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AAI8023693
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identifier
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8023693
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Creator
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CHEN, CHING HONG.
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Contributor
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Leonard H. Schwartz
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Date
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1980
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Organic
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Abstract
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The racemization of optically active 2,2'-dicarbomethoxy-9,9'-bianthryl (Ia), in several media, has been studied. It was discovered that the racemization of Ia in the presence of oxygen or diphenyl disulfide or dibenzyl mercury or tert- butyl peroxide occurs more easily than in the absence of these substances. In the presence of oxygen, the rotation of a solution of Ia lost 87% of its original value on heating at 148.8 (+OR-) 0.1(DEGREES)C for two hours. The starting material was recovered in 41% yield from the heated material. This chemically unchanged Ia was 62% racemized. In the presence of diphenyl disulfide, racemization occurred to the extent of 45% after 96 hours heating at 197.0 (+OR-) 0.1(DEGREES)C. The chemically unchanged starting material was recovered in 78% yield. It was 45% racemized. In the presence of dibenzyl mercury, the degree of racemization was found to be 70% after heating at 187.0 (+OR-) 0.1(DEGREES)C for two hours. Eighty percent of the starting material was recovered. It was 72% racemized. In the presence of tert- butyl peroxide, the degree of racemization was found to be 82.5% after heating at 124.7 (+OR-) 0.1(DEGREES)C for 2.5 hours. Twenty five percent of the starting material was recovered. It was 41% racemized.;In all the above systems, it was demonstrated that radicals initiated by these substances were the species which catalyzed the racemization of Ia. These include radicals derived from triglyme by autoxidation, radicals derived from hydrogen abstraction of triglyme by phenylthiyl radicals, benzyl radicals derived from the thermolysis of dibenzyl mercury and radicals derived from hydrogen abstraction of dimethyl suberate by oxygen-containing radicals (derived from tert-butyl peroxide) or by benzyl radicals.;It is postulated that the addition of a radical to Ia results in the formation of a 1,4-cyclohexadienyl radical complex ((sigma) - complex). The boat conformation of this radical complex permits the two benzo-benzo interactions, during the rotation of the central bond (C(,9)-C(,9),), to occur consecutively instead of simultaneously. The rotational barrier is thus reduced. Therefore, racemization of the radical complex of Ia can occur more rapidly than in the case of Ia.;The recovery of chemically unchanged racemized Ia demonstrates that the addition of a radical to the aromatic ring of Ia is reversible. It is suggested that the observation of racemization of optically active biaryls would be a useful tool in a study of the reversibility of the first step of homolytic aromatic substitution reactions.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Chemistry
