Chemistry and Chemical Biology ETDs

Publication Date

9-9-1970

Abstract

Mackay had found that prolonged ultraviolet irradiation of solutions of 2,5-diphenyloxazole (PPO) (1) in toluene resulted in the formation of an insoluble crystalline product 2 which accumulated above the meniscus; the formation of 2 was dependent upon the presence of dissolved oxygen and water in the solutions. The Compound 2 was not a simple degradation product of PPO (1); elemental analysis was compatible with the empirical formula C22H17O5N and the thermal decomposition of 2 gave equal molar amounts of carbon monoxide, benzoic acid, and dibenzamide. The study described in this dissertation was initiated to establish the structure of 2 and to determine the mechanism by which it formed. The formation of 2 was dependent upon the wavelength of light employed for irradiation. Only radiation in the range absorbed by 1 (2700-3400 Å) was effective. In order to decrease the time necessary to obtain substantial quantities of 2, sensitizers were investigated. In agreement with recent studies by Foote and others, only sensitizers producing singlet oxygen were effective. The methylene blue sensitized photooxidation of 1 in methanol at 23° resulted in the production of benzoic acid, N-formylbenzamide (3), methyl benzoate, and benzoitrile along with a small quantity of a new compound. This material melted with violent decompostion and was capable of liberating iodine from sodium iodide. It was initially thought to be the ozonide 4, however, elemental analyses, NMR spectrum, and analyses of the products from autodecomposition have shown it to be the methoxyperoxide 5 resulting from the addition of methanol to 4. Reducing the temperature of the photooxidation to 0° allowed the isolation of 5 in 80 per cent yield. At present, the data are insufficient to establish the exact structure of 5 or the mechanism for its decomposition. The methylene blue sensitized photooxidation of 1 in chloroform at 0° resulted in the formation of a solid in the reaction solution during irradiation. Upon isolation, this material was found to be identical to the C22H17O5N (2) compound from the unsensitzed toluene irradiations of 1. The other products of the photooxidation were benzoic acid, N­formylbenzamide (3), and benzonitrile. The molar amount 3 was equal to the sum of the molar amounts of 2 and benzoic acid. The yields of these products were found to be dependent upon the amount of water present in the reaction mixture. The photooxidation of 1 in chloroform saturated with water gave only benzoic acid and 3. Partial drying of the system gave 40-70 per cent yields of 2 whereas the exclusion of moisture from the reaction allowed the photooxidation on of 1 with the formation of none of these products until water was added. The addition of an amount of water equal to one-half the molar quantity of 1 that had been oxidized produced an 82 per cent yield of 2. The reactive intermediate was isolated from an anhydrous photooxidation and identified by NMR, lR, and mass spectral studies as N-formyldibenzamide (6). The IR and NMR spectra of 2 had indicated that it was N-(benzoyloxyhydroxymethyl)-dibenzamide. Initially, this structure was thought to have formed via the acylation of N-formyldibenzamide hydrate (7) by 6; however, the hydrate 7 was found to be N-(benzoyloxyhydroxymethyl)benzamide (8) resulting from the reaction of benzoic acid and 3. Consequently, 2 was proposed to form from the reaction of 6 with benzoic acid arising from the decomposition of 8. Indeed, the addition of an amount of benzoic acid, equal to the molar amount of 1 which had been photooxidized, to an anhydrous reaction solution produced a 90 per cent yield of 2.

Project Sponsors

The Division of Biology and Medicine of the U.S. Atomic Energy Commission Contract No. AT(29-2)915

Document Type

Dissertation

Degree Name

Chemistry

Level of Degree

Doctoral

Department Name

Department of Chemistry and Chemical Biology

First Committee Member (Chair)

Guido Herman Daub

Second Committee Member

F. Newton Hayes

Third Committee Member

Milton Kahn

Fourth Committee Member

Nicholas Ernest Vanderborgh

Fifth Committee Member

Eleftherios Paul Papadopoulos

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