Chemistry and Chemical Biology ETDs

Publication Date

1969

Abstract

A study has been initiated in order to understand more completely the manner in which a model organic scintil­lator decomposes in ultraviolet light. The compound, 2,5-diphenyloxazole (PPO), was dissolved in toluene in quartz vials and irradiated with ultraviolet light for various intervals of time. Both. vacuum-dried and untreated samples of PPO \·1ere subjected to UV excitation in sodium-dried and water-saturated solutions of toluene. The effect of passing oxygen and nitrogen through the solutions was also studied with the confirmation that dissolved oxygen and water accelerated the decomposition leading to the formation above the meniscus of the vial of a white crystalline solid with a previously reported empirical formula of C22H17O5N, m.p. 142-144^0, dec.

The decomposition process leading to the formation of the crystalline product, identified earlier as a tertiary amide, was studied through the use of thin layer chromatography (TLC). Experiments were designed to ascertain the combina­tions of solvents and adsorbants most suitable for the separation of the products of the irradiation.

The TLC studies with the irradiated PPO showed that the first decomposition product to appear exhibited an Rf equal to that of N-formylbenzamide, m. p. 112-113° and N-formyldibcnzamide hydrate, m. p. 78-80°. The compoundwas indicated to be H-formyldibenzamide hydrate as a result of melting point and mixed melting point determinations taken on the sample collected from a TLC preparative plate. This information led to the justification for a mechanism involving a 1, 4--peroxidation of the oxazole ring which would rearrange to form N-formyldibenzamide. A mechanism involving an initial 1,2-peroxidation forming N-phenylglyoxylbenzamide is discarded because no initial formation of the latter compound was observed.

The second compound to be observed in the irradiation had an Rf and shape similar to dibenzamide. It was felt that dibenzamide (C14H1102N) and N-formyldibenzamide(C15H1103N) might combine to form a molecule of the photooxidation product (c22H17o5N) and a molecule of benzonitrile (C7H5N) since benzonitrile has been observed in PPO irradiations of longer duration. The photooxidation product, however, was not obtained by irradiation of the proposed reactants.

The TLC data, however, did not disprove the suggested structure of the photooxidation product, N-(phenylglyoxyl) dibenzamide hydrate.

Thin layer chromatography tables were compiled for systems found to be most useful throughout the investigation. These data were provided as an aid for future studies of a similar nature and for the characterization of complex amides and related compounds.

Tables were prepared listing the methods and para­meters found to be best suited for photography of the TLC plates. Conditions were given for ultraviolet photography of plates containing short wavelength UV indicators.

Document Type

Thesis

Degree Name

Chemistry

Level of Degree

Masters

Department Name

Department of Chemistry and Chemical Biology

First Committee Member (Chair)

Guido Daub

Second Committee Member

Raymond N. Castle

Third Committee Member

Roy Dudley Caton Jr.

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