Quinone-sensitized Steady-state Photolysis of Acetophenone Oximes Under Aerobic Conditions: Kinetics and Product Studies[dagger]

Photochemistry and Photobiology, Jan/Feb 2006 by Park, Adriana, Kosareff, Nicole M, Kim, Jason S, de Lijser, H J Peter

It is important to note that the LFP data only reflect the initial electron transfer step and do not take into account any follow-up reactions. A number of pathways can be proposed involving a variety of intermediates, both radicals and cations (Fig. 2). Depending on the structure of the intermediate(s), the effect of the substituents on the overall reaction is likely to be different from those on the first (electron transfer) step.

To address these issues we have undertaken a more extensive study involving the steady-state (SS) photolysis of meta- and parasubstituted acetophenone oximes. The photochemical experiments were complemented by electrochemical data as well as density functional theory (DFT) calculations on the neutral compounds and the radical cation species.

MATERIALS AND METHODS

Materials. All substituted acetophenone oximes were synthesized from their respective ketones, which were commercially available. Acetophenone oxime (98%), 3-methylacetophenone (98%), 3-(trifluoromethyl)acetophenone (98 %), 4-methylacetophenone (96%), 4-(trifluoromethyl)acetophenone (98 %), 3-chloroacetophenone (98 %), 4-chloroacetophenone (97%), 3-fluoroacetophenone (98%) and 4-fluoroacetophenone (98%) were obtained from Lancaster Synthesis, Inc. (Windham, NH). Acetophenone was obtained from Matheson, Coleman, and Bell (Norwood, OH). Benzophenone (98%), benzil (98%), anthracene (99%), p-chloranil (98 %), hydroxylamine hydrochloride (98%), 3-nitroacetophenone (99%), 4-nitroacetophenone (98%), 3-methoxyacetophenone (97%), 4-methoxyacetophenone (99%), 3-cyanoacetophenone (97%) and 4-cyanoacetophenone (99%), and 2,3,5,6-tetrabromohydroquinone (98%) were obtained from Sigma-Aldrich (Milwaukee, WI). p-Bromanil (98%) and 2,3,5,6-tetrachlorohydroquinone (98%) were obtained from TCI America (Portland, OR). p-Fluoranil (97%) was obtained from Acros (Fairlawn, NJ) and tetraethylammonium perchlorate was purchased from Eastman Kodak (Kingsport, TN). All solvents were HPLC grade and used as such. Anhydrous acetonitrile and water-^sup 18^O, normalized, 95 atom% ^sup 18^O were obtained from Sigma-Aldrich.

Synthesis of substituted acetophenone oximes. All oximes were prepared according to standard literature procedures (33). In general, hydroxylamine hydrochloride (15 mmol) was dissolved in 5 mL of water and 3 mL of 3 M sodium hydroxide solution, and the appropriate ketone (7.5 mmol) was added. To this mixture was added approximately 20-25 mL of 95% ethanol to create a clear solution, which was refluxed for 1 h. The solvent was removed via rotary evaporation, and the resulting product collected and dried by vacuum filtration. The crude product was dissolved in ether and extracted with water (~25 mL). The organic layer was dried over magnesium sulfate and the solvent was removed via rotary evaporation. The residue was further purified by recrystallization or column chromatography. The synthesized compounds were characterized by ^sup 1^H-NMR spectroscopy, infrared (IR) spectroscopy and melting point.