Photogeneration of meta and para quinone methides from quaternary ammonium salts
LE3 .A278 2009
Bachelor of Science
Quinone methides are reactive intermediates useful in many different organic reactions, both biological and synthetic. QMs are key intermediates being used in cancer treatments and prove to be useful in cross-linking DNA. In this project, we sought to develop an improved photochemical route to m and p-QMs by using quaternary ammonium salts. Quaternary ammonium salts were synthesized by reductive amination of hydroxybenzaldehydes followed by methylation with methyl iodide. Quantum yields for formation of QMs via photodehydration of o, m, p-hydroxybenzyl alcohols were 0.23, 0.12 and 0.007 respectively. The quantum yields from the Mannich bases and quaternary ammonium salts appeared to be much higher at 0.98 for each, indicating a much higher efficiency. Meta and para quinone methides formation from quaternary ammonium salts has not been studied previously. The QM intermediates formed were studied using Laser Flash Photolysis. LFP was used to gather information about rates and lifetimes of the QMs. 1H NMR spectroscopy was also used to characterize the photoproducts of all reactions. Quaternary ammonium salts have superior qualities than previously used QM precursors including high water solubility (making reactions in biological systems possible) and lower nucleophilicity (so the starting material is less likely to react with the intermediate).
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