Chemiluminescent autoxidation of linolenic acid films on silica gel

Films of linolenic acid supported on chromatographic type silica gel undergo autoxidation at a rate which is slow compared to that in homogeneous phase at low surface coverage but comparable to it at coverages approximating a close‐packed monolayer. The new observation reported here is that these surface phase oxidations are chemiluminescent. The quantum yield is ca. 10 −12 quanta per molecule of fatty acid reacted for a close‐packed monolayer and remains approximately constant with decreasing coverage. The emission intensity is temperature dependent, with an apparent activation energy of 10 kcal mol −1 , and shows an induction period for close‐packed monolayers. The emission spectrum contains a component consistent with excited state ketone emission and a low energy component, ca. 600+ nm, which could be due to singlet oxygen emission. The existence of the emission means that surface autoxidation reactions can be followed in place; the nature of the emission may provide insight into the autoxidation mechanism beyond that which may be inferred from conventional rate measurements.