Photo-Oxidation of
Aldehydes with
Molecular Oxygen in the Presence ofCatalytic
Bromine or
Hydrobromic Acidby Shin-ichi HIRASHIMA and Akichika ITOHThe notion of green chemistry is becoming well established, and the development of environmentally benign processes is the goal of various research projects.1) The method using molecular oxygen is one way consistent with this notion due to its high atomic effect or E-factor as an oxidant. With this background in mind, we have been engaged in aerobic photo-oxidation of alcohols and a methyl group at the aromatic nucleus with several bromo sources.2—8) In the course of our further study for expanding application of this reaction, aldehydes were found to be oxidized to the corresponding carboxylic acids in the presence of catalytic
lithium bromide.9) Although lithium
bromide is undoubtedly an inexpensive and safe reagent, it is not necessarily easy to handle due to its hygroscopic property and the promoting effect of lithium bromide is presumed to be lower than that of other bromo sources, bromine or hydrobromic acid, by our previous experiments.3—7) Herein, we report in detail our study on the generality and limitation of this aerobic photo-oxidation of aldehydes to the carboxylic acids10—22) in the presence of a catalytic bromine or hydrobromic acid, which are inexpensive, safe and easily separable from the reaction mixture by extraction.Chem. Pharm. Bull. 55(1) 156—158 (2007) Vol. 55, No. 1
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