Abstract
Alcohols were found to be oxidized to the corresponding carboxylic acids in the presence of catalytic lithium bromide under photoirradiation.
Key words
photooxidation - alcohols - lithium bromide
- aerobic - carboxylic acid
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4a For direct oxidations of alcohols to carboxylic acid without photoirradiation, see ref. 1. See also:
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5 We believe an effective wavelength of light is 365 nm.
6 When using primary alcohol as substrate, a typical procedure follows: a solution (5 mL) of the substrate (50 mg) and LiBr (0.3 equiv) in dry EtOAc was stirred and irradiated at r.t. with a 400 W high-pressure mercury lamp externally for the indicated time. The reaction mixture was concentrated under reduced pressure, and 1% NaOH aq solution was added. The aqueous solution was washed with Et2O, and then acidified with 2 N HCl aq solution, which was extracted with Et2O. The organic layer was washed with brine and dried over Na2SO4, and concentrated under reduced pressure. The product was pure without further purification.
When using secondary alcohol as substrate, a typical procedure follows: a solution (5 mL) of the substrate (50 mg) and LiBr (0.3 equiv) in dry EtOAc was stirred and irradiated at r.t. with a 400 W high-pressure mercury lamp externally for the indicated time. The reaction mixture was concentrated under reduced pressure, and 1% NaOH aq solution was added. The aqueous solution was washed with Et2O and the organic layer was concentrated, and the residue was purified by preparative TLC. The aqueous layer was then acidified with 2 N HCl aq solution and extracted with Et2O the same as in the former cases.
7 Catalytic bromine oxidized 1 to 2 in 59% yield under similar conditions.
