A Kinetic Study of 2-Ethyl-1-hexanol Oxidation by Dichromate Using Clay-Supported 1-Butyl 4-aza-1-azonia Bicyclo[2.2.2]octane Chloride as the Phase-Transfer Catalyst

摘要

Selective oxidation of primary alcohols to aldehydes is a long-standing problem of organic chemistry (Bueler, C. A.; Pearson, D. E. Survey of Organic Synthesis; Wiley-Interscience: New York, 1977; Vol. 2, p 480; House, H. O. Modern Synthetic Reactions, 2nd. ed.; W. A. Benjamin: Menlo Park, California, 1972; p 257; Epstein, W. W.; Sweet, F. W. Chem. Rev. 1967, 67, 247; Landini, D.; Montanari, F.; Rolla, F. Synthesis 1979, 134). The use of potassium dichromate as a synthetically useful oxidizing agent is reported for the oxidation of an industrially important lipophilic alcohol, employing modified clay as the phase-transfer catalyst. The phase-transfer catalysis results in nearly complete oxidation of the 2-ethylhexanol in 40 min at room temperature, with high selectivity to the 2-ethylhexanal, compared to 48 h in its absence. Kinetic studies show the reaction occurs via transfer of Cr_2O_7~(2-) into the organic phase. The emphasis will be on simplicity of the condition as a preparative organic method, selectivity with regard to over-oxidation, efficiency, and mildness of conditions.