| Abstract
| - When a solution of a carbonyl compound in alcohol (primary or secondary) is heated to ca. 300 °C,a disproportionation reaction, in which a carbonyl compound is reduced to the corresponding alcoholand the alcohol is oxidized to the corresponding ketone, takes place. This uncatalyzed variation ofthe Meerwein−Ponndorf−Oppenauer−Verley reaction gives, in certain cases, e.g., reduction ofacetophenone or benzaldehyde by i-PrOH, almost quantitative yields. Yields are higher withsecondary alcohols such as i-PrOH than with a primary alcohol such as EtOH. The reactions werealso performed in a flow system by passing at a slow rate the same solutions through a glass or ametal coil heated to elevated temperatures. Ab initio calculations performed at the B3LYP/6-31G*level show that thermodynamically i-PrOH is a more potent reducing agent than EtOH by ca. 4kcal/mol. The computations also show that in cases of aromatic carbonyl compounds, part of thederiving force is obtained from the entropy change of the reaction. The major contributor to thehigh yield, however, is the excess alcohol used, which shifts the equilibrium to the right. Calculatedentropy of activation as well as isotopic H/D labeling suggest a cyclic transition state.
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