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Mild conversion of beta-diketones and beta-ketoesters to carboxylic acids.

ABSTRACT: A mild protocol for the conversion of beta-ketoesters and beta-diketones to carboxylic acids with use of CAN in CH3CN is described. The method is compatible with a number of functional groups, and can generate carboxylic acids under neutral conditions at room temperature. The reaction is fast and general, providing an alternative method to the commonly used malonic ester acid preparation. Initial mechanistic studies show that initial oxidation of the enol form of the beta-dicarbonyl initiates the reaction. The presence of nitrate as an oxidant ligand or as an additive is critical for success of the reaction.

SUBMITTER: Zhang Y

PROVIDER: S-EPMC3668858 | biostudies-literature | 2006 Jun

REPOSITORIES: biostudies-literature

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Mild conversion of beta-diketones and beta-ketoesters to carboxylic acids.

Zhang Yang Y Jiao Jingliang J Flowers Robert A RA

The Journal of organic chemistry 20060601 12

A mild protocol for the conversion of beta-ketoesters and beta-diketones to carboxylic acids with use of CAN in CH3CN is described. The method is compatible with a number of functional groups, and can generate carboxylic acids under neutral conditions at room temperature. The reaction is fast and general, providing an alternative method to the commonly used malonic ester acid preparation. Initial mechanistic studies show that initial oxidation of the enol form of the beta-dicarbonyl initiates th ...[more]

PMID: 16749782

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Project description:Acetone is the expected ketone product of an acetic acid decarboxylative ketonization reaction with metal oxide catalysts used in the industrial production of ketones and for biofuel upgrade. Decarboxylative cross-ketonization of a mixture of acetic and isobutyric acids yields highly valued unsymmetrical methyl isopropyl ketone (MIPK) along with two less valuable symmetrical ketones, acetone and diisopropyl ketone (DIPK). We describe a side reaction of isobutyric acid with acetone yielding the cross-ketone MIPK with monoclinic zirconia and anatase titania catalysts in the absence of acetic acid. We call it a reketonization reaction because acetone is deconstructed and used for the construction of MIPK. Isotopic labeling of the isobutyric acid's carboxyl group shows that it is the exclusive supplier of the carbonyl group of MIPK, while acetone provides only methyl group for MIPK construction. More branched ketones, MIPK or DIPK, are less reactive in their reketonization with carboxylic acids. The proposed mechanism of reketonization supported by density functional theory (DFT) computations starts with acetone enolization and proceeds via its condensation with surface isobutyrate to a β-diketone similar to β-keto acid formation in the decarboxylative ketonization of acids. Decomposition of unsymmetrical β-diketones with water (or methanol) by the retrocondensation reaction under the same conditions over metal oxides yields two pairs of ketones and acids (or esters in the case of methanol) and proceeds much faster compared to their formation. The major direction yields thermodynamically more stable products-more substituted ketones. DFT calculations predict even a larger fraction of the thermodynamically preferred pair of products. The difference is explained by some degree of a kinetic control in the opposite direction. Reketonization has lower reaction rates compared to regular ketonization. Still, a high extent of reketonization occurs unnoticeably during the decarboxylative ketonization of acetic acid as the result of the acetone reaction with acetic acid. This degenerate reaction is the major cause of the inhibition by acetone of its own rate of formation from acetic acid at high conversions.

Dataset Information

Mild conversion of beta-diketones and beta-ketoesters to carboxylic acids.

Publications

Mild conversion of beta-diketones and beta-ketoesters to carboxylic acids.

Similar Datasets

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