Ketonic decarboxylation

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Ketonic decarboxylation (also known as ketonization) is a type of organic reaction and a decarboxylation converting two equivalents of a carboxylic acid to a symmetric ketone by the application of heat with expulsion of one equivalent of water and one equivalent of carbon dioxide.[1] Bases promote this reaction. The reaction mechanism likely involves formation of an intermediate carbanion with decarboxylation from one acid group followed by nucleophilic attack on the other acid group as a concerted reaction. This reaction is different from oxidative decarboxylation with proceeds through a radical mechanism and is characterised by a different product distribution in isotopic labeling experiments with two different carboxylic acids.

Examples[edit]

The dry distillation of calcium acetate to acetone was reported by Charles Friedel in 1858 [2] and until World War I ketonization was the premier commercial method for its production.[3]

The synthesis of 3-pentanone from propanoic acid over a manganese(II) oxide catalyst in a tube furnace.[4]

With two different carboxylic acids the reaction behaves poorly because of poor selectivity except when one of the acids (small, volatile) is used in large excess. An example of intramolecular ketonization is the conversion of adipic acid to cyclopentanone with barium hydroxide.[5] Of commercial importance is the production of 3-pentanone from propionic acid with catalysts cerium(IV) oxide and manganese dioxide on alumina.

References[edit]

  1. ^ Renz, M. (2005), Ketonization of Carboxylic Acids by Decarboxylation: Mechanism and Scope. Eur. J. Org. Chem., 2005: 979–988. doi:10.1002/ejoc.200400546
  2. ^ Friedel, C. (1858), Ueber s. g. gemischte Acetone. Justus Liebigs Ann. Chem., 108: 122–125. doi:10.1002/jlac.18581080124
  3. ^ IMPROVEMENT IN THE MANUFACTURE OF ACETONE.1 E. R. Squibb Journal of the American Chemical Society 1895 17 (3), 187-201 doi:10.1021/ja02158a004
  4. ^ Furniss, Brian; Hannaford, Antony; Smith, Peter; and Tatchell, Austin (1996). Vogel's Textbook of Practical Organic Chemistry 5th Ed.. London: Longman Science & Technical. p. 613. ISBN 9780582462366. 
  5. ^ J. F. Thorpe and G. A. R. Kon (1925), "Cyclopentanone", Org. Synth. 5: 37 ; Coll. Vol. 1: 192 .