Jones oxidation

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The Jones oxidation is an organic reaction for the oxidation of primary and secondary alcohols to carboxylic acids and ketones, respectively. It is named after its discoverer, Sir Ewart Jones.[1]

The Jones oxidation

Jones reagent is a solution of chromium trioxide in dilute sulfuric acid and acetone. A mixture of potassium dichromate and dilute sulfuric acid can also be used. The solvent acetone markedly affects the properties of the chromic acid. The oxidation is very rapid, quite exothermic, and the yields are typically high. The reagent rarely oxidizes unsaturated bonds.

Stoichiometry[edit]

Jones reagent will convert primary and secondary alcohols to aldehydes and ketones, respectively. Depending on the reaction conditions, the aldehydes may then be converted to carboxylic acids. For oxidations to the aldehydes and ketones, two equivalents of chromic acid oxidize three equivalents of the alcohol:

2 HCrO4 + 3 RR'C(OH)H + 8 H+ + 4 H2O → 2 [Cr(H2O)6]3+ + 3 RR'CO

For oxidation of primary alcohols to carboxylic acids, one equivalent of Jones reagent is required for each substrate. The aldehyde is an intermediate.

4 HCrO4 + 3 RCH2OH + 16 H+ + 11 H2O → 4 [Cr(H2O)6]3+ + 3 RCOOH

The inorganic products are green, characteristic of chromium(III) aquo complexes.[2]

Mechanism[edit]

Like many other oxidations of alcohols by metal oxides, the reaction proceeds via the formation of a mixed ester:[3][4] These esters have the formula CrO3(OCH2R)

CrO3(OH) + RCH2OH → CrO3(OCH2R) + H2O

Like conventional esters, the formation of this chromate ester is accelerated by the acid. These esters can be isolated when the alcohol lacks α-C-H bonds. For example, using tert-butyl alcohol, one can isolate ((CH3)3CO)2CrO2 (which is a good oxidant).[5] The chromate esters degrade, releasing the carbonyl product and an ill-defined Cr(IV) product:

CrO3(OCH2R) → "CrO2OH" + O=CHR

The partially deuterated alcohols HOCD2R oxidize about six times slower than the undeuterated derivatives. This large kinetic isotope effect shows that the C–H (or C-D) bond breaks in the rate-determining step. The reaction stoichiometry implicates the Cr(IV) species "CrO2OH", which comproportionates with the chromic acid to give a Cr(V) oxide, which also functions as an oxidant for the alcohol.[6]

The oxidation of the aldehydes is proposed to proceed via the formation of hemiacetal-like intermediates, which arise from the addition of the O3CrO-H- bond across the C=O bond.

Illustrative reactions and applications[edit]

Although useful reagent for some applications, due to the carcinogenic nature of chromium(VI), the Jones oxidation has slowly been replaced by other oxidation methods. It remains useful in organic synthesis.[2][7] A variety of spectroscopic techniques, including IR can be used to monitor the progress of a Jones Oxidation reaction and confirm the presence of the oxidized product. At one time the Jones oxidation was used in primitive breathalyzers. [8] Aminoindans, which are of pharmalogical interest, are prepared by the oxidation of the alcohol to ketone which is converted into an amino group. The alcohol is oxidized to the ketone with the Jones reagent. The reagent was once used to prepare salicylic acid, a precursor to aspirin.[9] Methcathinone is a psychoactive stimulant that is sometimes used as an addictive recreational drug. It can be oxidized from certain alcohols using the Jones reagent.[10]

Related reagents[edit]

Several chromium oxides are used for related oxidations.[3] These include Collins reagent and pyridinium chlorochromate The Sarett oxidation is a similar process.

References[edit]

  1. ^ Bowden, K.; Heilbron, I. M.; Jones, E. R. H (1946). "13. Researches on acetylenic compounds. Part I. The preparation of acetylenic ketones by oxidation of acetylenic carbinols and glycols". J. Chem. Soc.: 39. doi:10.1039/jr9460000039. 
  2. ^ a b E. J. Eisenbraun (1973), "Cyclooctanone", Org. Synth. ; Coll. Vol. 5: 310 
  3. ^ a b Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, ISBN 0-471-72091-7 
  4. ^ Ley, S. V.; Madin, A. (1991). B. M. Trost and I. Fleming, ed. Comprehensive organic synthesis 7. Oxford: Pergamon Press. pp. 253–256. 
  5. ^ Fillmore Freeman, "Di-tert-butyl Chromate" Encyclopedia of Reagents for Organic Synthesis, 2001, John Wiley & Sons, Ltd. doi:10.1002/047084289X.rd059m
  6. ^ Oxidation in Organic Chemistry. Edited by K. B. Wiberg, Academic Press, NY, 1965.
  7. ^ J. Meinwald, J. Crandall, and W. E. Hymans (1973), "Nortricyclanone", Org. Synth. ; Coll. Vol. 5: 866 
  8. ^ Freudenrich, Craig. "How Breathalyzers Work". How Stuff Works. Retrieved April 2011. 
  9. ^ Alcohol Unknown (NMR)/Synthesis of Aspirin
  10. ^ Solomons, E.; Sam, J. (1973). "2-Aminoindans of pharmacological interest". Journal of Medicinal Chemistry 16 (12): 1330–1333. doi:10.1021/jm00270a004. PMID 4765859. 

Historical references[edit]

  • Heilbron, I.M.; Jones, E.R.H.; Sondheimer, F (1949). "129. Researches on acetylenic compounds. Part XV. The oxidation of primary acetylenic carbinols and glycols". J. Chem. Soc.: 604. doi:10.1039/jr9490000604. 
  • Bladon, P; Fabian, Joyce M.; Henbest, H. B.; Koch, H. P.; Wood, Geoffrey W. (1951). "532. Studies in the sterol group. Part LII. Infra-red absorption of nuclear tri- and tetra-substituted ethylenic centres". J. Chem. Soc.: 2402. doi:10.1039/jr9510002402. 
  • Jones, E. R. H (1953). "92. The chemistry of the triterpenes. Part XIII. The further characterisation of polyporenic acid A". J. Chem. Soc.: 457. doi:10.1039/jr9530000457. 
  • Jones, E. R. H (1953). "520. The chemistry of the triterpenes and related compounds. Part XVIII. Elucidation of the structure of polyporenic acid C". J. Chem. Soc.: 2548. doi:10.1039/jr9530002548. 
  • Jones, E. R. H (1953). "599. The chemistry of the triterpenes and related compounds. Part XIX. Further evidence concerning the structure of polyporenic acid A". J. Chem. Soc.: 3019. doi:10.1039/jr9530003019. 
  • C. Djerassi, R. Engle and A. Bowers (1956). "Notes – The Direct Conversion of Steroidal Δ5-3β-Alcohols to Δ5- and Δ4-3-Ketones". J. Org. Chem. 21 (12): 1547–1549. doi:10.1021/jo01118a627.