Sarett oxidation

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Sarett oxidation
Named after Lewis Hastings Sarett
Reaction type Organic redox reaction
Identifiers
RSC ontology ID RXNO:0000547

The Sarett oxidation is an

carboxylic acid form, neither will it affect carbon-carbon double bonds.[1] Use of the original Sarett oxidation has become largely antiquated however, in favor of other modified oxidation techniques. The unadulterated reaction is still occasionally used in teaching settings and in small scale laboratory research.[2]

Schematic showing the oxidation of generic primary, and secondary alcohols into the respective aldehydes and ketones via the Sarett oxidation.

History

First appearance

Molecular structure of the Sarett/Collins reagent

The reaction is named after the American chemist

adrenal steroids
. The paper proposes the use of the pyridine chromium complex CrO3-2C5H5N to oxidize primary and secondary alcohols. The complex would later become known as the "Sarett Reagent".

Modifications and improvements

Although the Sarett reagent gives good yields of ketones, its conversion of primary alcohols is less efficient. Furthermore, the isolation of products from the reaction solution can be difficult.

pyrophoric properties make it difficult to prepare.[5] This issues lead to an improvement of the Collins oxidation protocol known as the Ratcliffe variant.[5][6]

Preparation of the Sarett reagent

Techniques

The brick-red color of unreacted chromium trioxide (chromic anhydride).

The Sarett reagent was originally prepared in 1953 by addition of chromium trioxide to pyridine.[3] The pyridine must be cooled because the reaction is dangerously exothermic. Slowly, the brick-red CrO3 transform into the bis(pyridine) adduct. Subsequent to the conversion to the Sarett reagent, it is immediately used.[3]

Safety

Improper handling of chromium trioxide can result in fire.

The specific methods of the reagent's preparation are critical, as improper technique can cause the explosion of the materials.[6] Some technical improvements to the original methodology have reduced the risks associated with preparation. One such recent improvement reduced the likelihood of explosion by using chromic anhydride granules that would immediately sink below the surface of the cooled pyridine upon addition.[2] It should also be mentioned that chromium trioxide is a corrosive carcinogen and therefore must be handled with extreme care.[7]

Collins technique

The original Collins oxidation calls for the Sarett reagent to be removed from the excess pyridine and dissolved in the less basic methylene chloride.[4][6] While the new solvent improves the overall yield of the reaction, it also requires the dangerous transfer of the pyrophoric reagent. The 1970 Ratcliffe variation reduced the risk of explosion by calling for the Sarett reagent to be made in situ. This was achieved by creating the Sarett reagent according to the original protocol using a stirred mixture of pyridine and methylene chloride.[5]

Specific applications

The Sarett oxidation efficiently oxidizes primary alcohols to aldehydes without further oxidizing them to carboxylic acids.

thioether groups.[3] These groups cannot effectively interact with the chromium of the Sarett reagent, as compared to the chromium in oxidizing complexes used prior to 1953.[3]

See also

References

  1. ^ Margareta Avram (1983). "Chimie organica" p. 472. "Editura Academiei Republicii Socialiste România"
  2. ^
    S2CID 97957064
    .
  3. ^
    doi:10.1021/ja01098a049
    .
  4. ^
    doi:10.1016/s0040-4039(00)89494-0
    .
  5. ^
    doi:10.1021/jo00836a108
    .
  6. ^
    ISBN 978-0-387-23607-0
    .
  7. ^ "Chromium Trioxide (MSDS)". J. T. Baker. Retrieved 2007-09-13.
  8. ^ "Jones Oxidation". organic-chemistry.org.

External links

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