Corey-Schmidt oxidation

What is Corey-Schmidt oxidation?

The Corey and Schmidt reaction, which was first documented in 1979, is also known as the PDC oxidation because it employs pyridinium dichromate (PDC) for the oxidation of inorganic compounds.

Corey-Schmidt oxidation
Corey-Schmidt oxidation

R = alkyl, aryl
R’ = H, alkyl, aryl

Corey-Schmidt oxidation
Corey-Schmidt oxidation

R = alkyl, aryl

PDC is a stable orange solid that can be produced by dissolving CrO3 in a small volume of water, then precipitating it with pyridine. PDC has lower acidity than PCC, but higher acidity than the Collins reagent. Depending on the substrate and solvent, primary alcohols can be oxidized to aldehydes, carboxylic acids, or esters. When suspended in dichloromethane, PDC oxidizes primary alcohols to aldehydes, whereas in DMF, it converts them into carboxylic acids or methyl esters if methanol is present. PDC can also oxidize the aldehyde group into a carboxylic group in DMF solvent. However, the oxidation of alcohols to other esters is not successful. Secondary alcohols can also be oxidized to ketones using PDC. Moreover, in the presence of t-butyl hydroperoxide, PDC can oxidize active methylene groups into carbonyl groups. PDC alone, however, cannot affect the benzyl ethers of alcohols. Compared to other chromium-based oxidations (for example: Fieser, Jones, CrO3/AcOH, and pyridinium chlorochromate), the Corey-Schmidt oxidation has some advantages in the oxidation of diols into diketones, yielding higher product yields and fewer byproducts. Nevertheless, PDC oxidation using PDC is ineffective when a methylamino group is present in the substrate alcohol.

References

E.J. Corey, Greg Schmidt,
Useful procedures for the oxidation of alcohols involving pyridinium dichromate in aprotic media,
Tetrahedron Letters 20 (5) 399-402 (1979)
DOI: 10.1016/S0040-4039(01)93515-4

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