| Collins oxidation | |
|---|---|
| Named after | Joseph C. Collins |
| Reaction type | Organic redox reaction |
| Identifiers | |
| RSC ontology ID | RXNO:0000550 |
TheCollins oxidation is anorganic reaction for theoxidation of primary alcohols toaldehydes. It is distinguished from other chromium oxide-based oxidations by the use ofCollins reagent, a complex ofchromium(VI) oxide withpyridine indichloromethane.[1][2]
![Mechanism of the Collins oxidation[3]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aAlcohol_oxidation_with_Collins_reagent.svg)
The mechanism of the Collins oxidation is a relatively simple oxidation process.
The collins oxidation first came about in 1968 when J.C. Collins used pre-formed CrO3•2Pyr dissolved indichloromethane to oxidize alcohols.[5] Although difficult, it was beneficial at the time because it provided an alternative to theSarett oxidation, that usedpyridine as asolvent.[5] The Collins oxidation allowed for a less basic reagent, which in turn provided a useful option for oxidation of primary alcohols to aldehydes.[5]
A safer variant of the Collins oxidation was discovered in 1970 by Ratcliffe and Rodehorst. The variant featured anin situ preparation of the Collins reagent by adding one equivalent of CrO3 over two equivalents ofpyridine indichloromethane.[5]
The Collins oxidation is also very useful because it is cheap in comparison to its oxidizing counterparts,PCC andPDC.[5] However, it is more difficult experimentally because of its requiredanhydrous conditions. The Collins oxidation is a good option when using uncomplicatedsubstrates because it produces good yields ofaldehyde andketone products.[5] However, as the complexity of the substrates increases, the usefulness of the Collins oxidation decreases because it lacks the selectivity that other reagents have.[5]
One of the main uses of the Collins oxidation is the transformation ofalkenes toenones by addingcarbonyl groups toallylic positions. While this process is very slow, it allows for alcohols to beoxidized toaldehydes orketones without alkene interference.[3]
The Collins oxidation can also be used to form cyclic chromateesters from 1,2-diols in order to them intramolecularly oxidizealkenes. This process can then result in the formation of highlystereoselectivetetrahydrofuran.[3]
Several chromium oxides are used for related oxidations.[6] These includeJones oxidation andSarett oxidation.