PCC; Corey-Suggs reagent
3D model (JSmol)
|Molar mass||215.56 g/mol|
|Melting point||205 °C (401 °F; 478 K)|
|Solubility in other solvents||soluble in acetone, acetonitrile, THF|
|Main hazards||Toxic, oxidizer, carcinogenic, strong environmental pollutant|
|Safety data sheet||external SDS|
|GHS Signal word||Danger|
|H272, H317, H350, H410|
|P201, P280, P273, P221, P308+313, P302+352|
|NFPA 704 (fire diamond)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Pyridinium chlorochromate (PCC) is a yellow-orange salt with the formula [C5H5NH]+[CrO3Cl]−. It is a reagent in organic synthesis used primarily for oxidation of alcohols to form carbonyls. A variety of related compounds are known with similar reactivity. PCC offers the advantage of the selective oxidation of alcohols to aldehydes or ketones, whereas many other reagents are less selective.
Structure and preparation
PCC consists of a pyridinium cation, [C5H5NH]+, and a tetrahedral chlorochromate anion, [CrO3Cl]−. Related salts are also known, such as 1-butylpyridinium chlorochromate, [C5H5N(C4H9)][CrO3Cl] and potassium chlorochromate.
- C5H5N + HCl + CrO3 → [C5H5NH][CrO3Cl]
In one alternative method, formation of chromyl chloride (CrO2Cl2) fume during the making of the aforementioned solution was minimized by simply changing the order of addition: a cold solution of pyridine in concentrated hydrochloric acid was added to solid chromium trioxide under stirring.
Oxidation of alcohols
PCC is used as an oxidant. In particular, it has proven to be highly effective in oxidizing primary and secondary alcohols to aldehydes and ketones, respectively. The reagent is more selective than the related Jones reagent, so there is little chance of over-oxidation to form carboxylic acids as long as water is not present in the reaction mixture. A typical PCC oxidation involves addition of an alcohol to a suspension of PCC in dichloromethane. The general reaction is:
- 2 [C5H5NH][CrO3Cl] + 3 R2CHOH → 2 [C5H5NH]Cl + Cr2O3 + 3 R2C=O + 3 H2O
Using other common oxidants in the place of PCC usually leads to dehydration, because such alcohols cannot be oxidized directly.
Other more convenient or less toxic reagents for oxidizing alcohols include dimethyl sulfoxide, which is used in Swern and Pfitzner–Moffatt oxidations, and hypervalent iodine compounds, such as the Dess–Martin periodinane.
One disadvantage to the use of PCC is its toxicity, which it shares with other hexavalent chromium compounds.
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- Killoran, Patrick M.; Rossington, Steven B.; Wilkinson, James A.; Hadfield, John A. (2016). "Expanding the scope of the Babler–Dauben oxidation: 1,3-oxidative transposition of secondary allylic alcohols" (in en). Tetrahedron Letters 57 (35): 3954–3957. doi:10.1016/j.tetlet.2016.07.076. https://linkinghub.elsevier.com/retrieve/pii/S0040403916309340.
- Tojo, G.; Fernández, M. (2006). Tojo, G.. ed. Oxidation of Alcohols to Aldehydes and Ketones: A Guide to Current Common Practice. Basic Reactions in Organic Synthesis. New York: Springer. ISBN 978-0-387-23607-0.
- IARC Monographs Supplement 7, Chromium and Chromium Compounds
- History of PCC
- National Pollutant Inventory, Chromium(VI) Compounds Fact Sheets
Original source: https://en.wikipedia.org/wiki/Pyridinium chlorochromate. Read more