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| Names | |||
|---|---|---|---|
| IUPAC name Pyridinium chlorochromate | |||
| Other names PCC; Corey-Suggs reagent | |||
| Identifiers | |||
3D model (JSmol) | |||
| ChEBI | |||
| ChemSpider |
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| ECHA InfoCard | 100.043.253 | ||
| EC Number |
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| UNII | |||
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| Properties | |||
| C5H6ClCrNO3 | |||
| Molar mass | 215.56 g/mol | ||
| Appearance | yellow-orange solid[1] | ||
| Melting point | 205 °C (401 °F; 478 K) | ||
| Solubility in other solvents | soluble inacetone,acetonitrile,THF | ||
| Hazards | |||
| Occupational safety and health (OHS/OSH): | |||
Main hazards | Toxic, oxidizer, carcinogenic, strong environmental pollutant | ||
| GHS labelling: | |||
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| Danger | |||
| H272,H317,H350,H410 | |||
| P201,P221,P273,P280,P302+P352,P308+P313 | |||
| NFPA 704 (fire diamond) | |||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Pyridinium chlorochromate (PCC) is a yellow-orangesalt with theformula [C5H5NH]+[CrO3Cl]−. It is areagent inorganic synthesis used primarily foroxidation ofalcohols to formcarbonyls. 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.[1]
PCC consists of apyridinium cation, [C5H5NH]+, and a tetrahedral chlorochromate anion, [CrO3Cl]−. Related salts are also known, such as 1-butylpyridinium chlorochromate, [C5H5N(C4H9)][CrO3Cl] andpotassium chlorochromate.
PCC is commercially available.Discovered by accident,[3] the reagent was originally prepared via addition ofpyridine into a cold solution ofchromium trioxide in concentratedhydrochloric acid:[4]
In one alternative method, formation of toxicchromyl chloride (CrO2Cl2) fumes during the making of the aforementioned solution were 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.[5]
PCC is used as anoxidant. In particular, it has proven to be highly effective inoxidizing primary and secondary alcohols toaldehydes andketones, respectively. The reagent is more selective than the relatedJones' Reagent, so there is little chance of over-oxidation to formcarboxylic acids if acidifiedpotassium permanganate is used 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 indichloromethane.[6][7][8] The general reaction is:
For example, thetriterpenelupeol was oxidized tolupenone:[9]
With tertiary alcohols, thechromate ester formed from PCC can isomerizevia a[3,3]-sigmatropic reaction and following oxidation yield an enone, in a reaction known as the Babler oxidation:
This type of oxidative transposition reaction has been synthetically utilized,e.g. for the synthesis ofmorphine.[10]
Using other common oxidants in the place of PCC usually leads to dehydration, because such alcohols cannot be oxidized directly.
PCC also converts suitable unsaturated alcohols and aldehydes tocyclohexenones. This pathway, an oxidativecationic cyclization, is illustrated by the conversion of (−)-citronellol to (−)-pulegone.
PCC also effectsallylic oxidations, for example, in conversion ofdihydrofurans tofuranones.[1]
Other more convenient or less toxic reagents for oxidizingalcohols includedimethyl sulfoxide, which is used inSwern andPfitzner–Moffatt oxidations, andhypervalent iodine compounds, such as theDess–Martin periodinane.
One disadvantage to the use of PCC is its toxicity, which it shares with otherhexavalent chromium compounds.
