Pyridinium chlorochromate

| Ball-and-stick model of the pyridinium cation | Ball-and-stick model of the chlorochromate anion

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Names
IUPAC name

Pyridinium chlorochromate

Other names

PCC; Corey-Suggs reagent

Identifiers

CAS Number

* 26299-14-9 Y

3D model (JSmol)

* Interactive image

ChEBI |

* CHEBI:176795

ChemSpider |

* 10608386 Y

EC Number |

* 247-595-5

PubChem CID

* 129695875

UNII |

* DTV5HU1N27 Y

InChI

* InChI=1S/C5H5N.ClH.Cr.3O/c1-2-4-6-5-3-1;;;;;/h1-5H;1H;;;;/q;;+1;;;-1 N

Key: LEHBURLTIWGHEM-UHFFFAOYSA-N N

* InChI=1/C5H5N.ClH.Cr.3O/c1-2-4-6-5-3-1;;;;;/h1-5H;1H;;;;/q;;+1;;;-1/rC5H5N.ClCrO3/c1-2-4-6-5-3-1;1-2(3,4)5/h1-5H;/q;-1/p+1

Key: LEHBURLTIWGHEM-YOEUSAHMAN

SMILES

* C1=CC=[NH+]C=C1.[O-][Cr](=O)(=O)Cl

Properties

Chemical formula

| 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 in acetone, acetonitrile, THF
Hazards
Main hazards | Toxic, oxidizer, carcinogenic, strong environmental pollutant
Safety data sheet | external SDS
GHS pictograms |
GHS Signal word | Danger

GHS hazard statements

| H272, H317, H350, H410

GHS precautionary statements

| P201, P280, P273, P221, P308+313, P302+352
NFPA 704 (fire diamond)  |

[2]

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

N verify (what is YN ?)
Infobox references

Tracking categories (test):

* SizeSet

Pyridinium chlorochromate in a vial

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.[1]

## Contents

* 1 Structure and preparation
* 2 Uses
* 2.1 Oxidation of alcohols
* 2.2 Babler oxidation
* 2.3 Other reactions
* 3 Related reagents
* 4 Safety
* 5 See also
* 6 References
* 7 Further reading
* 8 External links

## 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.

PCC is commercially available. Discovered by accident,[3] the reagent was originally prepared via addition of pyridine into a cold solution of chromium trioxide in concentrated hydrochloric acid:[4]

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.[5]

## Uses

### 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 if acidified potassium 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 in dichloromethane.[6][7][8] The general reaction is:

2 [C5H5NH][CrO3Cl] + 3 R2CHOH → 2 [C5H5NH]Cl + Cr2O3 \+ 3 R2C=O + 3 H2O

For example, the triterpene lupeol was oxidized to lupenone:[9]

### Babler oxidation

With tertiary alcohols, the chromate ester formed from PCC can isomerize via a [3,3]-sigmatropic reaction and following oxidation yield an enone, in a reaction known as the Babler oxidation:

The Babler-Dauben oxidation of cyclic tertiary allylic alcohols to cyclic enones using PCC.

This type of oxidative transposition reaction has been synthetically utilized, e.g. for the synthesis of morphine.[10]

Using other common oxidants in the place of PCC usually leads to dehydration, because such alcohols cannot be oxidized directly.

### Other reactions

PCC also converts suitable unsaturated alcohols and aldehydes to cyclohexenones. This pathway, an oxidative cationic cyclization, is illustrated by the conversion of (−)-citronellol to (−)-pulegone.

PCC also effects allylic oxidations, for example, in conversion of dihydrofurans to furanones.[1]

## Related reagents

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.

## Safety

One disadvantage to the use of PCC is its toxicity, which it shares with other hexavalent chromium compounds.

## See also

* Oxidation with chromium(VI)-amine complexes
* Babler oxidation

## References

1. ↑ 1.0 1.1 1.2 Piancatelli, G.; Luzzio, F. A. (2007). "Pyridinium Chlorochromate". e-EROS Encyclopedia of Reagents for Organic Synthesis. John Wiley & Sons. doi:10.1002/9780470842898.rp288.pub2. ISBN 978-0471936237.
2. ↑ "Safety Data Sheet". 2015. http://www.acros.com/Ecommerce/msds.aspx?PrdNr=18367&Country=US&Language=en.
3. ↑ Lowe, Derek. "The Old Stuff". Science. https://www.science.org/content/blog-post/old-stuff.
4. ↑ Corey, E. J.; Suggs, J. W. (1975). "Pyridinium Chlorochromate. An Efficient Reagent for Oxidation of Primary and Secondary Alcohols to Carbonyl Compounds". Tetrahedron Letters 16 (31): 2647–2650. doi:10.1016/S0040-4039(00)75204-X.
5. ↑ Agarwal, S.; Tiwari, H. P.; Sharma, J. P. (1990). "Pyridinium Chlorochromate: An Improved Method for Its Synthesis and Use of Anhydrous Acetic Acid as Catalyst for Oxidation Reactions". Tetrahedron 46 (12): 4417–4420. doi:10.1016/S0040-4020(01)86776-4.
6. ↑ Paquette, L. A.; Earle, M. J.; Smith, G. F. (1996). "(4R)-(+)-tert-Butyldimethylsiloxy-2-cyclopenten-1-one". Organic Syntheses 73: 36. http://www.orgsyn.org/demo.aspx?prep=cv9p0132. ;  Collective Volume, 9, pp. 132
7. ↑ Tu, Y.; Frohn, M.; Wang, Z.-X.; Shi, Y. (2003). "Synthesis of 1,2:4,5-Di-O-isopropylidene-D-erythro-2,3-hexodiulo-2,6-pyranose. A Highly Enantioselective Ketone Catalyst for Epoxidation". Organic Syntheses 80: 1. http://www.orgsyn.org/demo.aspx?prep=v80p0001.
8. ↑ White, J. D.; Grether, U. M.; Lee, C.-S. (2005). "(R)-(+)-3,4-Dimethylcyclohex-2-en-1-one". Organic Syntheses 82: 108. http://www.orgsyn.org/demo.aspx?prep=v82p0108. ;  Collective Volume, 11, pp. 100
9. ↑ Lao, A.; Fujimoto, Y.; Tatsuno, T. (1984). "Studies on the Constituents of Artemisia argyi Lévl & Vant". Chemical and Pharmaceutical Bulletin 32 (2): 723–727. doi:10.1248/cpb.32.723. https://www.jstage.jst.go.jp/article/cpb1958/32/2/32_2_723/_article. Retrieved 2016-06-05.
10. ↑ 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.

## Further reading

* 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.

## External links

* IARC Monographs Supplement 7, Chromium and Chromium Compounds
* History of PCC
* National Pollutant Inventory, Chromium(VI) Compounds Fact Sheets

* v
* t
* e

Chromium compounds

Chromium(0)|

* Cr(CO)6

| Organochromium(0) compounds|

* Cr(C6H6)2
* CrC6H6(CO)3

|

Chromium(II)|

* Cr(C2H3O2)2
* CrBr2
* Cr3C2
* Cr(C2O4)
* CrCl2
* CrF2
* CrO
* CrSe
* CrSi2
* CrSO4

| Organochromium(II) compounds|

* Cr(C5H5)2

|

Chromium(II, III)|

* Cr3C2

Chromium(III)|

* Cr(C2H3O2)3
* CrB
* CrBr3
* CrCl3
* CrF3
* CrI3
* CrN
* Cr(NO3)3
* Cr(OH)3
* Cr2O3
* Cr2S3
* Cr2(SO4)3
* Cr2Te3

Chromium(IV)|

* CrCl4
* CrF4
* CrO2

Chromium(V)|

* CrF5
* K3Cr(O2)4

Chromium(VI)|

* CrO3
* CrS3
* CrO(O2)2
* H2CrO4/H2Cr2O7
* CrO2F2
* CrO2Cl2
* C5H5NHCrO3Cl
* CrF6 (hypothetical)

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*[CID]: Compound ID
*[H272]: May intensify fire: oxidizer
*[H317]: May cause an allergic skin reaction
*[H350]: May cause cancer
*[H410]: Very toxic to aquatic life with long lasting effects
*[P201]: Obtain special instructions before use
*[P280]: Wear protective gloves/protective clothing/eye protection/face protection
*[P273]: Avoid release to the environment
*[P221]: Take any precaution to avoid mixing with combustibles
*[P308+313]: IF exposed or concerned: Get medical advice/attention
*[P302+352]: IF ON SKIN: Wash with soap and water
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