Pyridinium chlorochromate
General
Systematic name	Pyridinium Chlorochromate
Synonum	PCC
Molecular formula	C5H5NHClCrO3
Molar mass	215.56 g/mol
Appearance	orange crystalline powder
CAS number	26299-14-9
Properties
Melting point	205 °C
Solubility	soluble in dichloromethane, benzene, diethyl ether, sol acetone, acetonitrile, THF
Hazards
MSDS	external MSDS sheet
Main hazard	oxidizing, toxic, flammable carcinogenic, irritant
NFPA 704	Image File history File links Pyridinium_chlorochromate. ... Image File history File links Size of this preview: 530 × 600 pixel Image in higher resolution (972 × 1100 pixel, file size: 138 KB, MIME type: image/png) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Pyridinium chlorochromate ... Image File history File links Size of this preview: 546 × 600 pixel Image in higher resolution (1001 × 1100 pixel, file size: 119 KB, MIME type: image/png) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Pyridinium chlorochromate ... IUPAC nomenclature is a system of naming chemical compounds and of describing the science of chemistry in general. ... A chemical formula (also called molecular formula) is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... Molar mass is the mass of one mole of a chemical element or chemical compound. ... CAS registry numbers are unique numerical identifiers for chemical compounds, polymers, biological sequences, mixtures and alloys. ... The melting point of a crystalline solid is the temperature at which it changes state from solid to liquid. ... Solubility refers to the ability for a given substance, the solute, to dissolve in a solvent. ... Dichloromethane or Methylene chloride is a chemical compound widely used as a solvent for organic materials. ... Benzene, also known as benzol, is an organic chemical compound with the formula C6H6. ... Diethyl ether, also known as ether and ethoxyethane, is a clear, colorless, and highly flammable liquid with a low boiling point and a characteristic smell. ... In chemistry, acetone (also known as propanone, dimethyl ketone, 2-propanone, propan-2-one and β-ketopropane) is the simplest representative of the ketones. ... Acetonitrile is an organic molecule, often used as a solvent, with the chemical formula of CH3CN. Also known as methyl cyanide, it is the simplest of the organic nitriles. ... Tetrahydrofuran, also known as THF, hydrofuran, oxolane, oxacyclopentane, or furanidine, is a heterocyclic organic compound. ... An example MSDS in a US format provides guidance for handling a hazardous substance and information on its composition and properties. ... The examples and perspective in this article or section may not represent a worldwide view. ... NFPA 704 is a standard maintained by the U.S. National Fire Protection Association. ... Image File history File links NFPA_704. ... 0 3 3
R/S statement	R: 49-8-43-50/53 S: 53-45-60-61

Pyridinium chlorochromate, a reddish orange solid reagent, is used to oxidize primary alcohols to aldehydes and secondary alcohols to ketones. Pyridinium chlorochromate, or PCC, will not fully oxidize the alcohol to the carboxylic acid as does the Jones reagent. A disadvantage to using PCC is its toxicity. PCC was developed by Elias James Corey and William Suggs in 1975. Risk and Safety Statements, also known as R/S statements, R/S numbers, R/S phrases, and R/S sentences, is a system of hazard codes and phrases for labeling dangerous chemicals and compounds. ... R-phrases are defined in Annex III of European Union Directive 67/548/EEC: Nature of special risks attributed to dangerous substances and preparations. ... S-phrases are defined in Annex IV of European Union Directive 67/548/EEC: Safety advice concerning dangerous substances and preparations. ... To oxidize an element or a compound is to increase its oxidation number. ... In general usage, alcohol (from Arabic al-khwl الكحول, or al-ghawl الغول) refers almost always to ethanol, also known as grain alcohol, and often to any beverage that contains ethanol (see alcoholic beverage). ... An aldehyde is either a functional group consisting of a terminal carbonyl group, or a compound containing a terminal carbonyl group. ... In general usage, alcohol (from Arabic al-khwl الكحول, or al-ghawl الغول) refers almost always to ethanol, also known as grain alcohol, and often to any beverage that contains ethanol (see alcoholic beverage). ... A ketone is either the functional group characterized by a carbonyl group linked to two other carbon atoms or a compound that contains this functional group. ... Structure of a carboxylic acid The 3D structure of the carboxyl group A space-filling model of the carboxyl group Carboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the formula -C(=O)OH, usually written -COOH or -CO2H. [1] Carboxylic acids are Bronsted... In chemistry, chromic acid (or Jones reagent) is a chromium (Cr) compound, yet to be isolated, that would have the formula H2CrO4. ... Elias James Corey (born July 12, 1928) is an American organic chemist. ... 1975 (MCMLXXV) was a common year starting on Wednesday. ...

Pyridinium dichromate or PDC is a similar oxidizing agent with chemical formula (C₅H₅NH)₂Cr₂O₇. In this compound chromium is present as the dichromate ion. PDC presents the advantage of being less acidic than PCC. European Union Chemical hazard symbol for oxidizing agents Dangerous goods label for oxidising agents An oxidizing agent (also called an oxidant or oxidizer) is referred to as A chemical compound that readily transfers oxygen atoms or A substance that gains electrons in a redox chemical reaction. ... General Name, Symbol, Number chromium, Cr, 24 Chemical series transition metals Group, Period, Block 6, 4, d Appearance silvery metallic Atomic mass 51. ... Chromates and Dichromates are salts of chromic acid. ...

Preparation

The original preparation by Corey involves adding one equivalent of pyridine to a solution of one equivalent of chromium(VI) trioxide and concentrated hydrochloric acid: Pyridine is a chemical compound with the formula C5H5N. It is a liquid with a distinctively putrid odour. ... In chemistry, chromic acid is a chromium (Cr) compound, yet to be isolated, with the formula H2CrO4. ... The chemical compound hydrochloric acid is the aqueous (water-based) solution of hydrogen chloride gas (HCl). ...

C₅H₅N + HCl + CrO₃ → [C₅H₅NH][CrO₃Cl]

Agarwal et al. presented an alternative synthesis that avoids the harmful side product chromyl chloride (CrO₂Cl₂). Chromium(VI) oxide pyridinium chloride: Pyridine is a chemical compound with the formula C5H5N. It is a liquid with a distinctively putrid odour. ...

[C₅H₅NH⁺]Cl^- + CrO₃ → [C₅H₅NH][CrO₃Cl]

Properties and uses

PCC is primarily used as an oxidant. In particular, it has proven to be highly effective in oxidizing primary and secondary alcohols to aldehydes and ketones, respectively. Rarely does over-oxidation occur (whether intentionally or accidentally) to form carboxylic acids. A typical PCC oxidation involves addition of the alcohol to a suspension of PCC in dichloromethane. A sample reaction would be:
An oxidizing agent is a substance that oxidizes another substance in electrochemistry or redox chemical reactions in general. ... In general usage, alcohol (from Arabic al-khwl الكحول, or al-ghawl الغول) refers almost always to ethanol, also known as grain alcohol, and often to any beverage that contains ethanol (see alcoholic beverage). ... An aldehyde is either a functional group consisting of a terminal carbonyl group, or a compound containing a terminal carbonyl group. ... A ketone is either the functional group characterized by a carbonyl group linked to two other carbon atoms or a compound that contains this functional group. ... In chemistry, carboxylic acids (also called alkanoic acids) are organic acids characterized by the presence of a carboxyl group. ...

2 C₅H₅NHCrO₃Cl + 3 R₂CHOH → 2 C₅H₅NHCl + "CrO_1.5" + 3 R₂C=O + 3 H₂O

In practice the chromium byproduct deposits with pyridine as a sticky black tar, which can complicate matters. Addition of an inert adsorbent such as crushed molecular sieves allows the sticky byproduct to adsorb to the surface, and makes workup easier.

PCC is also remarkable for its high selectivity. For example, when oxidizing tertiary allyl alcohols, unsaturated aldehydes are observed as the sole product. Otherwise such oxidations commonly afford dienes as by-products resulting from dehydration.
An allyl group is an alkene hydrocarbon group with the formula H2C=CH-CH2-. It is made up of a vinyl group, CH2=CH-, attached to a methylene -CH2. ... An aldehyde. ...

Another notable oxidative reaction of PCC is its efficient conversion of unsaturated alcohols or aldehydes to cyclohexenones. This particular pathway is known as oxidative cationic cyclization. A cation is an ion with positive charge. ...

Controversy

PCC is controversial as it contains chromium(VI). More environmentally friendly oxidants listed above are therefore favored by green chemists. Other methods for oxidizing alcohols using less toxic reagents have been introduced: Chromium hexavalent Cr(VI) compounds, often called hexavalent chromium, exist in several forms. ... An oxidizing agent is a compound that oxidizes another substance in electrochemistry or redox chemical reactions. ... Green chemistry is a chemical philosophy encouraging the design of products and processes that reduce or eliminate the use and generation of hazardous substances. ... In general usage, alcohol (from Arabic al-khwl الكحول, or al-ghawl الغول) refers almost always to ethanol, also known as grain alcohol, and often to any beverage that contains ethanol (see alcoholic beverage). ...

• DMSO-based oxidations (Swern oxidation, Moffatt oxidation)
• hypervalent iodine based oxidation (such as the Dess-Martin periodinane)

Dimethyl sulfoxide (DMSO) is the chemical compound (CH3)2SO. This colorless liquid is an important dipolar aprotic solvent. ... The mild oxidation of primary or secondary alcohols to aldehydes or ketones with a mixture of oxalyl chloride, dimethylsulfoxide and triethylamine is called the Swern oxidation. ... The Pfitzner-Moffatt oxidation, sometimes referred to as simply the Moffatt oxidation, is a chemical reaction which describes the oxidation of primary and secondary alcohols by dimethyl sulfoxide (DMSO) activated with a carbodiimide, such as dicyclohexylcarbodiimide (DCC). ... Periodinanes are chemical compounds containing hypervalent iodine. ... The Dess-Martin periodinane is a chemical reagent used to oxidize alcohols to aldehydes and ketones. ...

References

• Agarwal, S, Tiwari, H. P., Sharma, J. P., 'Pyridinium Chlorochromate: an Improved Method for its Synthesis and use of Anhydrous acetic acid as catalyst for oxidation reactions', Tetrahedron (journal) 1990, 46, 4417-4420.
• Corey, E.J., and Suggs, W. 'Pyridinium Chlorochromate. An Efficient Reagent for Oxidation of Primary and Secondary Alcohols to Carbonyl Compounds', Tetrahedron Lett. 1975, 16, 2647-2650.
• Paquette, L. A.; Earle, M. J.; Smith, G. F. Organic Syntheses, Coll. Vol. 9, p.132 (1998); Vol. 73, p.36 (1996). (Article)
• Piancatelli, G. 'Pyridinium Chlorochromate', Encyclopedia of Reagents for Organic Synthesis 2001. (Article)
• Tu, Y.; Frohn, M.; Wang, Z.-X.; Shi, Y. Organic Syntheses, Vol. 80, p.1 (2003). (Article)
• White, J. D.; Grether, U. M.; Lee, C.-S. Organic Syntheses, Vol. 82, p.108 (2005). (Article)

Tetrahedron is an international journal publishing full origonal research papers in the field of organic chemistry. ... Tetrahedron Letters is a weekly international journal for rapid publication of full origonal research papers in the field of organic chemistry. ... Organic Syntheses is a scientific journal that Since 1921 has provided the chemistry community with annual collections of detailed and checked procedures for the organic synthesis of organic compounds. ... Organic Syntheses is a scientific journal that Since 1921 has provided the chemistry community with annual collections of detailed and checked procedures for the organic synthesis of organic compounds. ... Organic Syntheses is a scientific journal that Since 1921 has provided the chemistry community with annual collections of detailed and checked procedures for the organic synthesis of organic compounds. ...

External links

• IARC Monograph "Chromium and Chromium compounds"
• History of PCC
• Datasheet PDC
• National Pollutant Inventory - Chromium VI and compounds fact sheet