PCC chemistry reagent

Pyridinium chlorochromate (PCC) is an oxidizing agent which can oxidized alcohols to aldehydes and ketones.

PCC is formed from the reaction between pyridinechromium trioxide, and hydrochloric acid. Chlorochromatic acid can be prepared by the dissolution of chromium trioxide in aqueous hydrochloric acid. Addition of pyridine gives pyridinium chlorochromate as orange crystals.

The properties of PCC:

  • It is not particularly hygroscopic
  • It is stable
  • Commercially available
  • It can be stored
  • It is soluble in many organic solvents (especially in dichloromethane at room temperature).

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

PCC oxidizes primary alcohols to aldehydes and secondary alcohols to ketones. Unlike chromic acid, PCC will not oxidize aldehydes to carboxylic acids. A variety of related compounds are known with similar reactivity. Although no longer widely used, PCC offers the advantage of the selective oxidation of alcohols to aldehydes or ketones, whereas many other reagents are less selective.

The mechanisms for these reactions are the same and consist of four steps. We can see them on the above-marked pages.

These reactions of this sort are actually a kind of elimination reaction. We are going from a carbon-oxygen single bond to a carbon-oxygen double bond which means that two groups are eliminated. This is achieved if we have a good leaving group attached to oxygen or chromium. This leaving group will be displaced when the neighboring carbon-oxygen bond is broken with a base.

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