Pyridinium chlorochromate

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Pyridinium chlorochromate (PCC) is a yellow‑orange salt used in organic synthesis as an oxidant. It combines a pyridinium cation with a chlorochromate anion and is also known as the Corey–Suggs reagent.

What it does
- PCC selectively oxidizes alcohols to carbonyl compounds: primary alcohols to aldehydes and secondary alcohols to ketones.
- It is more selective than Jones’ reagent and can prevent over‑oxidation to carboxylic acids if water is not present in the reaction mixture.

How it’s used
- Typical setup: an alcohol is treated with PCC in dichloromethane.
- The reaction generally stops at the aldehyde or ketone stage, avoiding further oxidation.

Notable reactions and applications
- Primary alcohols to aldehydes and secondary alcohols to ketones without extensive over‑oxidation.
- Babler oxidation: for tertiary alcohols, PCC can promote a [3,3]-sigmatropic rearrangement followed by oxidation to give enones, a route used in complex molecule synthesis (e.g., morphine-related chemistry).
- Oxidative cationic cyclization: unsaturated alcohols and aldehydes can be converted to cyclohexenones (example: (−)-citronellol to (−)-pulegone).
- Allylic oxidations: PCC can oxidize allylic positions, such as converting dihydrofurans to furones.

Related reagents and alternatives
- Other oxidation methods include Swern, Pfitzner–Moffatt, and Dess–Martin periodinane, which can be less toxic or more convenient in some cases.
- Related salts include 1‑butylpyridinium chlorochromate and potassium chlorochromate.

Safety and limitations
- PCC contains hexavalent chromium and is toxic and an environmental pollutant; it must be handled with care and disposed of properly.
- While highly useful, its toxicity is a drawback compared with some alternative oxidants.