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'''Oxidation with chromium(VI) complexes''' involves the conversion of alcohols to carbonyl compounds or more highly oxidized products through the action of molecular chromium(VI) oxides and salts.<ref>{{cite journal|author=Luzzio, F. A.|journal=[[Org. React.]]|title=The Oxidation of Alcohols by Modified Oxochromium(VI)–Amine Reagents|year=1998|volume=53|page=1|doi=10.1002/0471264180.or053.01}}</ref> The principal reagents are Collins reagent, PDC, and PCC. These reagents represent improvements over inorganic chromium(VI) reagents such as [[Jones reagent]].
==Inventory of Cr(VI)-pyridine and pyridinium reagents==
Cr(VI)-pyridine and pyridinium reagents have the advantage that they are soluble in organic solvents as are the alcohol substrates.
One family of reagents employs the complex CrO<sub>3</sub>(pyridine)<sub>2</sub>.<ref>{{cite book |doi=10.1007/0-387-25725-X_1|chapter=Chromium-based Reagents|title=Oxidation of Alcohols to Aldehydes and Ketones|series=Basic Reactions in Organic Synthesis|year=2006|pages=1–95|isbn=0-387-23607-4}}</ref>
*[[Sarett oxidation|Sarett's reagent]]: a solution of CrO<sub>3</sub>(pyridine)<sub>2</sub> in pyridine. It was popularized for selective oxidation of primary and secondary alcohols to carbonyl compounds.
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The second family of reagents are ''salts'', featuring the pyridinium cation (C<sub>5</sub>H<sub>5</sub>NH<sup>+</sup>).
*[[pyridinium dichromate]] (PDC) is the pyridium salt of dichromate, [Cr<sub>2</sub>O<sub>7</sub>]<sup>2-</sup>.
*[[pyridinium chlorochromate]] (PCC) is the pyridinium salt of [CrO<sub>3</sub>Cl]<sup>-</sup>.
These salts are less reactive, more easily handled, and more selective than Collins reagent in oxidations of alcohols. These reagents, as well as other, more exotic adducts of nitrogen heterocycles with chromium(VI), facilitate a number of oxidative transformations of organic compounds, including cyclization to form [[tetrahydrofuran]] derivatives and allylic transposition to afford enones from [[allyl]]ic alcohols.
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