Oxidation with chromium(VI) complexes: Difference between revisions

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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>

==Inventory of Cr(VI)-pyridine reagents==

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The second family of reagents are ''salts'', featuring the pyridinium cation (C₅H₅NH⁺).

*[[pyridinium dichromate]] is the pyridium salt of dichromate, [CCr₂rOO₇]^2-.

*[[pyridinium chlorochromate]] is the pyridinium salt of [CrO₃Cl]^-.

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.

==Practical considerations==

Oxidation with chromium(VI) amines has two primary limitations. Operationally, the tarry byproducts oflead chromiumto oxidations cause reducedlowered yields and product sequestration. In addition, Cr(VI)-aminessome such reagents (particularly PCC) may react with [[acid]]-labile functionality. Thus, these agents have been employed in oxidations of relatively simple substrates, often in excess to account for reagent trapping and decomposition. The use of adsorbents such as Celite or silica gel facilitates the removal of chromium byproducts and eliminates many of the operational difficulties associated with chromium-mediated oxidations.

<span style="float:right;padding-right:50px;padding-top:30px;">'''''(1)'''''</span><center>[[File:ChroGen.png]]</center>