Oxidation with chromium(VI) complexes: Difference between revisions

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

AllOne family of these reagents consist ofemploys the complex CrO₃(pyridine)₂.<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>

*Sarrett's reagent: a solution of CrO₃(pyridine)₂ in pyridine. It was popularized for selective oxidation of primary and secondary alcohols to carbonyl compounds.<ref>Poos, G. I.; Arth, G. E.; Beyler, R. E.; Sarrett, L. H. ''J. Am. Chem. Soc.'', '''1953''', ''75'', 422.</ref> showed that pyridine reacts with CrO₃ in

*[[Collins reagent]] is a solution of CrO₃(pyridine)₂ in dichloromethane. The Ratcliffe variant of Collins reagent relates to details of the preparation of this solution, i.e., the addition of chromium trioxide to a solution of pyridine in methylene chloride.

The reagentssecond pyridiniumfamily dichromateof and pyridinium chlorochromatereagents are ''salts'', featuring the pyridinium cation (C₅H₅NH⁺).
*[[pyridinium dichromate]] is the pyridium salt of [C₂rO₇]^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==