Oxidation with chromium(VI) complexes: Difference between revisions

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

One family of reagents employs 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 the same 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.<ref name=JCC>{{cite journal | author = J. C. Collins, W.W. Hess | title = Aldehydes from Primary Alcohols by Oxidation with Chromium Trioxide: Heptanal | volume = 52 | pages = 5 | doi = 10.15227/orgsyn.052.0005 | year = 1972}}</ref>

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

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Catalytic methods employing cheap, clean terminal oxidants in conjunction with catalytic amounts of chromium reagents produce only small amounts of metal byproducts.<ref>Muzart, J. ''Tetrahedron Lett.'', '''1987''', ''28'', 2133.</ref> However, undesired side reactions mediated by stoichiometric amounts of the terminal oxidant may occur.

==Historic references==

*Poos, G. I.; Arth, G. E.; Beyler, R. E.; Sarrett, L. H. ''J. Am. Chem. Soc.'', '''1953''', ''75'', 422.

==References==