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.]]'' '''|year=1998''', ''|volume=53'', |page=1. {{|doi|=10.1002/0471264180.or053.01}}</ref>

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

One family of reagents employs the complex CrO₃(pyridine)₂.<ref>{{cite journalbook |doi=10.1007/0-387-25725-X_1|tielchapter=Chromium-based Reagents|title=Oxidation of Alcohols to Aldehydes and Ketones|journalseries=OrganicBasic Reactions in Organic Synthesis|year=2006|pages=1–95|isbn=0-387-23607-4}}</ref>

*[[Sarett oxidation|Sarett's reagent]]: a solution of CrO₃(pyridine)₂ in pyridine. It was popularized for selective oxidation of primary and secondary alcohols to carbonyl compounds.

*[[Collins reagent]] is a solution of the same CrO₃(pyridine)₂ but 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>

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==Practical considerations==

Oxidation with chromium(VI) amines has two primary limitations. Operationally, the tarry byproducts of chromium oxidations cause reduced yields and product sequestration.<ref>Ratcliffe, R.; Rodehorst, R. ''J. Org. Chem.'', '''1970''', ''35'', 4000.</ref> In addition, Cr(VI)-amines (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>

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==Historic references==

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

*{{cite journal | title = Improved Procedure for Oxidations with the Chromium Trioxide-Pyridine Complex| author = Ronald Ratcliffe and Ronald Rodehorst | journal = [[J. Org. Chem.]] | year = 1970 | volume = 35 | issue = 11 | pages = 4000–4001 | doi = 10.1021/jo00836a108}}

==References==

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