Dipyridine Chromium(VI) Oxide

Abstract

[26412-88-4] C10H10CrN2O3 (MW 258.22) InChI = 1S/2C5H5N.Cr.3O/c2*1-2-4-6-5-3-1;;;;/h2*1-5H;;;;/q;;+2;;2*-1 InChIKey = LYUSQVMBCUPELV-UHFFFAOYSA-N (reagent for oxidizing alcohols to carbonyl compounds) Alternate Names: Collins reagent; chromium(VI) oxide–pyridine. Solubility: sol CH2Cl2; (Z)-1,2-dichloroethylene; pyridine; CHCl3. Form Supplied in: red crystals; not commercially available. Preparative Methods: prepared in 85–91% yield from Chromium(VI) Oxide and Pyridine.2, 3 Caution: the reaction is extremely exothermic. The chromium(VI) oxide should be added to dry pyridine at such a rate that the temperature does not exceed 20 °C and in such a way that the oxide mixes rapidly with pyridine. Other chromium(VI) oxide–pyridine complexes are known. These include the Ratcliffe reagent (dipyridine chromium(VI) oxide prepared in situ in CH2Cl2),4, 5 and the Sarett reagent (CrO3·(C5H5N)2 in pyridine).6 The preparation and workup of the Sarett reagent is sometimes tedious. The hygroscopic nature of the Collins reagent and its propensity to inflame may be avoided by the in situ preparation of the complex according to the Ratcliffe procedure. Handling, Storage, and Precautions: Caution: the Collins reagent is extremely hygroscopic; exposure to moisture rapidly converts it to the yellow dipyridinium dichromate. The reagent should be stored at 0 °C under nitrogen or argon in a sealed container, protected from light. All chromium(VI) reagents must be handled with care; their mutagenicity is well documented.7 This reagent should be prepared and handled in a fume hood.