3.6.3 Chromium Reagents/Catalysts

Chromium can exist in a variety of oxidation states, Cr(III) and Cr(VI) being the most common of them. These two oxidation states form a redox couple with standard reduction potential of 1.33 V. Thus, Cr(VI) reagents are very strong oxidizing agents.

3.6.1 Oxidation of Alcohols

Chromium(VI) oxide is a very powerful oxidizing agent whose oxidizing power can be tailored by using it in conjunction of a Lewis base like pyridine. CrO₃ when dissolved in H₂ SO₄ forms a mixture of various chromic acids (Jones Reagent). It is a very powerful oxidizing agent capable of oxidizing primary alcohols to carboxylic acids and secondary alcohols to ketones (Scheme 1-2).

Ref: F. Freeman, Encyclopedia of Reagents for Organic Synthesis , John Wiley and Sons, Inc., L. A. Paquette, Ed., New York, 1995, 2 , 1261.

 

Scheme 1

Mechanism

Scheme 2