1.3.1 Introduction
Chromium is the 21st most abundant element in Earth's crust with atomic number 24. Naturally occurring chromium composed of three stable isotopes; 52Cr, 53Cr and 54Cr with 52Cr being most abundant. It has an electronic configuration of 3d5 4s1 and exhibits a wide range of oxidation states, where the +3 and +6 states are commonly observed. This section describes some of the important chromium mediated/catalyzed oxidation of organic substrates.
1.3.2 Chromic Acid Oxidation (Jones oxidation)
The combination of CrO3 and sulfuric acid is often referred as Jones reagent, and the oxidation of alcohols with this reagent in acetone is called Jones oxidation. The reagent is selective as it is useful for the oxidation of alcohols, which contain carbon-carbon double or triple bonds, allylic or benzylic C-H bonds (Scheme 1). The reaction is carried at 0-20°C to give the corresponding carbonyl compounds. .
F. Freeman, Encylopedia of Reagents for Organic Synthesis, John Wiley and Sons, Inc., L. A. Paquette, Ed., New York, 1995, 2, 1261. |
 |
Scheme 1 |
Mechanism
In aqueous acid, CrO3 forms chromic acid, which oxidizes the alcohols to carbonyl compounds (Scheme 2).
 |
Scheme 2 |