1.9.4 2-Iodoxybenzoic acid (IBX)

2-Iodoxybenzoic acid (IBX) is an organic compound prepared by oxidation of 2-iodobenzoic acid with potassium bromate in aqueous sulfuric acid. This is used for the oxidation of alcohols to give carbonyl compounds. The only drawback is that it is insoluble in common organic solvents but soluble in highly polar solvent such as DMSO.

1.9.4.1 Preparation

The oxidation of 2-iodobenzoic acid in aqueous sulfuric acid with potassium bromate gives IBX (Scheme 1). 

Scheme 1

1.9.4.2 Oxidation of Alcohols

The alcohols are oxidized to aldehydes and ketones when treated with IBX (Scheme 2). The reaction occurs smoothly without affecting other functional groups.

Scheme 2

Mechanism
The oxidation mechanism is similar to that of DMP reaction (Scheme 3).

Scheme 3

1.9.5 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)

Quinones are used for dehydrogenation reactions. Among them, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) is an important reagent. DDQ is very reactive and used under anhydrous conditions because it decomposes in the presence of water. The reaction is carried out in inert solvents such as benzene, THF and dioxane. Solution of DDQ in benzene is red in colour because of the formation of charge transfer complex. After dehydrogenation, DDQ is reduced to hydroquinone that is a yellow solid and insoluble in benzene. Hence, the progress of the dehydrogenation can be monitored.

1.9.5.1 Preparation

DDQ is very convenient to handle and is commercially available. It can be synthesized as described by Thiele and Ganther procedure from the reactions of benzoquinone with HCN/HCL followed by oxidation (Scheme 4).

Scheme 4

D. R. Buckle, Encyclopedia of Reagents for Organic Synthesis, John Wiley and Sons, Inc., L. A. Paquette, Ed., New York, 1995, 3, 1699.