Oxidation of Alcohols
Preparation of Adipic Acid
Oxidation of an organic compound commonly involves either increasing its oxygen content or decreasing its hydrogen content. The most common oxidizing agents are potassium permanganate KMnO4 and chromic acid H2CrO4. Primary alcohols are oxidized initially to aldehydes then further to carboxylic acids. Secondary alcohols are oxidized to ketones and oxidation of both primary and secondary alcohols with chromic acid occurs by way of the chromate ester as shown below: [pic]
Tertiary alcohols resist oxidation under mild conditions because they lack a hydrogen atom attached to the carbinol carbon. Chromic acid can therefore distinguish tertiary alcohols from primary and secondary ones. Below is the general equation for the oxidation of a secondary alcohol using potassium dichromate in acid:
Under more drastic conditions, both secondary and tertiary alcohols undergo oxidative cleavage of C-C bonds to give carboxylic acids. Cyclohexanone is a secondary alcohol which may be oxidized with chromic acid to cyclohexanone. More drastic oxidation (higher concentration of dichromate and higher temperature) converts cyclohexanone to adipic acid, a diacid with the same number of carbon atoms as that in cyclohexanol. Adipic acid is an important industrial chemical which is used in the synthesis of polymers.
1- Prepare the oxidant as follows:
Dissolve 8 g of sodium dichromate dihydrate in 15 mL water in a 50 mL Erlenmeyer flask. Cool the resulting solution in an ice-bath and slowly add 5 mL of concentrated sulfuric acid with continuous stirring. 2- In a 250 mL Erlenmeyer flask, introduce 15 mL of water, and slowly add 5 mL of concentrated sulfuric acid. Cool in ice and add, in portions, 2 mL (0.019 mol) of cyclohexanol with stirring. 3- Remove the cyclohexanol solution from the ice bath and start the oxidation by adding a small portion of the...
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