Organic Chemistry Experiment 3: Chromic Acid Oxidation Reaction

Organic chemistry II

Experiment 3: chromic acid oxidation reaction

Introduction:

Camphor is very compact and its molecular structure is symmetrical which gives it the property to change directly from a solid to vapour when heated. Therefore, camphor can easily be purified by sublimation technique. Sublimation is a phase change in which a solid phase passes directly into the vapour without going through an intermediate liquid phase. Solids which have vapour pressure below melting points can be purified by 1) heating the solid to sublime it 2) condensing the vapour on a cold surface 3) scraping off the condensed solid. Sublimation is not a very accurate method as recrystallization or chromatography. The advantages of sublimation technique is

Camphor is a ketone. In the experiment we also need to determine the purity of the product. Ketones can be oxidized from a secondary alcohol using a strong oxidizing agent such as chromic acid. However, there exists chromium compounds that are known to be corrosive and generally harmful and pose as a legal disposal issue due to their harmful nature.

Chromic acid cleanly oxidizes secondary alcohols to ketones using acetones as solvent and the product isolation is simple. The terpene borneol (with an endo-secondary hydroxyl group, -OH) is oxidized to camphor as below: Oxidation of borneol is an exothermic reaction, in order to avoid creation of side product; the experiment should be carried out at room temperature. Extreme heat will lead to creation of camphoric acid, therefore the heat should be controlled when carrying out the experiment.

Result and calculation:

Chromic acid is added continuously until a slight brownish colour solution persists, this is to make sure that complete oxidation of borneol in the experiment. Light petroleum was used to dissolve and extract the product from the aqueous layer twice, 15 mL each. Sodium carbonate and saturated solution were used to wash product and separate both aqueous and organic layer in the separating funnel. This is to increase the accuracy when flowing out the aqueous layer. The extracted organic layer was steam bathed to vaporize light petroleum which has low boiling point at 30-40˚C.

Chromic acid is a more commonly used reagent for the oxidation of alcohols, it is a suspected carcinogen and generates hazardous waste. In green chemistry, innocuous chemical such as hypochlorous acid, HOCl will be used in oxidation, as to reduce the harmful waste. Green chemistry is the name given to modifications implemented in chemical manufacturing processes that ensure a safer and cleaner