Title: Determination of an unknown alcohol by oxidation reaction Objective: To identify the unknown alcohol from reaction product. Materials needed: Round flask, conical bottom flask, Erlenmeyer flask, receiver distilling still, filtering flask, suction glass funnel, condenser, Pasteur pipette, capillary tube, boiling stone, activated carbon, hot plate and heat dissipation block. Chemicals needed: Concentrated sulfuric acid, potassium dichromate, 2, 4-dinitrophenylhydrazine, ethanol, Rosaniline, hydrochloride, and sodium metabisulfite.
Procedure: 1. In a round bottom flask add 1 mL of concentrated sulfuric acid and 5 mL of potassium dichromate, and place in ice water bath to cool for 5 minutes. 2. Add 1 mL of the unknown alcohol, dropwise and stir for 5 minutes. 3. Add 5 mL water, and boiling stone and place a receiver distilling still fitted with a water cooled condenser. Perform distillation. 4. If two layers are seen, remove lower layer using pastuer pipette. 5. Add 3 drops of distilled liquid to the upper layer and 2 mL of water in test tube. To this add 1 mL of schiffs reagent, mix and observe the color change. 6. Add 5 mL of 2,4-dinitrophenylhydrazine in a conical bottom flask. 7. Add 1 ml of distilled liquid into the conical bottom flask, place a stopper on top and shake. Observe for a precipitate and place in ice water bath for few minutes. 8. Filter the precipitate by suction filtration. 9. Crystallize the precipitate from 3 mL ethanol.Filter the crystals obtained by suction filtration, then wash for a minute with cool ethanol and continue to suction to air dry the crystals. 10. Determine the melting point and compare to its corresponding 2,4-diphenylhydrazone with other 2,4-diphenylhydrazone listed. Results and Data:
Observations: Unknown solution # 1 Distillation: Clear liquid Transferring upper layer + adding 2 mL water+ 1 mL Schiff reagent in test tube: Distinct pink color. 5 mL of 2, 4-dinitrophenylhydrazine + 1 mL of distilled liquid: orange precipitate Suction filtration: Orange precipitate Melting point: 78˚C Discussion:
To identify organic compounds, direct or indirect experimental methods can be used. For direct experimental method, the organic compound is identified by determining the melting point, boiling point, or elemental analysis. For impure substances, indirect experimental methods are used, and this is done by converting it to the other compound with the reaction that has been known for a suspected existing functional group. An example of indirect experimental method is, aldehydes and ketones can be are oxidized to aldehydes and ketones, which can be converted to corresponding derivatives, which can be defined by direct experimental method. In this experiment, unknown alcohol was determined by converting to aldehyde or ketone then to 2,4diphenylhydrazone derivative. Comparing the melting point of the unknown and comparing it to the melting point of known 2,4-diphenylhydrazone derivative, the unknown alcohol was identified. Conclusion: In conclusion, the boiling point of the unknown alcohol solution #1 was found to be 78˚C, and the alcohol that has a boiling point of 78˚C is ethanol, therefore the unknown alcohol is ethanol. When the upper layer of the distilled liquid was added with 2 mL of water in a test tube and tested with schiffs reagent, there was a distinct pink color which indicates the presence of an aldehyde. The sulfur in the bisulfate ion of the Schiff reagent acts as a nucleophile and adds to the carbonyl carbon, and will only add to a sterically unhindered carbonyl. This rewuires that the carbonyl be part of an aldehyde in which one of the R groups is the very small hydrogen. A
ketone having large groups attached to carbonyl groups will not react with bisulfate.
When 2,4-dinitrophenylhydrazine was added to 1 mL of the distilled liquid, it formed a orange precipitate. Aldehydes and ketones react with 2,4-dinitrophenylhydrazine reagent to form yellow, orange, or reddish-orange precipitates, where the alcohols do not react. The precipitate from this test serves as a solid derivative.
