Experiment 3 - Reduction of a Ketone
Objective
To learn a versatile reaction for the reduction of a ketone (or aldehyde) to an alcohol.Introduction
The carbonyl group (CO) found in aldehydes, ketones, carboxylic acids, esters, amides and other functional groups, plays a major role in determining the chemistry of these functional groups. This is due to the polar nature of the carbon-oxygen bond and to the presence of the relatively weak pi bond.Figure 1
Equation
Figure 2
Stoichiometry Note
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•Check your lecture textbook or online materials for a discussion of the reaction of sodium borohydride. Each of the four hydrides in NaBH4 is "active" and capable of reducing the carbonyl group of a ketone.
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•How many 'moles' of NaBH4 will be required to reduce one mole of ketone?
Pre-Lab
Complete the pre-lab assignment in WebAssign.Procedure
In a 50 mL Erlenmeyer flask, dissolve about 0.500 g (note the actual amount used) of fluorenone in 8 - 10 mL of methanol. The contents may need to be warmed to completely dissolve the ketone. Quickly weigh between 0.040 g and 0.060 g of sodium borohydride. (NaBH4 absorbs moisture from the atmosphere; therefore, weigh as rapidly (albeit accurately) as possible). Add the solid to the ketone solution in one portion. Swirl vigorously to dissolve. With intermittent swirling, let the reaction mixture stand at room temperature for a period of 15 minutes during which it will turn from yellow to colorless. Add 5 mL of water (solid will form) and heat the reaction mixture to boiling (60°C - 65°C (hot plate)). Occasionally remove the mixture from the hot plate and swirl vigorously. After 5 minutes, remove the mixture from the hot plate and let cool to room temperature. Collect the crude 9-fluorenol via vacuum filtration. Wash the solid with ice-cold 50% aqueous methanol. Allow it to dry (spread the solid out on the tile). Determine the mass and melting point of the product. Also, determine purity of product as well as presence of unreacted starting material by TLC analysis in 7:3 hexane:acetone. The product can be recrystallized from a small amount of 75% aqueous methanol.In-Lab Questions
Download and print the worksheet. You will use this worksheet to record your answers to the In-Lab questions.Questions
Record the following data.- Question 1: Amount of fluorenone ___________________ g, ___________________ mol
- Question 2: Amount of sodium borohydride ___________________ g, ___________________ mol
- Question 3: Amount of hydride ___________________ mol
- Question 4: Theoretical yield of 9-fluorenol ___________________
- Question 5: Show calculations for questions 1 - 4.
- Question 6: Actual yield of 9-fluorenol ___________________ g, ___________________ mol
- Question 7: Percentage yield ___________________
- Question 8: Melting point of 9-fluorenol ________________ (observed), ________________ (reported)
- Question 9: Rf values: Fluorenone ___________________ , 9-fluorenol ___________________