1. Preparation of Diphenylmethanol by Reduction of Benzophenone
Experiment 16
Preparation of Diphenylmethanol by Reduction of Benzophenone

2. Objectives
Gain experience in preparative reduction of an organic compound
To use TLC to assess the purity of your synthesized product
To gain experience in using mole quantities in calculating % yield

3. Reactions of Alcohols

4. Oxidation of 1° Alcohols
One of the most valuable reactions
Can be accomplished by a large number of oxidizing agents
Certain reagents oxidize too rapidly for the aldehyde to be isolated

5. Reduction to Alcohols
Aldehydes, ketones and carboxylic acids can all be reduced to give 1° and 2° alcohols
Carboxylic acids can be reduced using BH3/THF or LiAlH3
Aldehydes and ketones by NaBH4 or LiAlH3

6. Hydride Reagents Act as a source of nucleophilic hydrogen
Carbonyl carbons are electrophilic
Readily attacked by hydride reagents

7. Safety Notes
Sodium Borohydride – irrirtant, corrosive, toxic and highly reactive with water – gives off highly flammable gas
Dichloromethane is toxic
Benzophenone irritating to the eyes and respiratory system

8. Experimental Dissolve 0.4 g of benzophenone in 7ml of ethanol
Dissolve 0.16 g of NaBH4 in 2ml of cold water in a separate flask
Add the hydride solution dropwise to the benzophenone solution
Allow to react at room temperature for 30 mins – shaking occasionally

9. Experimental
Pour the reaction mixture on to 15ml of ice water and 1ml conc HCl – gas is liberated
Allow to react for a few minutes then isolate the white precipitate on a Hirsch funnel – wash with cold water
Dry on the funnel for 15 mins
Leave to dry in your locker

10. Experimental Check the purity of your product by TLC
Dissolve 10 mg of the crude product in a few drops of dicloromethane
Spot this solution on to a TLC plate along with a reference solution of benzophenone
Develop the plate in 10% ethyl acetate/hexane
Visualise the plate by staining with iodine

11. TLC plate
Ideally, the spot from your crude crystals should not contain any benzophenone
The reference spot of starting material allows for comparison
Based on the TLC make a conclusion about the purity of your product

12. Report Calculate the % yield of alcohol product
Use numbers of moles of starting material and product in calculations
Melting point of your product
Calculate Rf values of starting matereial and product
Intro, discussion & question in manual