Reduction of acetophenone to 1-phenylethanol
- 1.2 g NaBH4 + 25 mL EtOH (95%)
- dropwise (controlled addition; keep temperature < 50o ) of 12 mL of acetophenone
- let stand 15 minutes
- acidify with 10 mL (3M) HCl
- boil down on hot plate until you have two layers
- extract with (1) 20 mL Et2O
(2) 10 mL Et2O
-dry combined ether extracts over anh. MgSO4 TWICE!
-distill off Et2O (  waste bottle )
-residue = crude product (bp 102.5 – 103.5 @ 19 Torr), do not distill
IR, nmr of product AND acetophenone
We will not purify the product with vacuum distillation. After the removal of the diethyl
ether, package, weigh and label the crude product. Obtain IR and nmr on both the
acetophenone and the product.
Answer the following questions:
1. What was the molar ratio of NaBH4 to acetophenone that you used in the experiment.
What is the theoretical ratio? Why did you use more than the theoretical ratio?
2. After the reaction of the carbonyl with sodium borohydride, the mixture is treated with
water and acid to produce the desired alcohol. Indicate the source of the alcoholic
hydrogen in the product.
3. Although sodium borohydride reacts slowly with methanol, when mineral acid was
added, it rapidly decomposed with the evolution of hydrogen. Explain.
4. Why is 1-phenylethanol more prone to dehydration than 2-phenylethanol?
5. What is the structure of the white precipitate that forms in the reaction of
acetophenone with NaBH4?
6. Write an equation for the reaction of the white ppt with water and HCl.
7. Draw the structure of the products of the reduction of each of the following with
NaBH4:
a) cyclohexanone
b) 3-cyclohexen-1-one
c) 1,4-butanedial
d) 4-oxohexanal
8. Draw the structure of the products for the reduction of each of the compounds in
question 7 with excess hydrogen gas over Nickel.
9. Why does the concentration of the ethanolic reaction mixture, followed by the
addition of HCl, result in the formation of two layers?