Question

1. Use Figure 8.3 answer the following:

a. Why is it necessary to form the free base before reducing with sodium borohydride?

b. What was the reaction that forms H₂ gas bubbles?

c. Why is it preferred to use sodium borohydride over other reducing agents?

Figure 8.3 Synthesis, Isolation, and Distillation of 2: (+)-3-(dimethylamino)-1-phenylpropanol From 3- dimethylaminopropiophenone hydrochloride CH 2. Na0H 4. NaBH, - || H 1. soluble in water "free base" insoluble in water 3. add EtOH OH تو 5. HCI CI- N 6. NaOH H "free base" 7. extract with ether

Answer 1

a) Protonated form of N is acidic and if NaBH4 is used it acts as base removing H+ from protonated N. Hence we wont get reduction reaction. Hence base is used initially to remove H+ from protonated N. Then we can use NaBH4 to reduce C=O.

b) Step 3  , where HCl is used produces H2 ,

c) NaBH4 is mild reducing agent and reduces Carbonyl to C-O-. Other reducing agents react vigorously and can be explosive. Hence NaBH4 is preferred