Advices For Studying Organic Chemistry

C

O OH

H 2 O

87%

no anol

H 2 CH 3 C CH 3 H 3 CH 2 C CHCH 3

NaBH 4

2-Buta ne 2-But

5. The key step in the reduction of a carbonyl compound by either LiAlH 4 or NaBH 4

1)

Mechanism for the Reaction

is the transfer of a hydride ion from the metal to the carbonyl carbon.

The hydride ion acts as a nucleophile.

A

Reduction of Aldehydes and Ketones by Hydride Transfer

BH 3 H H OH

R

R'

C

O

δ+ δ−

+

R'

H C O −

R

R'

H C O H

Hydride transfer Alkoxide ion Alcohol

R

(^)

6. NaBH 4 is a less powerful reducing agent than LiAlH 4.
   
   
   1. LiAlH 4 reduces acids, esters, aldehydes, and ketones.
   
   
   2. NaBH 4 reduces only aldehydes and ketones.
   
   
   
   

C O− C C C

O

R OR'

O

R H

O

<<R' R

O

R <

ReducedbyLiAlH 4

Ease of reduction

ed by NaBH 4

7. LiAlH 4 reacts violently with water reductions with LiAlH 4 must be carried

1) over to decompose excess

Recuc

⇒

out in anhydrous solutions, usually in anhydrous ether.

Ethyl acetate is added cautiously after the reaction is

LiAlH 4 , then water is added to decompose the aluminum complex.