Question

19) Give following conversions by using acetaldehyde
as starting material.
(a) Lactic acid and acrylic acid
(b) Alanine
(c) 1-amino propane-2-ol
20) Give the structuren​

Answer 1

Conversion of acetaldehyde into the following -

a) Lactic acid and Acrylic acid-

Here ,we use HCN where CN- acts as nucleophile and attack on the carbonyl carbon as it carry partial positive charge . Cyanohydrin will form whose hydrolysis will give the lactic acid which on dehydration gives acrylic acid.

OH

|

CH3-CHO + HCN → CH3- CH- CN

Acetaldehyde cyanohydrin

↓H3O+

OH

|

-H2O CH3-CH-COOH CH2=CH-COOH ← Lactic acid

acrylic acid

b) Alanine -

• Acetaldehyde on reaction with NH3 and HCN gives alpha - amino propionitrile which on hydrolysis gives Alanine.

NH2

| CH3-CHO +NH3 + HCN → CH3- CH- CN

Acetaldehyde alpha-amino propionitrile

↓H3O+

NH2

|

CH3-C-H

|

(Alanine) COOH

c)1-amino propane-2-ol -

• Acetaldehyde react with HCN to give cyanohydrin where CN- acts as nucleophile and attack on carbonyl carbon so we get cyanohydrin . In Cyanohydrin , nitrile group on partial hydrolysis gives amide which on reacting with reducing agent LiAlH4 in the presence of dry ether and H20 gives 1-amino propane-2-ol.

OH

|

CH3-CHO + HCN → CH3- CH- CN

Acetaldehyde cyanohydrin

(partial hydrolysis) ↓H20

OH OH

| LiAlH4 |

CH3- CH-CH2-NH2 ← CH3-CH-CONH2 1-amino propane-2-ol dry ether

H2O