Question

3.
alco.
Na/ethanol
i Identify A and B in the following reactions.
C6H5CH2Br
A
B.
KCN​

Answer 1

Answer:

CH

3

−CH

2

−Br+AgCN

Δ

−AgBr

A, ethyl isocyanide

CH

3

−CH

2

−NC

→

C

2

H

5

OH

Na

B, ethyl methyl amine

CH

3

−CH

2

−NH

2

−CH

3

Ethyl bromide reacts with silver cyanide to form ethyl isocyanide.

Na/ethanol reduces ethyl isocyanide to ethyl methyl amine.

Hoffmann bromamide degradation reaction:

Treatment of amide with bromine and aqueous ( or alcoholic) NaOH, a primary amine is obtained.

CH

3

−CONH

2

+Br

2

+4NaOH→CH

3

−NH

2

+Na

2

CO

3

+2NaBr+2H

2

O

The product amine has one C atom less than starting material amide.

Answer 2

Answer:

Question:-

Identified A and B in the following reactions.

$C_{6} H_{5} CH_{2} Br$ + $\frac{Alcohol}{KCN}$ ⇒  $A$ + $\frac{ Na}{Ethanol}$ ⇒ $B$.

Answer:-

In the above reaction, $A$ & $B$ are the following compounds formed:-

$A$ ⇒ $C_{6} H_{5} CH_{2} CN$ (Benzyl cyanide)

$B$ ⇒ $C_{6} H_{5} CH_{2} CH_{2} NH_{2}$ (Phenylethanamine)

Explanation:

$C_{6} H_{5} CH_{2} Br$ + $\frac{Alcohol}{KCN}$  ⇒  $C_{6} H_{5} CH_{2} CN$ + $\frac{ Na}{Ethanol}$ ⇒ $C_{6} H_{5} CH_{2} CH_{2} NH_{2}$.

• In the first part of the reaction, haloalkane $(C_{6} H_{5} CH_{2} Br)$ reacts with  $alc. KCN$ to form alkyl cyanide $(C_{6} H_{5} CH_{2} CN)$ as the main product.
• The cyanide ion is an ambident nucleophile. Most alkali metal cyanides, including NaCN and KCN, are ionic.
• The reaction might theoretically take place through either nitrogen or carbon.
• However, in reality, the reaction takes place through carbon because C-C bonds are stronger than C-N bonds, and as a result, the main products are alkyl cyanides.

• In the second part of the reaction, alkyl cyanide $(C_{6} H_{5} CH_{2} CN)$ when reacted to sodium and ethanol gets reduced to give primary amines $(C_{6} H_{5} CH_{2} CH_{2} NH_{2})$.
• In this reaction, the nitrile group is hydrogenated in this process to create a primary amine.
• This is a helpful way to lengthen a carbon chain when making a primary amine that has one extra carbon atom than the alkyl halide used to make alkyl cyanide.

#SPJ3