Question

Both m-bromoanisole on reaction with sodamine and liquied ammonia

Answer 1

explanation:

These are the reaction conditions for generating benzyne intermediates.

The reaction of ortho-bromoanisole with potassium amide in liquid ammonia (b. p. -33 °C) is extremely rapid.

Step 1. The amide ion attacks the  

H

atom that is ortho to  

C3

, generating a carbanion.

Step 1

Step 1

Step 2. Loss of  

Br

-

to form a benzyne intermediate.

Step 2

Step 2

The elimination is by an E2cb pathway.

Step 3. Addition of  

NH

-

2

The strain caused by a triple bond in a benzene ring can be relieved by a nucleophilic addition (

Ad

N

) of  

NH

-

2

.

The methoxy group is electron-withdrawing by induction, so the nucleophile will attack  

C3

to place the carbanion as close as possible to the methoxy group.

Step 3

Step 3

Step 4. Protonation of the carbanion.

Step 4

Step 4

The product is meta-methoxyaniline.

para-Bromoanisole

The reaction with para-bromoanisole also follows a benzyne mechanism.

Step 5

Step 5

The nucleophile can attack either end of the triple bond, and the methoxy group is far enough away that its inductive effects are minimal.

Step 6

Step 6

The product is a mixture of para- and meta-methoxyaniline.

Related questions

Why is the product of the addition of  

C

l

2

to trans-2-butene a meso compound?

xplanation:

These are the reaction conditions for generating benzyne intermediates.

The reaction of ortho-bromoanisole with potassium amide in liquid ammonia (b. p. -33 °C) is extremely rapid.

Step 1. The amide ion attacks the  

H

atom that is ortho to  

C3

, generating a carbanion.

Step 1

Step 1

Step 2. Loss of  

Br

-

to form a benzyne intermediate.

Step 2

Step 2

The elimination is by an E2cb pathway.

Step 3. Addition of  

NH

-

2

The strain caused by a triple bond in a benzene ring can be relieved by a nucleophilic addition (

Ad

N

) of  

NH

-

2

.

The methoxy group is electron-withdrawing by induction, so the nucleophile will attack  

C3

to place the carbanion as close as possible to the methoxy group.

Step 3

Step 3

Step 4. Protonation of the carbanion.

Step 4

Step 4

The product is meta-methoxyaniline.

para-Bromoanisole

The reaction with para-bromoanisole also follows a benzyne mechanism.

Step 5

Step 5

The nucleophile can attack either end of the triple bond, and the methoxy group is far enough away that its inductive effects are minimal.

Step 6

Step 6

The product is a mixture of para- and meta-methoxyaniline.

Related questions

Why is the product of the addition of  

C

l

2

to trans-2-butene a meso compound?