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Question

what would be the correct sequence for the preparation of 3-Propynamine via Gabriel synthesis: 

1. K2CO3 abstracts a proton to give a nucleophile
2. Phthalic acid reacts with ammonia to give phthalimide
3. Reaction of Nuleophile with 3-bromopropyne
4. Hydrolysis
  1. 2; 1; 3; 4
  2. 1; 3; 4; 2
  3. 1; 2; 3; 4
  4. 2; 1; 4; 3


Solution

The correct option is A 2; 1; 3; 4
Usually, the synthesis starts with phthalic acid, which is converted into phthalimide:

In the next step, using a base, the acidic hydrogen attached to the nitrogen of the imide is abstracted to yield an anion (which remains as part of a salt); this anion is a capable nucleophile:

The above salt (potassium salt of phthalimide), when treated with 3-bromopropyne, gives the following product via an SN2:

Once we get to the above product, hydrolysis will give the required 3-propynamine:

The hydrolysis could be done in different ways (using an acid or a base). Treatment with hydrazine is a convenient method.

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