These questions are based on the Synthesis of Methyl Orange lab using p-Sulfobenzeneazo-4-dimethylaniline sodium salt. 1....

These questions are based on the Synthesis of Methyl Orange lab using p-Sulfobenzeneazo-4-dimethylaniline sodium salt.

1. What is the need of adding NaOH during coupling reaction (here)? Write necessary equation.

2. Based on pKa of MO (3 4), what will be the color of MO in regular water?

3. Identify active electrophile(s) and nucleophile(s) during coupling reaction with necessary structures.

Expert Solution

1. The Azo salt (i.e. p-Sulfobenzeneazo-4-dimethylaniline sodium salt) is prepared by Sulfanilic Acid and N,N-dimethylaniline.Now, in order to dissolve an acid to react,(i.e. Sulfanilic Acid) from our preliminary knowledge of Acid-Base chemistry,we know that, a base is required.Here NaOH serves that purpose.The reaction is given below-

2. The Methyl Orange acts as an acid base indicator by changing its colour in Acidic and basic solution based on its pKa value as standard(here the standard of acidity and basicity is considered w.r.t M.O.which has pKa=3.4). Hence in water which has pH=7 (basic soln w.r.t MO) at 25 degree C, the colour of Methyl Orange is Yellow.

3.The complete reaction is outlined below with mechanism,the first step being to dissolve Sulfanilic acid in NaOH followed by-

Nitrosonium ion formation from NaNO2-

Here acts as a Nucleophile.

Formation of p-Sulfobenzeneazo-4-dimethylaniline sodium salt-

where the nucleophilic attacks are mentioned in the mechanism.

queen_honey_blossom answered 2 years ago

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