Synthesis of the Diazonium Salt of 4-Nitroaniline

The synthesis of azo dyes is accomplished in two steps:

In the first step, an aromatic amine (aniline) is transformed into a diazonium salt by the reaction of nitrous acid (HNO2) obtained in situ by mixing sodium nitrite and a mineral acid

Diazotization reactions are usually performed at low temperatures to avoid the decomposition of the diazonium salts...these compounds are unstable at higher temperatures due to their tendency to expel nitrogen gas – some diazonium salts are explosive when dry and must be kept in solution

Diazotization of 4-Nitroaniline

Step 1. Prepare reagents

"Substrate" test tube

substrate.mp4

0.35 g of 4-nitroaniline, 0.19 g of sodium nitrite, and 0.75 mL of water

"Acid" test tube

acid.mp4

0.75 mL water and 0.75 mL conc. HCl*

(*SAFETY: important to add water first, then acid)

Step 2. Synthesis of the diazonium salt

synthesis_diazosalt.mp4

Cool both test tubes in an ice-water bath
Slowly transfer the acid solution drop-wise to the substrate solution, stir gently with a glass rod in between drops
After the addition, stir occasionally for 10 minutes

Step 3. Isolate the diazonium salt

isolate_diazosalt.mp4

Add a few ice cubes to a separate test tube
Loosely pack a small piece of cold, wet cotton into a glass funnel
Filter the reaction mixture and collect the filtrate in the test tube with ice
Rinse the substrate test tube with 2 mL of cold water

NEXT: coupling reactions with the diazonium salt! (Part B)

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