Azo-Dyes

What is there to say on this self contained little topic.

If you have a benzene interconversion map you should have it all on there.

Here is a little summary of the topic just to make sure you know what is going on.

I am not going to go through the pathway from benzene to benzenediazonium chloride.. .oh, OK then I will

1. Benzene with Conc H2SO4 and Conc HNO3 (at about 50C) makes Nitrobenzene
2. Nitrobenzene with Tin and Conc HCl makes Phenylamine
3. Phenylamine with Sodium Nitrite and Conc HCl - Nitrous Acid (below 5C) makes Benzenediazonium chloride

Happy now?

This is benzenediazonium chloride

Benzenediazonium chloride and nitrous acid are unstable above 5C so you have to keep it cool when this stuff is around.

If you let things get a bit hot you get phenol and some bubbles of nitrogen gas given off (that sounds like a test to me).

Benzenediazonium chloride can be added to loads of molecules with benzene rings to make dyes. The three examples you need to know are with...

1. Phenol

2. Napthalen-2-ol

3. Phenylamine

Pretty repetitive really.

The only relatively interesting thing to point out her is why the O- on napthalen-2-ol and phenol (as opposed to -OH. This is explained by the condition needed which is in NaOH (i.e. alkaline conditions). All acids lose their proton in alkaline conditions and as both of these phenolic groups are alkaline then  - protons begone!

These two benzene rings linked by a N=N are a chromophore so all of these molecules are dyes. 

You don't need to be able to name them as they have several possible names, just remember the formula.

OK, enough chemistry for me for one evening it's back to the mince pies and TV.