Sciencemadness Discussion Board

6-nitro,2-amino-phenol-4-sulfonic acid Dye Intermediate

pawan - 14-6-2009 at 03:03

As suggested in - Dyes classified by intermediates, to get this compund -

1. Sulphonation of phenol.
2. Di nitration of p-sulfonic phenol.
3. Partial reduction to get 6-nitro,2-amino-phenol-4-sulfonic acid.

I carried out phenol sulfonation at 100°C to get para sulfonic phenol. It is fine till now.

But I am confused on dinitration of this product as literature says it may even convert / replace HSO3 group also into nitro group and may result in picric acid. Is it possible to do it at some very low temperature in some solvent e.g. CS2 etc.

Or should I synthesize it from 2,6-dintrochlorobenzene-4-sulfonic acid which is easier to prepare and then replace Cl by the hydrolysis in to phenol as already mentioned in this forum and on Org Synth also.?? In this case, I am not sure about stability of sulfo group as it requires strong alkali presence to convert chloro group to phenol group.

Any help is welcome.

not_important - 14-6-2009 at 22:52

With 2 ortho nitros and a para sulphonic, the chlorine should come off fairly readily, boiling in aqueous alkali should do it.

Or you could mononitrate, reduce to the aniline, acetylate, and mononitrate again. The AcHN- is activating o,p but I think would lose out to the strongly activation o,p of the -OH and the m directing -SO3H which would also contribute a little crowding at the 5 position ortho to it.

pawan - 15-6-2009 at 02:55

Thanks for your response.
Quote:

Or you could mononitrate, reduce to the aniline, acetylate, and mononitrate again. The AcHN- is activating o,p but I think would lose out to the strongly activation o,p of the -OH and the m directing -SO3H which would also contribute a little crowding at the 5 position ortho to it.


Starting material is phenol or chlorobenzene in this case. Also, acetylation of amino group to get AcHN to keep -NH2 protected or something else.

Can you please make it more clear.

not_important - 15-6-2009 at 04:11

phenol => 4-sulpho-phemol =(> 2-nitro-4-sulpho-phenol =(reduction)=> 2-amino-4-sulpho-phenol => 2-acetamino-4-sulpho-phenol => 2-acetamino-4-sulpho-6-nitro-phenol.

pawan - 15-6-2009 at 22:17

Thanks for details
Can I get any reference for mono nitration of 4-sulfo phenol?
This is where I am failing to get a good reference for operating conditions.

Sauron - 15-6-2009 at 23:14

The references are likely in Ullmann's as well as in "Fundamental Processes of Dye Chemistry" in forum library. You really ought to search them out yourself, you can't expect constant spoonfeeding. This is basoc stuff and rather boring.

Phenol-4-sulfonic acid ought to dinitrate readily and getting it to do so without the sulfonic group falling off is a matter of reaction conditions. The half reduction is a classocal pone with ammonium sulfide (NH4OH and H2S).