The first azo dye was made by reacting aniline (phenylamine) with potassium dichromate.

 

Anyone knows the mechanism or the products?

 

Thank you very much!

The product is called mauve: (sulfate counter-ion not pictured)

 

But it turns out Perkins didn't have pure anniline at his disposal. He probably had a mixture of o-,m-,and p- toluidines as is evident from the structure of mauve.

Actually this reaction doesn't proceed by the traditional diazonium coupling route. Usually this transformation is accompliched by reacting nitrous acid and sodium chloride with an amino-substituted aromatic. This produces a very heat sensitive diazonium/chloride salt. The positivley charged nitrogen in the azo moiety then acts as an electrophile, attacking a [math] \pi [/math] dense region of another aromatic ring to form an Ar-N=N-Ar linkage. I've done similar reactions before, they are hard to control and vary hard to keep from "gelling" up in the middle of the reaction. However the products are beautiful and can very easily be identified with UV/vis.

Edited November 6, 201015 yr by mississippichem

That's not an azo dye.

Sorry guys, it is not an azo dye; it is the first aniline dye.

Sorry guys, it is not an azo dye; it is the first aniline dye.

 

Yeah not an azo dye. No (R-N=N-R), forgot to mention that. Not formed by a diazonium coupling either. But the OP wanted the mechanism and products from the reaction of anniline and potassium dichromate. I Found this listed on a timetable of azo-dye technologies. I thought the original poster might be lumping this is with the "real" azodyes.

 

-Is there even a route to diazonium salts from anniline without using a source of [ce] NO_{2}^- [/ce]?

Edited November 7, 201015 yr by mississippichem

The oxidation of some alkylhydrazines gives diazonium compounds.

I'm not sure if these alkylhydrazines can be made from hydrazine and, for example, a halogenated arene.

It's possible that the only ones that you can make this way (like dinitrophenylhydrazine) don't oxidise to diazonium compounds.

The oxidation of some alkylhydrazines gives diazonium compounds.

I'm not sure if these alkylhydrazines can be made from hydrazine and, for example, a halogenated arene.

It's possible that the only ones that you can make this way (like dinitrophenylhydrazine) don't oxidise to diazonium compounds.

 

 

"Activated" dimethyl sulfoxide efficiently dehydrogenates hydrazones to the respective diazo compounds at -78°C. Under optimized conditions, simple vacuum filtration provides solutions of pure diazo compounds from which stable diazo species can be isolated in high yield, or that can be directly used in subsequent reactions.

M. I. Javed, M. Brewer, Org. Lett., 2007, 9, 1789-1792.

 

Wonder if this can be done with an alkyl hydrazone?