[darkdevil]

Greetings,

I wonder if there are any known methods to oxidize indigo to its oxidized form "dehydro-indigo" (structure is attached below) without using the electrochemical method?
Is it possible to oxidize the poorly soluble indigo (due to strong intermolecular hydrogen bonds) with some common oxidizing agents in lab?



Thank you so much!

[opsomath]

Well, it's soluble in nitrobenzene and chloroform, as well as sulfuric acid:

http://en.wikipedia.org/wiki/Indigo_dye

In acid, perhaps hydrogen peroxide could be used, or something like persulfate. Probably the difficulty is avoiding overoxidation into what is called "brown crap."

I found one source which mentioned that it could be oxidized by "mild oxidizing agents" with a citation I had difficulty following, but which mentioned the use of PbO2, MnO2, KMnO4, and oxygen with palladium black.

http://books.google.com/books?id=1K-2AAAAIAAJ&lpg=PA1245&ots=08p8YCjtHJ&dq=oxidation%20of%20indigo%20to%20dehydroindigo&pg=PA1245#v=onepage&q=oxidation%20of%20indigo%20to%20dehydroindigo&f=false

Please note that if you don't know what you're doing, any of these reagents could easily hurt or kill you.

[Dan]

Kalb, L. Chem. Ber., 1909, 42, 3642–3652. Link.

[darkdevil]

Thank you very much for the replies

FOr chloroform, I dont think indigo is quite soluble in it. I cannot see anything in the proton NMR of indigo using d-chloroform. The spectrum is just blank even I increased the concentration/temperature or ultrasonicated the sample.

And indigo sulfate will be produced if sulfuric acid is used..


What I am trying to do is to make indigo soluble in organic solvents for any of its modification..