nuchem - 30-7-2015 at 11:35
I recently got a hold of some indigo dye and I want to turn it into indigo carmine for the Chemical Stop Light experiment.
Do I simply have to sulfinate the indigo, then neutralize it with NaOH? Or is the process a little more complicated than I think?
C16H10N2O2 + 2H2SO4 =
C16H10N2O8S2 + 2H2O
C16H10N2O8S2 + 2NaOH =
C16H8N2Na2O8S2 + 2H2O
Indigo Carmine
nuchem - 5-8-2015 at 12:34
Recently I made a post about Indigo Carmine, and well, I got no bites on it. My guess is because I had it in the wrong category, so now here is my
attempt with you organic chemist.
I am trying to synthesis Indigo Carmine, I found some references online to help me get going, but none of them were complete. For example, one source
told me how to synthesis "Indigo carmine" but the process itself told me how to make Indigotindisulfonate, which is
C16H10N2O8S2... Not the Carmine, which is
C16H8N2Na2O8S2
Essentially my question is: does anyone know a solid method of producing Indigo Carmine? If so, can you please post your process?
Aqua-regia - 6-8-2015 at 03:27
Do you have indigo?
MrHomeScientist - 6-8-2015 at 05:28
Googling "indigo carmine synthesis" yields a few useful results. It seems you just add indigo to concentrated sulfuric acid, heat for a while, then
dilute with water to precipitate unreacted indigo. Then presumably you neutralize the solution and let it evaporate to crystallize the carmine. I'm
not very experienced with organic chemistry, though. Try it and report back!
The chemical traffic light is a great demonstration. I use it all the time in my educational outreach programs. I discovered that, if you want to let
kids shake the flask, indigo carmine is very quickly exhausted. My tests gave out at about 12 careful shakes, but I had one kid destroy the dye with
one mighty shake. He was the first one that walked up to the table 
The blue
bottle is much better for energetic kids - that dye lasts through anything!
nuchem - 6-8-2015 at 05:37
@Aqua-regia
Yeah, I got quite a bit of it actually.
@MrHomeScientist
I will give it my best effort and report back to ya!
Aqua-regia - 6-8-2015 at 07:33
OK dissolve 2,5 g indigo with 30 ml 96% sulfuric acid and mix in 90 C degrees for half hours. Pour it in 150 ml cold water, and filter. Add to the
filtered solution 30 g NaCl and mix again, till the salt complet dissolve.
Put the solution in the fridge for few hours, your indigocarmine will cristallize out. Filter off, wash with conc NaCl solution and dry it. Thats all.
Indigo can sulfonate in mild condition , dont need oleum.
[Edited on 6-8-2015 by Aqua-regia]
[Edited on 6-8-2015 by Aqua-regia]
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nuchem - 6-8-2015 at 10:51
Thanks Aqua!!