Keras
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Registered: 20-8-2018
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Synthesising thymol blue
Folks,
I’m currently happy trying to home-make a collection of pH indicators and dyes, and I chanced on thymol blue (which can then be brominated into
bromothymol blue). It doesn’t seem that difficult to make, except for the o-sulphobenzoic anhydride.
Apparently, the ammonia salt of o-sulphobenzoic acid is obtained easily by acid hydrolysis of the acid form of saccharin. But then the next step to
o-sulphobenzoic anhydride involves thionyl chloride, which I don’t have. Question is: is anyone aware of an alternative route from the
o-sulphobenzoic salt to the anhydride using something else? Concentrated sulphuric acid?
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Niklas
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Simply trying to sublime the sulphobenzoic acid like you would for making phthalic anhydride may be worth a shot, alternatively heating with H2SO4 or
P2O5 or something of the kind seems reasonable.
Both methods are mentioned in the discussion section if the Orgsyn article for sulfobenzoic anhydride (http://www.orgsyn.org/demo.aspx?prep=CV1P0495), so I see quite a good likelihood of it working.
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Keras
International Hazard
Posts: 1143
Registered: 20-8-2018
Location: (48, 2)
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Yeah, I’ll give it a shot when I get to it. I still have several projects on my backlog, but I’ll keep you posted if you want.
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Boffis
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Hi Keras, have you seen this SM thread:-
http://www.sciencemadness.org/talk/viewthread.php?tid=158116...
Check out the paper linked to the second last post. Basically it is the preparation of sulphophthalein dyes direct from saccharin and a phenol.
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