fermium
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Please help me get rid of aniline dyes
Hello,
My mad-scientist task is to remove the color of two aniline dyes, mauveine and basic fuschin:
structure of mauveine:
http://en.wikipedia.org/wiki/Mauveine
structure of basic fuschin:
http://www.nilechemicals.com/basic.htm
The best and easiest way to do this is simply by washing out the dyes in a solvent in which both are soluble. For example both are soluble in water
and in alcohols.
However in my experience this process is too time-consuming so I am looking for a more effective solvent.
Also, after washing there is still sometimes a faint residual color which is very difficult to remove. I want to be able to bleach out the color of
the residual dye. Oxidative bleaching with H2O2 and reductive bleaching with NaBH4 were somewhat but not entirely effective.
So the essence of my question is
(A) what are these theoretically most soluble in? Since they are aromatics and they are derived from aniline, would aniline itself be a good solvent?
Can you think of other likely possibilities ?
(B) is there a reaction which will decolor these dyes by wrecking the chain of conjugated double bonds, either by cleavage or by forming an
irreversible adduct
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Marvin
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I would be inclined to try dilute acid. Compounds with -NH3 tend to be bases and soluable in acid.
I would also be interested to know what would happen if you diazotised and then boiled the cloth. That might affect the colour, it should render it
soluable in base and it might make it easier to destructivly oxidise.
How drastic you can be depends on the dyed material.
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garage chemist
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Did you actually use NaBH4 for bleaching?
I always thought it was MUCH too expensive for this application.
To answer your question: sodium hypochlorite is a great bleaching agent. It destroys most organic molecules. Try it out, but don't use too
concentrated solutions, otherwise it might attack the cloth.
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fermium
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Aniline dyes redux
Hello, thanks for the replies!
Marvin: I have tried muriatic acid + water to give HCl about 10% and it is more effective than straight water on the fuschia.
I was wondering if you could elaborate on an actual procedure for diazotization (I would have to prepare nitrous acid from nitrite?) To me this seems
like a very good idea because it would exploit a characteristic property of the molecules .
Also let's say hypothetically that aqueous solution is not an option for washing, if you have to move up the chain of [probably increasingly
nasty] organic solvents what would you choose?
________________________________
Garage-chemist: Yes I did use NaBH4, costs about $1/gram, seems to work better on the mauve than on the fucshia.
Why? Dunno, I am thinking about the actual mechanism of the reductive bleaching but thus far don't have a good answer. Other than the fact that
mauveine has a more complex structure so there's more stuff in it to be wrecked  .
Hypochlorite has also been tried and seems to be a big no-no because it is way too destructive towards the substrate, can make whitish cloth
for sure but at the micro level eats away at the fibers and burns it full of holes.
_________________________________
Anyone else out there have an opinion on diazotization or on an organic solvent for these ?
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JohnWW
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Aqueous hypochlorite works by adding across double bonds (or after decomposing to Cl2 gas and hydroxide), thereby destroying the systems of several
conjugated double bonds, often including azo groups, which are usually responsible for the light absorption and hence colors of dyestuffs. It depends
on the composition of the fiber substrate as to its effects on the fibers.
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Mendeleev
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I would try solid Ca(ClO)2, this stuff turned cardboard white. I can't believe you actually wasted sodium borohydride on bleaching  . If only I could have some.
Trogdor was a man. A dragon man. Or maybe just a dragon. . .
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