Priest
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Change of color at Henry-cond. caused by...?
Hi!
So as this is my first post in this forum, and, as I realized after few minutes, definitely not the last one, I wanted to be polite and introduce me
just within a few words;
Im 24 years old, live in Germany where I study Biotechnology. About three years before I started getting into chemistry by myself, and it has become
one o the center points in my life until today as the hobby became business...
one other is mixing&little producing NeuroFunk/Drum&Bass...
to come back to my question:
I had problems the last days as I tried to oxidise substituted Benzylalkenes with KMnO4 (what was expectable because I could not affort PTC, not even
THF) and yielded the over-oxidized carboxylic acid instead of the aldehyde. I originally wanted to perform the alkalimetal-base catalyzed
Nitroaldole-addition of Nitromethane on a substituted Benzaldehyde, and somewhere (cant remember...) I read about the possibility that one can also
apply the Henry- condensation on some specific carboxylic acids, by forming the same reaction mechanism as the regular rxn is after, a first
deprotonation of Nitroalkane to the Nitroalcoholate, which increases the electrophilic character on the alpha-C, which induces its nucleophilic attack
on the Carboxyl-C.
So I proceeded as usual with only a small batch as I already expected no / low yields. At the point where the Acid was added to protonate the C-OH for
the leaving H2O I even havent been much excited, because I was pretty sure that it could not be so simle to manufacture carboxylic acids. But then,
the same process of first changing completely blue and then shifting over green to somewhat yellow, appeared in the reaction-solution made out of
carb.acid. I was pretty surprised by that and I'm asking further:
Where does this change of color come from?
By which mechanism is it produced?
Could the optical sign of colors changing perhaps be understood as an indicator for eg the nucleophilic attac or complex-formation?
Thats all for it now, I hope somebody can tell me...
Take care of yourselfs and those around you, Priest
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vulture
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Your experiment description is a bit confusing. You mixed benzoic acid and nitromethane and acidified, right?
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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stoichiometric_steve
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the blue-green-yellow fade is characteristic for nitroalkenes when treated with mineral acid. most likely, a dimeric adduct occurs as an intermediate.
i think you didnt want to make a carboxylic acid instead of a nitroalkene.
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Priest
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| Quote: | Ursprünglich verfasst von vulture
Your experiment description is a bit confusing. You mixed benzoic acid and nitromethane and acidified, right? |
after mixing and cooling I added the base over about 20 min at < 10 C and acidified, yes.
| Quote: | Ursprünglich verfasst von stoichiometric_steve
the blue-green-yellow fade is characteristic for nitroalkenes when treated with mineral acid. most likely, a dimeric adduct occurs as an intermediate.
i think you didnt want to make a carboxylic acid instead of a nitroalkene. |
ehm, I went out from the carboxylic acid and added the nitroalkene...
Are the properties of the carboxyl-C between the acid and the aldehyde so different for nucleophilic addition?
but thanks for the answers so far...
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stoichiometric_steve
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| Quote: | Originally posted by Priest
ehm, I went out from the carboxylic acid and added the nitroalkene...
Are the properties of the carboxyl-C between the acid and the aldehyde so different for nucleophilic addition?
but thanks for the answers so far... |
actually, since you added base, you don't have a carbonyl oxygen anymore, instead you end up with a resonance stabilized carboxylate, which is not
very reactive. i doubt you made anything important here. perform a TLC or other identification. anything else here is speculation.
and i think you meant to say that you added nitroalkAne, not alkEne.
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Priest
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oh sorry! Of course I meant nitroalkane...
ok thanks, that explains why it couldn't work. I thought that the fade of color perhaps could be a sign for the alkylation mechanism but you already
said it has to do with the dimer... in more detail its the protonation of the dimer isn't it? does the change come from a resonance stabilization
process in which the molecule runs through several wave spectres?
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Nicodem
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Welcome to the forum.
I really have no clue how to answer your questions since I have no idea what you did, but I could help you with an advice. When you ask questions of
the type "what happened in my experiment…?" make sure to describe what the hell you are talking about. I'm quite sure nobody reading your post is a
telepath able to read your mind, so the first thing you need to do is describe the experiment. The other thing to do is to skip the nonsense and write
down only the relevant information. From your post it is clear that you know almost nothing about reaction mechanisms so it makes no sense to write
down your confusions. Believe me, reading other's confusions can be really confusing.
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