madscientist
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Organic substitutions
It is possible to carry out organic substitutions with considerable ease when using an electric current. I believe this is because any anions that are
electrolyzed become neutral radicals / atoms. Fluorinations occur very easily. Fluorination of organic compounds will proceed until all hydrogen atoms
have been replaced with fluorine atoms. For example, trifluoroacetic acid can be prepared by electrolyzing a solution of hydrofluoric acid and acetic
acid.
6[H+] + 6[F-] + 6e ----> 6H + 6[F-]
The fluorine anion then loses its extra electron at the anode...
[F-] ----> F
...Thus becoming a free atom.
[CH3COO-] + [H+] + e ----> H + [CH3COO-]
The acetate anion then gives up its charge at the anode...
[CH3COO-] ----> CH3COO
The flourine atoms react easily with the CH3COO radical.
CH3COO + 7F ----> CF3COOF + 3HF
CF3COOF hydrolyzes:
CF3COOF + H2O ----> CF3COOH + HOF
There is a lot that can be done in the field of organic substitutions using electric current - the above example is just one among many. Anyone have
something interesting to share on this topic?
I weep at the sight of flaming acetic anhydride.
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vulture
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Which electrode on earth could be resistant to HF?
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Polverone
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Platinum and carbon at least. Graphite electrodes are messy but they're the best friend of an amateur electrochemist who can't afford platinum. I'm
wondering if this would work with hydrochloric acid to form trichloroacetic acid. I think I will find out soon...
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Rhadon
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Did you try it yet  ? I'm interested in this procedure, and if it works I'll also
make trichloroacetic acid that way.
If trichloroacetic acid isn't possible, being able to synthesize monochloroacetic acid without having to bother with P / Cl2 would also be an
achievement.
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Polverone
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No...
I haven't gotten around to it yet. I found a project that has been keeping me busy in all spare hours, and soon I leave for a weeklong conference. But
I think you will like my project when you see it.
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PrimoPyro
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Got a Ref?
To the poster of the first post:
Do you have a ref or anything for that reaction of fluorine and acetyl radicals?
Are you aware that carboxyl radicals decompose almost instantaneously to yield RCOO[radical] --> R(radical) + CO2.
The normal reaction then produces 2R --> RR where the R radicals pair up.
This is often referred to as the Kolbe Process, and is useful for preparing alkanes from carboxylic acids. Mixed Kolbe reactions are known, and the
product is one of three possibilities:
R + L --> RR + LL + RL
The ratios of each product can be influenced somewhat by using more of one reagent compared to the other.
PrimoPyro
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madscientist
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I found those reactions in my inorganic chemistry textbook.
I weep at the sight of flaming acetic anhydride.
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Voltforce
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Hi- this is just my second post.
Did anyone here hear about borodiamonds? They are supposed to be a little bit more conductive than graphite and much more durable. I have not seen
them marketed anywhere so if anyone knows of anywhere I could find some, I would appreciate it.
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vulture
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Are you referring to boroncarbide, an extremely durable and chemically resistant compound?
One shouldn't accept or resort to the mutilation of science to appease the mentally impaired.
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Organikum
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trifluoroacetic acid
Wow! I have been searching a way for TFAA synthesis the last week and got nothing. Espacenet brought nothing usefull up and nobody else had a clue.
Thanks.
Does your textbook tell more on cell construction, ampere per cm2 needed, current electrolyte used, cathode and anode material? Single chamber cell or
two or more chambers, if more what membranes or salt bridges are used? Temperatures and time?
ok, ok, the name of the book or if references on this are named the references and I will look it up. No need for spoonfeeding....
I am after this for some time and this is the first time I see a chance.
thanks
ORGY
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Polverone
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patent fun
browsing www.uspto.gov with appropriate keywords and a TIFF viewer installed yielded some goodies:
US patent 3,576,860 has a method for preparing monochloroacetic acid in high yield with very little higher-chlorinated acid as impurity (interesting
to me if not to you). Methyl chloroacetate is made from monochloroacetic acid and can be used with KF to form methyl fluoroacetate, which can be used
to prepare fluoroacetic salts and the free acid. I wonder if you could do the same with trichloroacetic acid: form its methyl ester and and react it
with KF in an autoclave for a few hours to form the fluorinated ester? Then form the salt and regenerate/distill off the acid... Even if it would
work, it seems like an awful lot of effort.
US patent 2,717,871 explains how to fluorinate various things using electricity and HF. You can apparently start with monochloracetic acid and
fluorinate it to trifluoroacetyl fluoride, which can be hydrolyzed to give trifluoroacetic acid. It might even be worth starting with glacial acetic
acid instead of some haloacetic compound. The process really, really doesn't strike me as something that is suitable for improvised implementation,
but I doubt that there are any easy and safe routes to trifluoroacetic acid, unless you can get some more potent fluorinating agents.
I have a couple of volumes about fluorine chemistry at home. I'll see if there's anything in them about trifluoroacetic acid later.
Can you buy HF, or is that something that you will have to make yourself? All of these compounds are very nasty and I hope that you have thorough
safety precautions in place.
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Polverone
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jackpot!
I think that you are really going to like this:
Preparation of Trifluoroacetic Acid
DONALD RAE ALLEN;
J. Org. Chem.; 1961; 26(3); 923-925.
I will not be able to download the full article until January, when my school begins receiving access to the ACS archives, but I was able to view the
first page. And it looks great! It uses air, water vapor, 1,1,1-trifluoroethane, and a high-voltage discharge to produce trifluoroacetic acid without
side reactions.
What's really nifty about it? First, the authors used homemade apparatus that a home experimenter could duplicate (Pyrex tubing, aluminum foil, and a
neon sign transformer). Second, 1,1,1-trifluoroethane is also known as Freon 143a. It's a non-ozone-destroying refrigerant. It is produced on an
industrial scale and is not at all suspicious. I haven't yet seen price quotes, but I have already seen several online establishments that claim to
sell it. I would imagine that you would be able to find a source for it without going online if you can find a local place that handles refrigeration
or air conditioning equipment. It seems to be called RFC-143a as well as Freon 143a.
You don't need to handle fluorine, HF, or any other nasties at all. The only nasty stuff you'll have to handle is the trifluoroacetic acid itself.
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PHILOU Zrealone
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NaF(aq) --> Na(+) + F(-)
2F(-) --> F2 + 2e(-)
2Na(+) + 2e(-) --> Na2
Thus
NaF(aq) -electrocell-> Na2 + F2(g)
HF(aq) -electrocell-> H2(g) + F2
Na2 + 2H2O --> 2NaOH + H2(g)
F2 + H2O --> HF + HOF
HOF --> HO(+) + F(-)
2HO(+) +2e(-) --> H2O2
2HF -e-> H2(g) + F2(g)
2HOF -e-> HO-OH + F2(g)
Thus NaF and HF are producer of F2 but also of H2O2!
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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bio2
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trifluoroacetic acid
Hey Polverone;
Found this old post of yours when doing a search on subject acid.
Preparation of Trifluoroacetic Acid
DONALD RAE ALLEN;
J. Org. Chem.; 1961; 26(3); 923-92
5.
Were you ever able to retrieve the entire article? as it couldn't be found in a search.
If so will you please post it. Thankyou!
TFAA from R143a wow! was just about to buy some and had to lower my order quantity. Ever check the price on this stuff?
It's an arm and a leg for a liter unless you buy the drum which would last me maybe 200 years.
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BromicAcid
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Here you go, enjoy.
Attachment: jo01062a068.pdf (304kB)
This file has been downloaded 1310 times
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bio2
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TFAA from Freon
Thanks for that BromicAcid you're gonna love this one.
Was doing a patent search on the subject and found US5736012 which refs the JOC article. They mention that that procedure is not scalable (compare
the electrode area to the grams produced in a couple hours and it does seem a little pathetic). Apparently though it gave them the inspiration to find
that with a very similar procedure using light (instead HV discharge), water and a catalytic amount of Cl they can get 90+% yields in a few hours from
R143a. It doesn't really seem much more difficult providing you have the ability to make a suitable pressure vessel. They mention that a 500w
mercury vapor lamp is fine instead of their fancy Hanovia unit.
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Chris The Great
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Hmm, could NaF be substituted for HF, or would to many side reactions occur like those mentioned byPhilou? I'm curious because sometime in the
future, when I get my lab somewhat better equipped, I plan on doing some experimentation that requires triflouromethanesulfuric acid. I haven't
seen it sold anywhere. Though I have seen triflouromethane sulfonic acid, but that's a different chemical.
Also, I'm assuming the procedure of making triflouromethane sulfuric acid is very similar to that of triflouroacetic acid:
[CH3OSO3-] + [H+] + e--> H + [CH3OSO3-]
[CH3OSO3-] - e --> CH3OSO3
H3COSO3 + 7F --> F3COSO3F + 3HF
F3COSO3F + H2O --> F3COSO3H + HOF
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Synopsis
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Just pointing out that TFAA stands for trifluoroacetic anhydride. TFA is the correct abbreviation for trifluoroacetic acid.
Your theory is crazy, but it\'s not crazy enough to be true. - Niels Bohr
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FluorinationMan
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Reference for electrocell fluorination reaction
Hi,
I was greatly interested in the preparation of TFA using the electrocell method.
Does anyone have a reference for that reaction?
Thank you
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