MeshPL
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Chloroacetic acid as chlorate cell additive
Hello everybody!
In typical chlorate cell with graphite electrode you want pH control. For obvious reasons, HCl is pretty much always used.
But I had an idea while reading Woelen's site:
http://woelen.homescience.net/science/chem/exps/precision_electrolysis/index_acetate.html
("Chloroacetate instead of acetate, totally different reaction!" section)
Generally speaking I'm considering using chloroacetic acid for pH control. The overall reactions, it will undergo, are as follows:
Cathode:
CH2ClCOOH + H+ + 2e- --> CH3COOH + Cl-
The following reaction will contribute to increasing pH, but may only happen whan chloroacetic acid is undissociated-at low pH. Acetic acid is
somewhat weak and will not dissociate enough to compensate for H+ ions used.
Anode:
CH2ClCOO- + H2O - 4e- --> CO2 + CO + 4H+ + Cl-
CH2ClCOO- + 2H2O - 6e- --> 2CO2 + 4H+ + Cl-
CH2ClCOO- + 2H2O - 4e- --> HCOOH + 4H+ + Cl-
When pH is high dissociated chloroacetic acid will be oxidised to carbon oxides (or formic acids) and chloride ion. The pH won't decrease too much,
because the same amount of hydrogen ions will be reduced to H2 at the cathode, by example:
CH2ClCOO- + H2O --> CO2 + CO + 2H2 + Cl-
This means nearly no pH decrease, however Cl- is much less likely to accept proton and work as conjugate base.
Assuming both chloroacetic acid oxidation and reduction happen simoultaneously at some pH, pH will likely decrease:
3CH2ClCOOH + CH2ClCOO- + 2H2O --> 2CO2 + 3CH3COOH + 3HCl + Cl-
Acetic acid may undergo Kolbe electrolysis or simmilar oxidation. This also means acetic acid produced in reactions will not likely cause too much
harm.
I don't think theese reactions will happen too much, because of already present Cl- ions. (After all we are producing chlorates) and not a lot of
chloroacetic acid will be used in process.
To sum up:
At low pH chloroacetic acid will be reduced, reaction will cause increase in pH. (Chlorine will be oxidised, what will even further increase pH)
At high pH chloroacetic acid will be oxidised, H+ ions will be produced, but the same amount will be oxidised. pH may decrease slightly.
At some point both processes may happen, than pH may decrease since acetic acid will be produced and no other acid will be used.
Products of theese reactions shouldn't harm chlorate production, because carbon oxides will be removed from the cell, chloride ions are actually used
in chlorate synthesis, while carboxylic acids SHOULD be easily oxidised to water and CO2 or something else.
Questions:
What is said low/high/some pH?
How much chloroacetic acid will be consumed?
Will chloroacetic acid interfere in chlorate production?
Will di/trichloroacetic acids form?
Will acetic and formic acids be easily oxidised?
What are potentials of this reactions?
What ph will reactions stabilise at so that ph wouldn't change?
Any ideas?
[Edited on 17-5-2015 by MeshPL]
[Edited on 18-5-2015 by MeshPL]
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AJKOER
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I happen to incidentally make some chloroacetate while running a galvanic cell (the action of Al and Cu on HOCl which was prepared impurely by mixing
chlorine bleach and vinegar). The cell reaction, which forms chlorine that in the presence of Cu/CuO and sodium acetate in a few days appears to
produce what I found to be a quite nauseaous smelling compound (even in low exposure doses while working outside no less).
Further research confirms my suspicions, to quote Wikipedia http://en.m.wikipedia.org/wiki/Chloroacetate :
"Safety
Like other chloroacetic acids and related halocarbons, chloroacetic acid is a hazardous alkylating agent. The LD50 for rats is 76 mg/kg.[3]
Chloroacetic acid easily penetrates skin and mucous membranes and interferes with cellular energy production. Initial dermal exposure to high
concentrations (e.g., 80% solution) may not appear very damaging at first, however systemic poisoning may present within hours. Exposure can be fatal
if greater than 6% body surface area is exposed to chloroacetic acid. "
I now avoid this preparation for HOCl for use in the cited galvanic cell reaction, as in my opinion, it is just too nasty (and this is from a guy who
likes chlorine).
I would advise you to rethink your experimentation with this acid.
[Edited on 18-5-2015 by AJKOER]
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MeshPL
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Well, this doesn't sound like it is a very safe compound to deal with. However, it's solid in room temperature, and with some safety precautions (good
gloves), I should be fine. Also, I'm not going to use a lot of it, and I'm using chlorate cell with pipe for safe gas removal.
Hydrochloric acid and hexavalent chromium are not the safest compounds either.
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AJKOER
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A few points, I hope you will consider.
First, it is the longer term effect of inhaling halocarbons I am concerned about assuming ones avoids a rapid death by direct physical contact
although the compound fumes did apparently make me feel, or think I was, going to be sick.
Second, electrolysis is a slow process over days and any warming will result in fume generation.
Third, it is one thing when you are OK with the risk, but could others be exposed as well?
Fourth, noxious fumes don' t endear neighbors and could produce unwanted attention.
Last, I have demonstrated on this forum alternatives including the power of photolysis in a safe closed system as well as in an energy efficient
manner to produce chlorates (see, for example, http://www.sciencemadness.org/talk/viewthread.php?tid=34429 ). I also find the photochemistry reactions themselves interesting and educational
with possible applications to water purification.
[Edited on 18-5-2015 by AJKOER]
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jock88
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HCl is not very hazardous if diluted.
There is not need for the chromates as they only contribute a small increase in yield.
There are easier ways for the chlorate buff to obtain better yield than messing with chromates.
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MeshPL
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Fumes? Neighbours? This acid would have to have extremely strong odour for my neigbours to smell it and not think it's vinegar.
Also, little CH2ClCOOH would escepe from the cell, through the carbonate solution buffer.
Not to mention the fact that nearly no other halocarbons are produced.
Also, from the theoretical site, could the proposed mechanism for pH regulation and CH2ClCOOH destruction in cell work?
It's quite funny that, here where I live, you can buy such a dangerous chemical that easily. But try to buy HCl... at least they sold me it in a
welding shop.
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woelen
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I would not worry at all. AJKOER's warning is purely theoretical. Of course, 80% solutions of the chemical are nasty and must be treated with care,
but if a gram or so is dissolved in a liter of water, then I would not worry at all. The neighbours certainly will not be affected in any way. Of
course, you should not stick your nose in the bottle with the liquid, but if common sense is used, then the experiment can be performed safely.
Whether the acid increases the efficieny of the cell is to be seen. There are two kinds of inefficiency. One is the pH-dependent one, which can make
the difference between 6 electrons per chlorate ion (100% yield) and 9 electrons per chlorate ion (66.7% yield). See my webpage for more info. The
other kind of inefficiency is MUCH worse, and that is the re-reduction of chlorate (and hypochlorite) at the cathode. This can lead to very low
efficiency, such that nearly all current is converted to heat and you only have wear of the anode without decent production of chlorate.
There may be other compounds than chromates/dichromates which keep the cell efficient, but adding no suitable compound or adding a small amount of
chromate makes a tremendous difference! With the chromate I also would not worry too much. The danger of chromates is exaggerated a lot these days. Of
course, avoid inhalation of fine dust, or droplets with chromate, but if you get some on your skin, and rinse away the liquid quickly, then there is
no real issue. It is not instant death in a bottle. The only thing you must avoid is that many small droplets of liquid escape from the bottle. The
bubbling at the cathode can lead to formation of many small droplets. Use a good cap and if you still think some droplets escape, cover the jar with a
paper tissue. This is very effective in keeping small droplets behind, while allowing gas to escape.
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gatosgr
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How about the carcinogenic part?
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jock88
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I do not think that adding chromates makes a huge difference to current efficiency. If you have a sensibly sized cathode it will make little or none
that you will notice unless you are measuring ce with good accuracy. A few % perhaps. A few % is very important if you are making industrial amounts
of course.
Chromates work by putting a film on the cathode which effectively reduces the surface area of the cathode are there for raised the current density on
the cathode. The same effect can be had if you use a small cathode. This will give a very small increase in cell voltage which is usually irrelevant
as most people are using rather inefficient power delivery set up anyways. Adding compounds complicates things. Stay green
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MeshPL
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| Quote: |
Woelen said
Of course, 80% solutions of the chemical are nasty and must be treated with care, but if a gram or so is dissolved in a liter of water, then I would
not worry at all. The neighbours certainly will not be affected in any way. Of course, you should not stick your nose in the bottle with the liquid,
but if common sense is used, then the experiment can be performed safely.
Whether the acid increases the efficieny of the cell is to be seen. There are two kinds of inefficiency.
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Emm... CH2ClCOOH is solid. It is CHCl2COOH which is liquid. However CH2ClCOOH is well soluble in water, up to... ~46%??? According to wikipedia page
it's solubility in water is 85.8g per 100ml of water in 25C, so saturated solution isn't even 50%. Thanks wikipedia...
So anyone has an idea, if it will surely (not) work? I will check it, but what for, if it will surely not work...
I'll post results after some time.
There is third kind of inefficiency, also pH dependent one called: anode errosion. 
| Quote: |
Gatosgr said:
How about the carcinogenic part?
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I've read, that chloroacetic acid is not known to be carcinogenic to humans or mice:
http://www.epa.gov/ttnatw01/hlthef/chloroac.html
Also, I should be able to use KH2PO4 as buffer to stabilise pH?
[Edited on 18-5-2015 by MeshPL]
[Edited on 18-5-2015 by MeshPL]
[Edited on 18-5-2015 by MeshPL]
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gatosgr
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I'm talking about chromates.
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MeshPL
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Ok. Chromates ARE carcinogenic.
Trivially, I'm gonna use chromic anhydrde as Cr(VI) source. Still carcinogenic.
[Edited on 18-5-2015 by MeshPL]
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papaya
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Addition of organic material may ruin your anode quickly (MMO, expensive), also decomposition of this organic material will produce all kind of other
substances contaminating solution,degrading anode and lowering yields due to concurring reactions at anode, IMHO.
[Edited on 18-5-2015 by papaya]
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MeshPL
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I'm using graphite, not MMO. The only way I could buy MMO, here where I live, is to buy it in the US and pay a lot for delivery.
I don't think organic material will cause graphite erosion, will it?
Speaking of contamination:
a) homemade chlorate is never very pure anyway.
b) electrolysis shuold destroy chloroacetic acid and it's products.
c) I don't think potassium chloroacete is so unsoluble to be impossible to wash it out of chlorate product together with chlorides.
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jock88
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Where do you live?
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j_sum1
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Quote: Originally posted by MeshPL  | I'm using graphite, not MMO. The only way I could buy MMO, here where I live, is to buy it in the US and pay a lot for delivery.
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I bought an MMO electrode from a member here. It was 2" by 6" and fitted in a regular envelope for regular postage.
The electrode was under $10US and the postage was less than that again (US to Aus), so it wasn't a huge outlay. It arrived promptly too.
I will see if I can fish up the details for you, but it is likely that someone will actually beat me to it. He sells regularly to SM members and has
a SM discount.
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woelen
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@jock88: My experience with adding chromate to an electrolysis cell is that it makes a huge difference. Without chromate, the yield is really pathetic
(at most 10% current efficiency, probably even less). With chromate added, the yield is somewhere around 60% or so, which is not bad for a simple
home-made cell.
@MeshPL: Homemade chlorate can be very pure, you can make it better than the grade which is sold by pyrotechnics suppliers. If you use graphite, then
it is hard to obtain a nice white product, because the ultrafine carbon particles are very hard to filter. If you use MMO, then you can get snowwhite
large crystals of very pure KClO3 by simply recrystallizing. Any yellow chromate/dichromate and any chloride is easily separated, because of the
excellent recrystallization properties of KClO3. I myself made appr. 250 grams of very pure KClO3 from KCl and a tiny amount of K2Cr2O7.
Separating from chloroacetic acid will be without problem, due to the huge difference in solubility.
I doubt, however, whether adding CH2ClCOOH does anything good to the electrolysis process. I expect that it does no good, nor harm, but then you'd
better leave it out, it is an expensive and hard to get chemical, which better can be used for other purposes. But if you really want to do the
experiment, feel free to do it, I see no high risks in it, other than losing some of your nice CH2ClCOOH.
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MeshPL
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CH2ClCOOH is hard to get? Here in Central Europe, I can easily buy some, and it is 4$ per 250g. For comparison, 500g of CuSO4 is about 4$ here, from
the same supplier.
I don't think I need that MMO. Graphite is ok (I do not need extrenely pure KClO3), and I can buy decent graphite rods for 1$ each and I can make 3
electrodes from each one. Gouging rods are even cheaper: 0,25$ per one.
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papaya
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If you are THAT determined to try this and test/prove your arguments, I'll suggest that you run two chlorate cells connected in series(one with plain
NaCl, other with your additive, all conditions maintained equal), so the same amount of charge passes through both cells and then weigh you products
to see the difference. Don't forget to report back!
[Edited on 19-5-2015 by papaya]
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MeshPL
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Two chlorate cells... well I don't have materials. But I latter on I may try to create a mini chlorate cells with single electrodes and compare pH's
and graphite erosion in both of them. My goal with CH2ClCOOH is not higher efficiency, but possibility of use as pH regulator.
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