psychοtic
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Regarding the haloform reaction
Now I know this topic has been discussed to both death and the dismay of the most seasoned ones... A consequence of this is that it is really hard to
navigate through all of the information, so I hope you can forgive me. To attenuate the gravity of my violation of the 2nd commandment viz. "thou
shall UTFSE", I placed this in Beginnings. To the point!
So I'm thinking of giving the infamous reaction of hypochlorite and acetone to yield chloroform a go. I watched some YouTube videos and at least one
of them was so casual so as to merely pour the appropriate amount of acetone in the very bleach container and let stand over night—modulo
precautions taken to deal with the exotherm, e.g. cooling bleach and acetone to 0 °C beforehand, occasionally ice salt bath, etc., of course.
Now... on Rhodium's page on this matter, it is mentioned that in the theory, 6 moles of hypochlorite are required for each mole of acetone—is this
correct?, I'm trying to understand the theory behind here, so I know what I'm doing; Wiki wasn't of much help since it mentioned the haloform reaction
as a reaction of a methyl ketone (so far so good)... with X_2 and base, which left me wondering how then our hypohalites substitute for those, but I
digress...
Well, if the above is correct, then I foresee that to get myself a few tiny mills of halomethane, I'd need a shit ton of bleach. This turns me off a
bit—I like to keep everything within the reach of a 250 ml flask. Naturally then I started to consider alternatives: calcium salt. What does "65%
active/free chlorine" means? I heard that it was a measure of antibacterial efficiency when compared to chlorine (100%), is this correct? It does not
mean purity right? It's HTH shit.
Now, now... Here's the procedure I am envisioning: to a suitable vessel containing x mol acetone, there were ever so slowly added 3x mol Ca(ClO)_2 at
a rate such that things did not get out of control.
Alternatively, I heard water is required for our reaction. So then I could of course beforehand prepare a Ca(ClO)_2 sol'n in water and drip that in.
Any thoughts? Am I missing anything? Perhaps calcium hypochlorite is a bitch to dissolve in water or releases chlorine gas thereupon?
Thanks guys and I promise my next post will be better 
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JnPS
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The problem with using Ca(OCl)2 is the calcium salt that forms as a byproduct usually forms a slush instead of a solid precipitate. The sodium salt
dissolves and stays in the water, but the calcium salt just makes the workup a real pain. I can't remember offhand if the byproduct is the alkali
metal hydroxide or acetate, either way, calcium salts are generally less soluble than sodium salts of the same anion if IIRC.
I assume distilling off the reaction mixture may be possible to separate the chloroform, but the ending mixture is basic and chloroform is prone to
degradation in hot, basic conditions.
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psychοtic
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Mm. Interesting. According to Rhodium, it is both the acetate and the hydroxide that are formed, by the way.
Distillation sounds like a good idea... Let me see if I am understanding correctly... The post reaction mixture consists of water, wherein chloride,
hydroxide and acetate of Na/Ca are dissolved/poorly dissolved, and a bottom layer of chloroform, right? Now we distill off the chloroform, perhaps
unreacted acetone comes along but that's another subject. Now, what do you mean by the chloroform being basic? How did those hydroxide ions got
carrier over? And then, couldn't we merely neutralize and redistill?
EDIT: Oh! Never mind that last one! You meant that the reaction mixture, whence the chloroform was to be distilled was basic, and that this basic
character plus the heat required for distillation would degrade the CHCl_3, correct? Well, if that's so... Can't we just neutralize the reaction
mixture prior to distillation? At any rate such would also be a problem in the case where the sodium salt were employed, unless you resigned to manual
separation of the chloroform layer?
[Edited on 3-4-2017 by psychοtic]
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XeonTheMGPony
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Go with the calcium salt, it is superior results and very easy to control.
Cleaning is as easy as a bit of soapy warm water then a HCL rinse
I've used both methods and by far prefer the calcium salt method.
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psychοtic
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I am tending towards the calcium salt as well... So what do you think of this procedure: add a solution of Ca(ClO)2 in water slowly to the acetone;
work-up: neutralize rxn mixture with acid, distill off chloroform.
BTW you know what that 65% free/active chlorine figure means?
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XeonTheMGPony
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you grind the hypoclorite salt in 250ml water, add to flask and set up a reflux.
Slowly add chilled acetone down reflux condenser, if reaction doesn't kick off mildly warm.
Add acetone at a rate to keep the reaction going steady.
Once all acetone is added reflux for 5 minutes to push reaction to completion then distill chloroform.
Take the distilled acetone and wash in a mild bicarb water solution.
Decant chloroform and dry over CaCl, decant to new container with fresh CaCl, and add 1% by mass of dry Methanol or dry ethanol.
Store in dark cool place, I recommend amber bottles
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Boffis
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I think the reaction is generally given as:
3NaOCl + C<sub>3</sub>H<sub>6</sub>O → C<sub>2</sub>H<sub>3</sub>O<sub>2</sub>Na
+ 2NaOH + CHCl<sub>3</sub>
So that's 3 hypochlorite to one acetone. Only one of the methyl groups in acetone will undergo the haloform reaction the rest is converted into
acetate ions.
You will see that NaOH is formed in this reaction which can react with chloroform on heating therefor if you are going to distil it you may need to
neutralise the hydroxide first.
I seem to remember reading on this forum that you can generate sodium hypochlorite by treating bleaching powder with sodium carbonate solution. Or you
could just used the calcium salt to generate chlorine and pass this into sodium hydroxide solution to prepare the sodium hypochlorite first.
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Melgar
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Try this one:
http://www.sciencemadness.org/talk/viewthread.php?tid=73182
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psychοtic
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@ Boffis
That's an interesting observation, that one that only one of the methyls of acetone reacts to form chloroform. At the Rhodium article (https://erowid.org/archive/rhodium/chemistry/chloroform.html), it is given that we need 6 ClO– for each acetone; perhaps this person thought
that both methyls of acetone went on to be chlorinated? Here's the equation they give:
CH3COCH3 + 6 NaOCl -> CHCl3 + NaCH3COO + 2 NaOH + 3 NaCl
Does anyone have any bona fide references for which one is correct?
@ Xeon
Why is the reflux necessary? I thought this reaction was highly exothermic and set off on its own.
Mm, and thanks Melgar. I see I already got plenty pf different methods to try out this evening.
[Edited on 3-4-2017 by psychοtic]
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XeonTheMGPony
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Re fluxing just encourages every thing to finish off
https://erowid.org/archive/rhodium/chemistry/chloroform.html
Followed this with excellent results.
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Melgar
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The easiest and cheapest is the cold sodium hypochlorite one, for sure. The only downside is the large volume, which is mitigated by the fact that
chlorine bleach is only about $2 a gallon. If you need to use a smaller reaction vessel, you can fill it with cold hypochlorite solution, do the
reaction, decant as much of the top layer as possible, fill with bleach again, then repeat until you're out of bleach. By adding a few grams of NaOH
beforehand, you can minimize contamination, and shouldn't need to distill the chloroform for most uses. It is very easy to distill though, so there's
no reason not to.
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Boffis
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A few points of interest here. While I have never intentionally carried out the haloform reaction to produce chloroform I have had a small amount of
chloroform form when using sodium hypochlorite as an oxidizing agent in organic reaction (see may thread on SM on the oxidation of malic acid to
malonic acid). I have, however, made a great deal of bromoform using several different methods but there are a few common features: the best yields
are obtained in the cold, the addition of salt and/or the neutralisation of the excess alkali reduces the solubility of the haloform in the reaction
mixture, when the reaction is over carry out the work-up quickly (don't leave overnight) and don't heat or reflux the reaction mixture to "complete"
the reaction it unnecessary.
And Physcotic, the references you request about the stoichometry of the reaction have been posted before on this forum, it all out there you just have
to look!
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byko3y
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Or you could just redistill the chlorine, which will ensure you have no chlorate in your solution. Making hypochlorite just before use and/or storing
it in cold is pretty much the only way to get a concentrated solution (10% and more).
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