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ahill
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poor yield - chloroform via haloform reaction
Hi - I'm trying to make chloroform from hardware store acetone and sodium hypochlorite bleach. I've just repeated the process and once again have a
yield of perhaps 1/10 of what I calculate the theoretical yield should be.
I'm soliciting suggestions for where I might be going wrong.
My NaOCl is this contractor grade bleach. No contents are listed on the label (aside from 45g/L available chlorine), but the MSDS suggests a whopping 33% sodium hypochlorite with the rest being water.
The acetone, also from the same hardware says 100% acetone on the label.
I used 2 liters of bleach - weighing 2124g - at 33% NaOCl, I figure thats 700.92g, or 9.4 mol. I called it 9, 'cause I've had it for few months, and
I'd rather the NaOCl be in excess.
This online chemical equation balancer seems to suggest (at least to me) that I need 3 mol of NaOCl for each mol of acetone - so 9 mol of NaOCl -
3 mol of acetone - thats 174.24g, or 220.28ml. Lets call it 200, 'cause, as I said, I've had the bleach for a few months ...
So, cooled it all down to less than 10'C - put the bleach container in an ice slurry, added the acetone in two goes with lots of stirring in between -
it didnt go over 25'C
..after sitting for a couple of hours, decanting most of the mother liquid off - I have a bright, clear layer of maybe 50ml sitting in at the bottom
of my seperatory funnel. 50mls ! And thats before distillation ! I've been robbed ! Again ! ('cause this is about what I got last time)
..so I would really appreciate any suggestions. I figure I should be getting 200 to 300g of chloroform. Am I missing something obvious / doing
something wrong ? Is my feedstock suspect - is there a easy way to assay bleach/NaOCl ? I had a quick look on the internet, but the only processes I
found depended on iodine - which I dont have ATM.
Thanks.
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Bot0nist
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Both bbartlog and Magpie reported mediocre yields from this procedure in a haloform thread.
[Edited on 8-2-2015 by Bot0nist]
U.T.F.S.E. and learn the joys of autodidacticism!
Don't judge each day only by the harvest you reap, but also by the seeds you sow.
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ahill
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Yeah - I am actually really jealous of their disappointing results - they are getting something like 4X the yield I am. I want to be disappointed
like that !
Cheers.
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j_sum1
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| Quote: | | No contents are listed on the label (aside from 45g/L available chlorine), but the MSDS suggests a whopping 33% sodium hypochlorite with the rest
being water. |
I believe these two figures are contradictory. Now, I may be wrong because it was just a quick back of the envelope calculation, but I think 33%
sodium hypochlorite works out to be 165 grams of available chlorine per litre.
If the product is the lesser figure, that, by itself will diminish your yield down to a third. Combine that with the same yield problems that
everyone else has and factor in a lower concentration than you were anticipating and you might just have found the problem.
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Amos
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First off, how old is the bleach? Sodium hypochlorite decomposes over time, and the rate of decomposition is faster at higher concentrations of it.
Another question: How long are you allowing this reaction to go? Most bleach contains sodium hydroxide, which as an aqueous solution will happily
destroy your chloroform, instead producing (I believe) sodium formate in solution. I've found that when using about 4L of my 8.25% NaClO and the
corresponding amount of acetone, the optimal time for me to wait to collect the highest yield is about 4-5 hours, and I might collect anywhere from 60
to 75 mL (90 to 113g). My attempts to do the reaction overnight for a period of about 10-12 hours have always resulted in lower yields. An even more
severe cause of decreased yields is not thoroughly cooling your reactants first. Ice-cold acetone and frozen-solid bleach are what I use; on one
occasion I was impatient and only let them go to maybe 5-10 C and a good deal of the chloroform boiled out during the reaction.
I believe in an earlier thread, little_ghost_again had to add large amounts of NaOH to get his reaction to begin and proceed smoothly, but he was
using isopropanol rather than acetone for his version of the haloform reaction(which is usually meant to take place in basic conditions, hence the
NaOH). I would suggest experimenting with your reaction conditions a bit and possibly adding NaOH, which may or may not already be in your bleach.
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TheChemiKid
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Are you sure the bleach is 33%? I haven't heard of bleach above 12.5% that doesn't decompose instantly.
When the police come
\( * O * )/ ̿̿ ̿̿ ̿'̿'̵͇̿̿з=༼ ▀̿̿Ĺ̯̿̿▀̿ ̿ ༽
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Boffis
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@ahill; No you haven't been robbed! Read some of the earlier threads and look at the formulas with care!
I have calculated from the data you have presented that the maximum possible yield in your case is 17.9ml of chloroform per liter of bleach assuming
100% efficiency and that chloroform is totally insoluble in water (which it isn't but very sparingly soluble so a reasonable assumption). Therefore
starting with 2 liters of bleach and getting 50ml of raw product is impressive because thats >100%. Your theoretical yield is only 35.8ml or 53.3g
(density of chloroform 1.49).
Also remember the solubility of chloroform in water is about 8g/L (bromoform 3g/L) but this is greatly reduced by adding brine or carrying out the
reaction in the presence of salt or calcium chloride. I don't do this in my bromoform preparations because the salt loading of the final solution is
high anyway but you may find that you can improve your chloroform yield slightly by adding 100-150g of salt per litre to the reaction mixture.
This is based on the label's claim that your bleach is 45g/l available chlorine. So assuming that they calculate available chlorine on the following
basis (and its a useful one for our case):
NaOCl + 2H+ -> Na+ + H2O + Cl
Your bleach when new contained about 94.4g/L of NaOCl. Assuming the reaction of this with acetone proceeds according to the following equation:
17NaOCl + 7C3H6O -> 9C2H3O2Na + 8NaCl + 3CHCl3 + 6H2O
You can see that 94.4g of NaOCl yields 26.7g of chloroform (or 17.9ml)
So you haven't been robbed its just your dodgy maths!
By the way I have never done the chloroform reaction but I have made large amounts of bromoform and iodoform by the analogous reactions using bleach
and the appropriate halide. I always analyse my bleach before I use it and base my calculations on the actual hypochlorite content. I purchased a 5L
can of bleach form a the local janitorial products supplier about 2 years ago, it claimed to be 14-15% hypochlorite and my analysis found 15.18%. In
January this year I used up the remainder, now the analysis revealed 12.41%. So as several earlier posters have alluded to, there is a significant
loss of strength with time.
[Edited on 8-2-2015 by Boffis]
[Edited on 8-2-2015 by Boffis]
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Amos
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Yeah, the numbers Boffis has given sound a lot more plausible; I think the 33% NaClO figure is just a blatant lie or bad math on the company's part;
more likely the 45g/L is the correct figure, as it would fit with the general trend of "concentrated" bleach being sold at 8 - 12.5% concentration.
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Amos
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Yeah, the numbers Boffis has given sound a lot more plausible; I think the 33% NaClO figure is just a blatant lie or bad math on the company's part;
more likely the 45g/L available chlorine is the correct figure, as it would fit with the general trend of "concentrated" bleach being sold at 8 -
12.5% concentration.
[Edited on 2-8-2015 by No Tears Only Dreams Now]
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blogfast25
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Good work, boffisman!
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S.C. Wack
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Chloroform is the least of your problems. If the label says 45 g available Cl in a liter (95% of the NaOCl %), why would you think there is 700.92 g
in 2 liters, regardless of what the MSDS does or does not say, especially when 33% solutions of hypochlorite are not sold by anyone.
Chloroform yields may vary from run to run.
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Hawkguy
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How can Chloroform be extracted from an aqueous solution then? Maybe an addition of a KOH or NaCl sat. solution could work, and make for a larger
yield...
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aga
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5L Bleach bottle in Freezer overnight, add acetone, keep as cool as possible 1 more overnight.
Day after, decant off 90% of the liquid, stick the rest in a sep funnel.
The bit at the bottom is your crude chloroform.
Distill, yielding even less, but purer, choloroform.
Add 1w% pure ethanol to stabilise it or phosgene might evolve over time, and kill you, literally.
If stored for a long time, distill again before use.
Edit:
Yield is low with this method, so do not expect more than maybe 50ml.
Practice and experimentation helps achieve a slightly less poor yield.
[Edited on 8-2-2015 by aga]
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ahill
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thanks for the input everyone. I'll give it another whirl using bleach from somewhere else - in the meantime I have contacted the distributor and
asked for clarification on the accuracy of their MSDS.
Boffis - how did you analyze the hypochlorite content of your bleach ?
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blogfast25
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Quote: Originally posted by aga  | Add 1w% pure ethanol to stabilise it or phosgene might evolve over time, and kill you, literally.
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A little context and perspective, please. To generate enough phosgene to kill one from degrading chloroform would take rather a lot of haloform
reaction. Don't equate the use of phosgene as a war gas with a lab killer...
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Amos
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I just want to comment on aga's method: You're probably only getting 50mL max because you let it sit for two whole days; by that point a huge amount
of the chloroform will have already been decomposed.
I've discussed increasing the yield in the haloform reaction with another member of the forum by using a container that has a very narrow bottom, so
as to limit the contact area between the upper NaOH solution and the lower chloroform layer. Not sure how much difference this will make, but if
couldn't hurt if anyone wants to try it.
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FedeJuninArg
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Why don't you make you're own hypoclorite in situ? Chlorine gas (from TCCA and HCl) into acetone, Ca(OH)2 or Na(OH) and some water.
I'll do it tomorrow and then i'd tell how it's gone.
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Amos
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@FedeJuninArg You might want to re-think that; channeling chlorine directly into acetone might lead to the formation of at least some
chloroacetone, and I doubt you want to be dealing with even a little bit.
[Edited on 2-9-2015 by No Tears Only Dreams Now]
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Boffis
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@ahill, I have some further bad news for your yield!
According to the attached data sheet from Solvay Chemicals International the % derived from the "Active" chlorine is half what I had estimated! I
don't understand how they reach their figures but if you look at the last page you will see that there is a formula that relates % NaOCl to % Active
Cl but the ratio implies that 1 Mole of NaOCl generates 1 Mole of Cl2 which is rubbish. The only way this can happen is if you react the hypochlorite
with hydrochloric acid. If you rearrange the formula so that it give Active Cl = you get:
A (active Cl) = % NaOCl x71/74.45
The only way this would work is via this equation
NaOCl + 2HCl = NaCl + Cl2
but since we are considering an alkaline environment this doesn't apply and the equation I gave in my earlier post is the correct measure of available
Cl in your environment but it means they are effectively claiming doubled the real amount of Cl in the bleach. Interestingly this is how "available
chlorine" is estimated on bleaching powder and this may explain why many posters have posted poor yields.
This basically means that you only have about 4.7% NaOCl in your bleach, which is nats-piss weak, and your theoretical yield is therefore only half ie
13.35g of chloroform per litre of bleach and as much as 8g of this may be left in the aqueous phase!!!! (In reality the salt in the bleach will reduce
the solubility of chloroform in the waste liquor but you are going to lose a significant amount even if its solubility is halved. Sorry about the
extra extra bad news!
A suggestion; buy yourself some "proper stuff" 14-15% bleach and use it quickly! I would also suggest getting yourself a burette and some high quality
sodium thiosulphate so you can measure the true strength of your bleach.
Attachment: Hypochlorite density & data tables.pdf (47kB)
This file has been downloaded 2183 times
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Amos
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Boffis, how could ahill have obtained 50mL of product, then, if this is true?
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Boffis
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I don't know. The data sheet I attached is from just one of many producers so possibly the source of ahill's bleach uses a different definition for
active chlorine more similar to my original assumption.
The other factor is that ahill believing his bleach to be much stronger than it was probably added too much acetone and the presence of much salt in
the bleach may be sufficient to cause much of the acetone to partition into the organic (chloroform) phase. This is speculation but it is not without
precedence.
@ahill how much acetone did you add and have you distilled the product yet and if so how much distilled over at low temperature?
By the way I have just noticed that ahill gave us the density of his bleach; he says 2l weighed 2124g = 1.062. according to the table in the
attachment above is about 4.4% NaOCl very close to value calculated from the available chlorine via the 2nd (dodgy) method!
[Edited on 9-2-2015 by Boffis]
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gardul
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I would also like to make a note about keeping the sodiumchlorite COLD. Make sure it is at least 0C. I prefer right around -10C. I've had decent
results this way.
[Edited on 9-2-2015 by gardul]
I just made you read this very pointless signature. How does it feel?
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FedeJuninArg
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| Quote: Originally posted by No Tears Only Dreams Now | @FedeJuninArg You might want to re-think that; channeling chlorine directly into acetone might lead to the formation of at least some
chloroacetone, and I doubt you want to be dealing with even a little bit.
[Edited on 2-9-2015 by No Tears Only Dreams Now] |
You're right, but here chlorine must be really in excess. Chloroacetone is always the first product.
I'm still thinking this is the best method as Cl2 disproportionation in basic aqueous media is instantaneously.
Another way is the same as preparing chloroacetone, but with TCCA 3X excess or more, 1ml conc. H2SO4, 1ml 6M HCl and some water in ice bath, all in
and big flask (500ml at least).
Note that all the HCl is consumed by the TCCA and then regenerated again; so putting an small amount of it will make the reaction slower. Finally
adding NaOH so the CHCl3 releases.
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Amos
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| Quote: Originally posted by FedeJuninArg | | Quote: Originally posted by No Tears Only Dreams Now | @FedeJuninArg You might want to re-think that; channeling chlorine directly into acetone might lead to the formation of at least some
chloroacetone, and I doubt you want to be dealing with even a little bit.
[Edited on 2-9-2015 by No Tears Only Dreams Now] |
You're right, but here chlorine must be really in excess. Chloroacetone is always the first product.
I'm still thinking this is the best method as Cl2 disproportionation in basic aqueous media is instantaneously.
Another way is the same as preparing chloroacetone, but with TCCA 3X excess or more, 1ml conc. H2SO4, 1ml 6M HCl and some water in ice bath, all in
and big flask (500ml at least).
Note that all the HCl is consumed by the TCCA and then regenerated again; so putting an small amount of it will make the reaction slower. Finally
adding NaOH so the CHCl3 releases. |
Alright, as long as you know the risks and think you're prepared to handle it with the equipment you have available, by all means proceed. I just know
that I'd be evicted from the home if I ever tear gassed my family.
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Haber
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I think Ive seen bottles of 60% potassium hypochlorite OTC.
[Edited on 10-2-2015 by Haber]
[Edited on 10-2-2015 by Haber]
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