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ahill
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sad.gif posted on 7-2-2015 at 23:34
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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[*] posted on 7-2-2015 at 23:50


Both bbartlog and Magpie reported mediocre yields from this procedure in a haloform thread.

[Edited on 8-2-2015 by Bot0nist]




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ahill
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[*] posted on 8-2-2015 at 01:07


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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[*] posted on 8-2-2015 at 03:18


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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[*] posted on 8-2-2015 at 04:40


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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[*] posted on 8-2-2015 at 05:12


Are you sure the bleach is 33%? I haven't heard of bleach above 12.5% that doesn't decompose instantly.



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Boffis
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[*] posted on 8-2-2015 at 07:22


@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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[*] posted on 8-2-2015 at 07:58


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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[*] posted on 8-2-2015 at 07:58


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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[*] posted on 8-2-2015 at 08:04


Good work, boffisman!



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[*] posted on 8-2-2015 at 08:18


Quote: Originally posted by ahill  
45g/L available chlorine)
...
33% sodium hypochlorite


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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[*] posted on 8-2-2015 at 12:10


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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[*] posted on 8-2-2015 at 12:52


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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[*] posted on 8-2-2015 at 14:47


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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[*] posted on 8-2-2015 at 18:55


Quote: Originally posted by aga  
Add 1w% pure ethanol to stabilise it or phosgene might evolve over time, and kill you, literally.



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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[*] posted on 8-2-2015 at 19:17


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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[*] posted on 8-2-2015 at 19:54


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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[*] posted on 8-2-2015 at 20:10


@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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[*] posted on 9-2-2015 at 08:58


@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 1141 times
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Amos
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[*] posted on 9-2-2015 at 10:40


Boffis, how could ahill have obtained 50mL of product, then, if this is true?



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[*] posted on 9-2-2015 at 11:18


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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[*] posted on 9-2-2015 at 12:34


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]




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[*] posted on 9-2-2015 at 21:12


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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[*] posted on 10-2-2015 at 03:41


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.


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[*] posted on 10-2-2015 at 03:44


Quote: Originally posted by TheChemiKid  
Are you sure the bleach is 33%? I haven't heard of bleach above 12.5% that doesn't decompose instantly.


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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