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Author: Subject: poor yield - chloroform via haloform reaction
Boffis
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[*] posted on 10-2-2015 at 07:22


@haber

No chance! Rationalise this statement! Consider the way hypochlorites are produced;- for each mole of KOCl produced (90.6g) you get a mole of KCl (75.6g) plus an excess of KOH (say 10 molar % = 5.6g) to stabilise the hypochlorite. If 90.6g =60% then 75.6 =50% plus 5.6g = about 3.7% and then presumably there is some water present too; it being a solution.

See the problem?

@FedeJuninArg. Halogenation of acetone in basic conditions favors rapid 1,1,1 tri-substitution followed by spontaneous fission. Under the condition you propose you get 1,3 and then 1,1,3 etc substitution which does not give the haloform fission on treating with alkali. There are a whole series of papers on these reactions and the complex re-arrangements that the products undergo on the Acta Chem. Scand. web site where all issues of their journal is available for free! Read and thou shalt be enlightened.

[Edited on 10-2-2015 by Boffis]
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Haber
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[*] posted on 10-2-2015 at 10:26


@Boffis
I had to recheck this after your post, it turned out to be 60% calcium hypochlorite.

To my defence, calcium hypochlorite is called Kalciumhypoklorit in my language, and the potassum salt is called Kaliumhypoklorit, I must have misread it ;).

[Edited on 10-2-2015 by Haber]
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aga
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[*] posted on 10-2-2015 at 11:31


Quote: Originally posted by Amos  
I've discussed increasing the yield ... 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.

That's a great idea !

Add a length of hosepipe to the bleach bottle neck, then invert the bottle.
(obviously some sort of stopper or tap/valve would be required.)

Also sorts out the phase separation.

Nice one.




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FedeJuninArg
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[*] posted on 10-2-2015 at 12:08


@Boffis that's interesting..

Could it be possible an exhaustive halogenation 1,1,1,3,3,3- ?
then fission with alkali giving 2 moles of CHCl3 and 1 mole of formate?
maybe letting this react overnight before the alkali addition.
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Boffis
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[*] posted on 10-2-2015 at 17:17


@ Fede

Hexachloroacetone does not yield 2 moles of chloroform because the trichloroacetic acid produced by the loss of one carbon atom is stable. As I have some hexachloroacetone I might give this a try to check this. Intermediate halo ie Di, tri and tetra halo acetones undergo Favorsky's rearrangement. Penta haloacetones give other products and the hexachloroacetone has no alpha hydrogen so will not undergo this rearrangement.

Here are a few of the many relevant refs in Acta Chem. Scand.
Vol 16, 1962 pp2467-2469
Vol 17, 1963 p1472
Vol 18, 1964 pp1998-1999
Vol 19, 1965 pp31-34
Vol 20, 1966 pp253-255; 376-384; & pp862-870

There are many more and these papers contain many references to earlier work. Happy reading!
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FedeJuninArg
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[*] posted on 10-2-2015 at 20:43


@Boffis

You're right, I realised that after sending the comment.
It'd be great if you give a try and then tell us what do you obtain
also I'd try the hexahalogenation.

Thanks bud.. :)
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ahill
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[*] posted on 15-2-2015 at 00:28


Thanks everyone for their input - the stolen mols have been recovered.

As was apparent to a number of posters - the 33% figure on the sodium hyperchlorite was rubbish - I suspect something closer to 3.3% (the manufacturer has not responded to my request for clarification.)

Anyway, I obtained some different bleach - the label says 12.5% - 125g NaOCl a litre - the difference in appearance alone was enough to tell me it was a lot more substantial than the other stuff.

Despite the slanderous assertions to the contrary - my math was good - the only significant mistake was the reliance on the MSDS. Anyway this time I got much closer to an optimal yield - from 4 litres of bleach, and 90g acetone - I figured about the best I could expect would be 127.15g - and I got 90% of that raw, and it dropped to 65% after distillation. (I pinched the distillation off at 62C there was a little something (water?) left behind, and the rig was pretty leaky) - so I am happy enough with that.

I was more careful to keep things cool this time - started at -13C, but it still peaked at 30C - a much bigger rise than last time.

..anyway after a couple of batches, I am now the proud owner of almost 200ml of shimmery shiny chloroform.

So I guess the moral of the story is, "Dont trust MSDSes."

Thanks again.
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