Stibnut
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Iodoform problem
I've been playing around with the haloform reaction. Obviously the basic synthesis of chloroform with acetone and bleach is easy: just chill the
bleach to ~0 C, pour it into a glass container in an ice bucket, calculate the amount of acetone you need, mix them, and voila. I made bromoform in
much the same way, except that I added NaBr (in a concentrated solution) to NaClO to get NaBrO, then added acetone and made it in the same way. Dried
them both with MgSO4 and stored in amber bottles. I like bromoform even more than chloroform - it is dense and smells like butterscotch or caramel to
me, not just a sickly sweet smell like chloroform. I won't put it on my ice cream though.
Today I attempted the same sort of reaction to make iodoform. I dissolved KI in some distilled water and added it to bleach with a slight excess of
KI, presuming that I'd get NaIO like I got NaBrO. The solution briefly took on the reddish color of iodine, then changed to a yellowish amber color.
Then I added the acetone and the color went away. But instead of getting dense yellow crystals of iodoform precipitating out of the solution, I got a
white and fluffy-looking solid, which precipitated out rather slowly with only a slight temperature increase: it got only 1.5 C warmer rather than the
30-35 C increase I get with chloroform and bromoform synthesis.
I have no idea what went wrong, nor what the white solid is. Can anyone tell me what I made and why it formed in lieu of iodoform?
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DraconicAcid
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Whenever I've made iodoform, it's been a pale yellow powder.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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MeshPL
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Maybe you didn't add enough KI? You need quite a lot, more than a half more in terms of weight. Or maybe your iodine disproportionated in basic
enviroment to NaI and NaIO3?
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Stibnut
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I'll make a more quantitative post on what I did.
I dissolved 20.0 g KI into 26 mL of distilled water. That's 0.1205 mol KI, so I needed the same amount of NaClO, which comes out to 8.97 g. The bleach
I was using is 8.25% NaClO, so that's 108.7 g bleach. I deliberately added a little less than this so it would be the limiting reagent and I wouldn't
get chloroform or anything. The amount I added was 104.4 g. There was a very brief flash of brown-red iodine color, which rapidly turned into a deep
amber yellow.
Then I calculated the amount of acetone I'd need: 1/3 the number of moles of KI, or 0.0402 mol = 2.335 g. I weighed out 2.370 g on a milligram scale
and added it. The yellow color disappeared and the fluffy white stuff began to precipitate out slowly, accompanied by a temperature increase of only
1.5 C rather than the 30+ C that I had been expecting. Checking it the day after, there's nothing yellow there at all, so I definitely didn't make
iodoform. Maybe it did disproportionate into NaI+NaIO3?
NaI would definitely have stayed in solution given that there were ~120 mL of water. But NaIO3 has a solubility of only 8.08 g/100 mL, so it would
precipitate. Then I found this on its wiki page:
| Quote: | Sodium iodate can be oxidized to sodium periodate in water solutions by hypochlorites or other strong oxidizing agents:
NaIO3 + NaOCl → NaIO4 + NaCl |
Checking the solubility of NaIO4, it's only 10.3 g/100 mL, so I would expect some of it to precipitate out like with NaIO3. It sounds like I created
NaIO4 via NaIO3, with maybe some unreacted NaIO3 sticking around in the precipitate as well, and probably some KCl and NaI remaining in solution. Does
this make sense?
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PHILOU Zrealone
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Aceton is known solubilizator of NaI.
Aceton is known to be able to solubilize Na perchlorate better than chlorate better than chloride...while the solubility in water is the other way
arround...so there is a chance NaIO3 and NaIO4 follow the same patern...
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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Stibnut
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Turns out it works very well if you just reverse the order of the acetone and the hypochlorite. When I added the acetone to the KI solution first and
then added the NaClO after that, the reaction worked like a charm, producing some nice pale yellow iodoform rapidly in an appropriately exothermic
reaction.
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