yellow KI?

[YT2095]

the strangest thing seems to have happened whilst making some KI.

 

I used Tincture of Iodine (2.5% KI, 2.5% I and the rest made up with Ethanol).

and a KOH soln.

 

titrating to the clear color I added a tiny excess of the Iodine tinct, as I`ve found that when allowed to rest, the soln turns clear after a period of time.

 

anyway, leaving that in the flask on the heater overnight to evaporate the liquids, I notived what can only be described as "Glitter", like the stuff used on some Christmas cards or some makeup.

 

now as more liquid has evaporated the "glitter" isn`t.

it`s more like larger yellow crystals (and the remaining liquid has a strange TCP type smell also).

 

KI is a Clear crystal, so what the hell is this stuff?

 

has the Ethanol played any part in this reaction?

[Gilded]

Man, I hate it when the precipitate is or looks like something completely different you thought it was going to be. :S And in this particular case, it could have been anything from impure reagents to the beer bottle you used to heat the stuff in. But hey, KOH and tincture of iodine are pretty inexpensive so perhaps you should start a glitter-business.

[YT2095]

there were No contaminants, with the possible exception of Zinc contamination in the KOH (it would only be tiny though).

[ed84c]

The TCP smell will probably be iodine related. as for the 'glitter' K2CO3 is silver, and can be made from B(OH)2 so it is probably therefore a reaction with the C2H5OH

[YT2095]

there`s Boron involved?

[jdurg]

Was the glass borosillicate? With heating and the solvent properties of the solutions, there's a faint chance that some boron compounds could have leached out. Also, the yellow color of the ppt could be due to some iodine complexes forming. I know that a very dillute solution of iodine in water is actually a bit of a yellow color.

[YT2095]

it was conducted in a Pyrex boiling tube during titration, and later transfered to the 250ml erlinmeyer.

 

borsilicate they both are, I refuse to beleive that it had such an impact on nearly 2gm of crystal though!

 

the glass would have fallen apart! LOL

[ed84c]

Boron? sorry, it was a lazy attempt meant to signify a Benzene ring

[YT2095]

Benzene from Ethanol?

 

and you stated an OH (that would make it Phenol), how would I produce Benzene from Ethanol?

 

you`ve got my FULL attention.

[ed84c]

lol, no it was an example that K2CO3 can be made from a hydrocarbon such as that mentioned, so i thought mabye the ethanol did the same.

[raivo]

I can only say that KOH, I2 and KI will not make complexes with ethanol. Alternative examples are some bromides. ( MgBr2 * 6C2H5OH and LiBr * 4C2H5OH can be made by crystallisation. )

[YT2095]

the KOH has a higher probability of CO2 contamination than Zinc, so you Could well be right?

 

the problem is that there were alot of un-wanted ingredients in it, the Ethanol for a start, the water in KOH soln, there`s so many complex side reactions!!!

 

it could drive you nuts! )

[budullewraagh]

ok so just to get this straight:

 

you took tincture of iodine and added KOH until the solution turned clear.

you heated the solution and liquids boiled off.

 

perhaps you got some potassium ethoxide? i can't find its colour, but perhaps thats what you made. or maybe an iodine complex.

[YT2095]

the heat didn`t boil anything, it`s about 50c max in an erlinmeyer.

 

there`s still liquid left, it takes a good 2 days to evaporate the 50ml in there

[budullewraagh]

what do you think of the prospect of the ethoxide?

[YT2095]

distinctly possible, but organic chem is certainly not my stong point, and so I`ll need to do some further research.

 

it`s certainly a good avenue to explore though

[budullewraagh]

a-ha! sodium ethoxide is a white or yellowish hygroscopic powder according to the merck index. potassium ethoxide isn't mentioned but i think we have our answer. it is decomposed by water to the hydroxide and ethanol, but the alkaline solution should shift the equilibrium

[YT2095]

I`ve dissolved Sodium metal in pure Ethanol before, just ended up with a syrup type liquid that reacts quite interestingly with water, I never considered a Hydroxides action on ethanol though?

 

as I said Orgo is not really my area

[budullewraagh]

i'd say you have quite a high pH in that solution of yours. you evaporated a bunch of water and you had a good amount of hydroxide to begin with. potassium ethoxide is decomposed by water to form potassium hydroxide and ethanol. since you have so much KOH to begin with and a small amount of water, with a bunch of ethanol, you probably have potassium ethoxide, which does not decompose in ethanol

[YT2095]

the KOH soln is water based.

 

roughly 5gr to 100ml

[budullewraagh]

well, that's a 0.9M solution. with the alcohol there...and the hydroxide...i think it's safe ot say that there would be enough ethoxide to cause the colour change

[YT2095]

I just added 2ml extra kOH soln, the crystals remain the same color although the liquid is now perfectly clear again.

[budullewraagh]

well that makes sense, as the excess KOH shifts the equilibrium even more in the direction of synthesis of ethoxide

[YT2095]

ok....

 

so in a nutshell, am I going to get my KI eventualy?

 

or should I restart with my HI?

 

 

your call

[budullewraagh]

ah well.

 

you should get your KI, but it is of course very hygroscopic. if i were you i would remove the crystals formed and keep the evaporation going. with the crystals you have, i suggest you take a small sample and add a drop or two of conc sulfuric acid and see if you get HI gas. if you don't it's the ethoxide and it will burn. i suppose you could also try drying the crystals and see if they darken upon exposure to light and air.

try doing the latter first and with another sample try the former.