I have some iodine tincture containing 2% iodine, 1% KI and 74% isopropyl alcohol. I assume the other 23% is water. Anyhow, I added KOH flakes into
the solution and stirred until all KOH appeared dissolved. I added a large excess of KOH but no colour change occured, meaning no I2 got converted
into KI. I added about 15mL of distilled water and the solution rapidly turned clear. I don't understand why the reaction didn't occur before I added
the distilled water. chemrox - 25-4-2012 at 14:20
K-isopropoxide
Alcohols mixing with metal hydroxides form alkoxides. Both parts ionize. The alkoxide ion; ethoxide, isoporoxide, etc. associate with the metal ion.
The association is rather stronger than with metal ions in water so the behavior is different.
[Edited on 25-4-2012 by chemrox]mycotheologist - 25-4-2012 at 14:35
You've lost me. I thought only elemental potassium could produce isopropoxide. I assumed that a secondary alcohol is even harder to convert into an
alkoxide due to the alkyl groups destabilising the alkoxide anion. Also, wouldn't K-isopropoxide reduce the I2 the same way KOH does?
[Edited on 25-4-2012 by mycotheologist]chemrox - 25-4-2012 at 15:16
No I once thought that too and ran into this in syn fuel applications. There is an equilibrium but the more KOH you dump in the more it shifts toward
alkoxide formation. So yeah, you've got a mix ... but the alkoxide might be ruling the roost so to speak because of the quantity of KOH. (I'm
ducking by the way, this is NOT my area and somebody like nicodem is sure to flame my ass)mycotheologist - 26-4-2012 at 10:42
Thats pretty interesting, I want to isolate some solid isopropoxide now. Is KOH a stronger base than NaOH? Well, what I'm really asking is if this
only occurs with KOH, and not NaOH.
BTW yesterday after adding the water and observing the whole murky brown, mixture turn to a clear, slightly yellow solution, I tested the pH and
noticed it was really high. I kept adding tincture (ended up adding the whole 500mL bottle I had) until the pH became neutral. I still don't get why
the K-isopropoxide didn't reduce the I2. Is it because it can only dissociate into ions in water, not IPA?simba - 27-4-2012 at 10:27
