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Author: Subject: Is isopropyl alcohol bad at solvating hydroxide ions
mycotheologist
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[*] posted on 25-4-2012 at 14:14
Is isopropyl alcohol bad at solvating hydroxide ions


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.
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chemrox
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[*] posted on 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]




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mycotheologist
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[*] posted on 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]
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chemrox
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[*] posted on 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)



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mycotheologist
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[*] posted on 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?
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simba
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[*] posted on 27-4-2012 at 10:27


Quote: Originally posted by chemrox  
(I'm ducking by the way, this is NOT my area and somebody like nicodem is sure to flame my ass)


hahaha that really made laugh
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smuv
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[*] posted on 29-4-2012 at 23:24


Under these conditions, you probably made iodoform. Add xs water, yellow precip?



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