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Topic: Quat. Halide Reaction/Color Change w/Organic Alcohol  (Read 504 times)

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Offline chrslmx

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Quat. Halide Reaction/Color Change w/Organic Alcohol
« on: October 26, 2020, 04:57:52 PM »

This is my first post, I'm hoping the chemistry experts here can give me some guidance.

I observed an unexpected color change dissolving a quaternary ammonium iodide in alcohol. 

I dissolved 1.5 grams of tetrabutylammonium iodide powder in about 8 mL of water-white 2-ethylhexanol (2EH) at room temperature.  TBA iodide is a white powder, which forms a clear colorless solution in water and methanol.  Immediately upon adding the 2EH, the solution began to turn yellow-brown.  Within a minute of swirling, the TBA iodide appeared to fully dissolve or react to form a dark brown solution free from residual solids or haze.

The reagents are somewhat old.  The TBA-I is about 2 years old, the 2EH is about 6 years old.  However the degree of opacity is so significant I find it hard to believe that impurities alone are to blame.  My instinct is that molecular iodine is somehow forming, but I am having difficulty identifying a mechanism that occurs so rapidly.

I do not have newer reagents to determine if it is a purity issue.  Any help would be appreciated.

Offline wildfyr

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Re: Quat. Halide Reaction/Color Change w/Organic Alcohol
« Reply #1 on: October 27, 2020, 04:12:23 PM »
I agree elemental iodine is forming

Here's what I think. Elemental iodine is insoluble in water. You have tiny amounts of iodine that formed naturally over time in your TBAI (happens to virtually all iodide salts with age). When you add it water, the quat salt dissolves, but the iodine doesn't. However when the much more greasy ethylhexanol hits the solution, those minute iodine crystals dissolve and the solution changes color.

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