VSEPR_VOID
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Isopropyl Iodide Synthesis Aluminium Iodide Catalyst Results
The Mystery of the Diapering Iodide
A rbf was charged with 25g of I2, 20g of 99% isopropyl alcohol, and 60 mL of water. The flask mixture was stirred and a condenser and thermometer
added to the flask. Slowly, 2g of powder aluminium (grey) was added. The temperature did not change. The solution was dark purple.
[Special Note: Previously the same reaction was attempted with no water. This resulted in a run away reaction between the Al and I2 that resulted in
the flask boiling dry.]
Slowly again, the flask was heated. A reaction started and the temperature rose sharply. A yellow liquid was seen condensing. The flask was moved from
the hotplate and into a ice bath. Once cooled to 50 C, the flask was once again heated. The flask was refluxed at 90 C without indecent.
At an hour and a half the liquid changed from dark purple, to yellow, and finally to an off-white clearish grey. It is important to note that during
reflux no I2 vapors were seen the escape the condenser or leave the flask.
The rbf was left at room temperature for an hour and no layers were seen to form. The solution was removed from the flask and transferred to a beaker.
400 mL of water were added. The solution, now a very light yellow, was made saturated with NaCl. No layers formed. This saline mystery solution was
distilled. Bellow 100 C a light yellow distillate was collected with a density of 0.8g/mL.
The desired product should have separated either in the original reaction flask, or when added to pure water, to form a separate layer. When distilled
it should have had a density of greater than water.
Where did the iodide go? It has not reacted with the ISPA, there is not enough aluminium to react with it completely, and it did not escape the flask.
Has anyone had any luck preparing isopropyl iodide using an aluminium iodide catalyst?
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Chemi Pharma
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@VSEPR_VOID, remember what @AVBayer said in another thread about ethyl iodide. That's theorical:
"Saturated primary (eg ethanol) and secondary alcohols (eg isopropanol) are unaffected by aluminum triodide. Allylic, benzylic, and tertiary alcohols
are regioselectively converted to the corresponding iodide by the reagent. There is little expectation that ethyl iodide will be formed with aluminium
triodide, at least in any useful amount."
http://www.sciencemadness.org/talk/viewthread.php?tid=2727&a...
You didn't produce any isopropyl iodide at all in your experiment and you have distilled only an azeotrope of water and unreacted isopropyl alcohol.
That's the reason you didn't get two imiscible phases as result.
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unionised
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Interesting notion.
Anyway...
My best guess about the iodide is that it's either still in the flask or was lost as HI.
Water will destroy isopropyl iodide fairly quickly.
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VSEPR_VOID
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If it formed HI then it should have gone on to react with ISPA. Water does not hamper the reaction if there is HI.
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unionised
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This sort of thing strongly suggests that it would hydrolyse
https://qualifications.pearson.com/content/dam/pdf/A%20Level...
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VSEPR_VOID
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The literature (Vogals Practical) calls for ~50% HI. The equilibrium favors ISPI. But I guess I could try it with another solvent. Either more ISPA or
ether.
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VSEPR_VOID
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I preformed the reaction with elemental phosphorus as a catalyst and got a product that was not miscible in water. I am still wondering what happened
to the iodine in the original reaction.
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Chemi Pharma
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@VSEPR_VOID, I did a research and found the source of AvBaeyer assertion when he say:
"Saturated primary (eg ethanol) and secondary alcohols (eg isopropanol) are unaffected by aluminum triodide. Allylic, benzylic, and tertiary alcohols
are regioselectively converted to the corresponding iodide by the reagent."
This was extract from:
Regioselective transformation of allylic, benzylic and tertiary alcohols into the corresponding iodides with aluminium triiodide:
deoxygenation of vicinal diols
Parijat Sarmah, Nabin C. Barua
Tetrahedron,Volume 45, Issue 11, 1989, Pages 3569-3574
https://doi.org/10.1016/S0040-4020(01)81035-8
I think @unionised is right when he say that the iodide was lost as HI. Seems like AlI3 doesn't hydrolyse at a rate fast enough to permit a high
concentration of HI to be able to drive the reaction onto the formation of the alkyl iodide, like PI3 does, and evaporate from the solution first or
remains unchanged in the solution until destillation.
It's important to remember that PI3 hydrolyses producing HI and H3PO2, and the last continuous regenerate the I2 from HI that decomposes, turning it
back to HI, increasing it's concentration in the solution. The same doesn't occurs with AlI3.
Would be interesting analyze if the distillate contains an azeotrope of water and isopropyl alcohol and an azeotrope of HI and water either, or even
iodinated water. This could explain your question about where the iodine has gone.
[Edited on 30-7-2018 by Chemi Pharma]
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VSEPR_VOID
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I got rid if the reaction mixture. I could have added some H2O2 to see if you are right.
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