Heptylene
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Isopropyl iodide success!
This is a follow-up to the thread I started recently on making isopropyl iodide from iProH, red phosphorus and iodine. I obtained what I believe was a mixture of isopropanol
and isopropyl iodide which was difficult to separate either by distillation or by repeated washings with water.
Last time I used 2 eq. of alcohol compared to iodine. Today I ran an experiment on a 0.25 mol scale using only 1 eq. of alcohol.
The procedure is as follows:
To a 100 ml flask equiped with a reflux condenser and a stir bar there was added iodine (0.25 mol) and isopropanol (0.25 mol). The mixture was stirred
without complete dissolution of the iodine. There was then added at once the red phosphorus (0.092 mol, about 10 % excess of what is needed to make
phosphorus triiodide). The reaction heated up very rapidly and started boiling vigorously. White smoke started escaping the condenser. Those fumes
were tested w/ pH paper and found to be acidid. The mixture was cooled with a water bath and stirred for 30 minutes. Then all the volatiles were
removed. A single fraction came over at 78-80 °C: clear orange liquid.
The orange liquid was washed with aq. Na2S2O3 then with water (3x) and dried w/ Na2SO4. There was finally obtained 30.7 g (72 %) of clear colourless
liquid of density 1.68 g/ml (measured with a volumetric flask).
The literature boiling point of isopropyl iodide is 90 °C and its density is 1.70 g/ml, so this isn't too far off.
My big mistake was adding the red phosphorus all at once without proper cooling. This could easily have been worse if I had done this on a 1 molar
scale.
In conclusion the use of red phosphorus and iodine is suitable to make nearly pure isoproyl iodide provided you don't use an excess of alcohol.
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lowtech
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nice work
these reactions with red P are quite wild when you dump it all at once, on larger scale ending with nasty runaway.
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DavidJR
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What form does the phosphorous end up in once you're done?
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Swinfi2
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Somebody let me know if I'm wrong but I believe phosphorus used with halogens has extreme affinity for water and is turned onto phosphoric acid.
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Heptylene
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@DavidJR apparently the product is phosphorous acid: H3PO3, although I haven't really tried to verify this. What's left of the reaction dissolves
readily in water, except for some excess red P which remains. Btw the leftover phosphorus can be recycled by washing with water or ethanol and drying.
@Swinfi2: Indeed phosphorus halides PX3 react with water AFAIK to form the acid HX and phosphorous acid H3PO3. Therefore it is important to work with
dry starting materials. The alcohol is trivial to dry, but iodine is more tricky. For this reason I started from commercial iodine (ebay) as I
couldn't efficiently dry the one I made from KI.
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Chemi Pharma
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At really, PI3 hydrolyses to HI and H3PO2 (hypophosphorous acid). The HI decomposes into H2 and I2. The H3PO2 reacts with the remained I2 to
regenerate HI again and H3PO3 (phosphorous acid). This is the mainstream of this reaction. At final you will have the alkyl halide, H3PO3 and water.
Then, is enough do a simple destillation, neutralize the free iodine distilled with thiosulphate and dry with anhydrous magnesium or sodium sulphate.
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VSEPR_VOID
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I did this a few days ago with:
10g of 99% ISPA
25g of I2
10g of rP
I recovered 7g of the rP.
I added the rP slowly and with cooling (kept bellow 80 C)
My product was clear and had the correct bp and density. When mixed with water it slowly turned yellow-orange
Within cells interlinked
Within cells interlinked
Within cells interlinked
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