03-01-04 19:43
No 492183
First, I wanted to thank Argox for the great write-up on the production of hydriodic acid from potassium iodide. I found the reaction worked almost exactly as described, with the hydrogen sulphide gas coming over at first before the real juices start flowing. The only complication, which I found to be quite annoying, was the constant suck-back of the water trap into the receiving vessel during the reaction. I am going to experiment with a couple polypropylene check valves to see if I can solve that one.
The problem is that the product is cosmetically unappealing to several uneducated individuals, who are insisting that the liquid must be yellow, not dark brown. Argox suggested boiling the product with a little red phosphorus and then using a reducing agent such as hypophosphorous acid to stabilize. I noted that hypophosphorous acid in itself is a list I chemical that I would like to avoid ordering, although I already have access to red P.
So, has anyone tried using an easier to obtain chemical than hypophosphorous acid as a stabilizer? What are the general ratios used?
I have UTFSE on this one but I seem only be able to pull up the argox recipe. Thanks.
(Hive Addict)
03-01-04 19:59
No 492189
I have made HI this way several times and it is always a very dark red color. Nevertheless it works for its intended purpose. It only takes a few drops of hypo to clear the red up. After adding about 5% hypo to the solution within 5 minutes it will bee clear like water. If you don't have hypo just use rp in the rxn and it will work fine. However i don't know if it can bee used to stabilize it. How long were you wanting to keep it? Hopefully not long.
Heres some links to some of my old post on this subject:
Post 438386 (SHORTY: "Hi from KI", Stimulants)
Post 468969 (SHORTY: "I didn't need to redistill.", Stimulants)
It wasn't Me!
(Hive Bee)
03-02-04 02:07
No 492274
Swix cant comment quantitatively on the ratios (as he doesn't know); but hypo, Phos acid and redP can all be used to 'clear' HI made from KI and H3PO4.
Hypo will do it at room temp with only a few drops required, Phos Acid and RedP require greater time, ammounts and the addition of heat.
As a rough ratio, Swix will chuck in maybe 2g of Phos Acid solids to 50mL of red 57% HI; then boil for 5 mins to clearness. Swix doesn't know how long it would keep like that, as it is always used in a reaction almost immediately - to minimise decomposition and lowering of concentration.
If storing for long periods, it makes sense to use an agressive HI recycler like Hypo. Lab grade HI uses Hypo as the stabiliser as well.
As a side, Swix had a little leftover yellow/red 57% HI that he put a a little sealed bottle in the dark at room temp. It was reopened a few weeks later and it had gone an even darker red colour and wasn't fuming at all (indicating decomposition). He didn't bother to weigh it (to determine conc.) as it was to be discarded into his mouth for dinner - but he was sure that it would of dropped below the 57% it started at. Food for thought.
yummy
(Hive Bee)
03-02-04 10:24
No 492369
(Rated as: excellent)
Some time ago I purchased a solution of 57% HI from a chemical supplier. It was colourless when bought, but quickly discoloured to the dark red-brown described above. The iodide ion, I-, is colourless, but HI acts as a reducing agent by itself being oxidised to iodine, I2, which has a rather distinct colour. With pure HI as starting material, iodine will be the source of any coloured impurities.
The same phenomenon occurs with alkyl iodides; the ethyl iodide I have has also taken on a brownish colour. Alkyl iodides are often stabilised by the addition of metals such as copper or silver, which seem to inhibit iodine formation. Unfortunately I can find no references for this working in the presence of a strong acid such as HI, as adding metals to acids generally results in the production of hydrogen and a metal halide:
2 HI + M __> H2 + MI2 (where M is a generic transition metal such as Cu or Ag)
From a chemical perspective, there is no point in removing the colour, except maybe to inhibit any potential side reactions from the action of iodine on (pseudo)ephedrine. The initial dark HI solution I had was used in an HI/P reduction, giving a 76% yield of product after a 36 hour reflux (see the final step of Post 475219 (Kinetic: "Benzene -> methaephetamine", Novel Discourse)). Very quickly on heating, the phosphorus present reduced the iodine back to iodide, making the reaction beautifully colourless for its entirety.
If you want to reduce any iodine present to colourless iodide simply to keep others happy, a literature search for suitable reducing agents indicates that formic acid, among other reagents, is suitable. The ancient reference given is Monatsh. Chem.; Vol. 25; (1904); 591 - 591, a journal I don't have access to. The reaction is simply:
I2 + HCOOH __> 2 HI + CO2
Since the only byproduct from this reduction is carbon dioxide, there should be no problem with interference in the subsequent reduction of (pseudo)ephedrine.
Other reagents that should keep HI colourless are phosphine, sulfur dioxide, red phosphorus, phosphorous acid and hypophosphorous acid. Although some may require heating to actually remove any colour, the formation of coloured iodine is relatively slow, so all of these reagents should supress the reformation of iodine from HI. As a guide, the chemical suppliers Lancaster stabilise their HI with 1.5% hypophosphorous acid.
After finding the reference about the use of formic acid to produce HI from iodine, I couldn't help but wonder if it could be a viable alternative to red phosphorus/phosphorous acid/hypophosphorous acid as a recycling agent in the HI reduction. I can't see any way in which it could hinder the reduction. Maybe someone could give it a try.