Argox's high volume hydriodic acid production method is an efficient, easy, and cost effective way of producing large amounts of acid. However, even with my many dreams and thorough understanding of the procedure, there is still some weaknesses that I have yet to overcome.
For those not familiar with the method, please read:
Post 271993
(Argox: "Hydriodic Acid--Step by Step Write-Up", Stimulants)The reaction works pretty much as he describes, with a small amount of a milky substance identified as hydrogen sulphide distilling off before the aqueous HI starts flowing. The hydrogen sulphide needs to be carefully removed and neutralized with a weak lye solution, and this all must be performed in the confines of a fume hood.
I did not dream of the violent bumping that Argox described, and instead have found the reaction to proceed quite fine without the need for stirring.
The water trap suck back that he describes is constant and anoying. A simple plastic tee fitting with two teflon or polypropylene check valves solves this nuisance, with one valve allowing air to be sucked in from the open air during a suck back, while the other valve allowing HI gas to be pushed into the water trap, but preventing the suck back of the water trap into the receiving flask.
It is very important to use as much heat as possible during the reaction, as MOST of the HI produced is at a very very high temperature. The initial acid that comes over in distillation is quite weak, but the longer and hotter the reaction goes, the stronger and stronger the acid becomes. We continually dream acid with specific gravity of 1.82 - 1.9, which is considerably more than the azeotrope of 1.72. Rather than diluting, when used as is, we have found exceptionally improved yields in the RP/HI reaction. 75% w/w is not at all uncommon and is expected with super strength acid. However, this acid fumes like nothing you have ever seen, and should be kept in a sealed container and in a freezer before use.
75% Phosphoric acid should be used with the reaction, in equal weight to the Potassium Iodide, if the super strength acid is desired. The water trap will have weak acid, but it can be reused in subsequent batches or used to dilute the super strength acid in the receiving flask down to something you are more comfortable with.
I have also found that the concrete residue that is left over can be removed easier if it is refluxed with some phosphoric acid, after the reaction is over and cooled of course.
Here is the problem I am yet to overcome: No matter what we do, the boiling flask always develops cracks, most likely due to the extreme temperatures required for this reaction. No matter how slowly the reaction is allowed to cool, with only slight reductions in temperature over several hours, the vessels still crack. We have also found that using a lower power setting on the varistat results in a poorer yield, but cracking still occurs.
Has anyone had any success with using materials other than glass? The glassware guy that made this said that this is the best glass for the job. Teflon is not an option because the reaction temperature is too high. Quartz has been suggested but I have no experience with this.
I am wondering if some type of ceramic vessel can be constructed, but is ceramic compatible with strong acids?