It gives even me the creeps at the thought of working with it. Its actually the weakest of the hydrohalic acids, excluding oxyacids, but of those composed of just hydrogen and a halogen, HF is the weakest, they get stronger going down from chlorine, bromine and iodine. Hypothetically hydroastatic acid (from astatine) and IF it behaves like a halogen, the superheavy element tennesine, hydrotennesic acid would be the strongest, although it may behave closer to a noble gas more similar to argon, krypton, neon, xenon etc. It and astatine though are extremely radioactive, the half-life of astatines longest lived isotope is only a little over 8 hours, and a visible sample would emit so much radiation as to instantly vaporize itself. Its never actually been seen in solid form. Creating enough to try and cool a sample down has never been done, only micrograms or maybe milligrams have ever been made at any one time. So hydroiodic acid is the strongest of the common hydrohalic acids, not deadly poison like HF, but its a damn strong acid, and it'll eat holes in a steel lab clamp-stand block from just a drop or two. Also a strong reducing agent, particularly when combined (and I bet breaking bad wouldn't leave this out) with red phosphorus (it creates phosphorus triiodide, which although unstable and not storable as a purified reagent, can be prepared and used in-situ, the PI3 iodinating the substrate then the HI reducing the iodide usually to a saturated alkane, the PI3 hydrolyzing as it does so, and making itself available to more HI in a catalytic cycle. Its a harsh set of conditions, though and not suitable for delicate substrates of many kinds. But its a well known reaction, chemists AFAIK often resorted to it as the reducing agent version of pounding their substrates with a sledgehammer and its also used in making meth, although the Birch-Benkeser reduction (lithium metal in anhydrous ammonia, or, a more recent innovation that for performing a Birch on anything, since this way you need no dry ice to liquefy anhydrous ammonia, is to generate the ammonia using calcium oxide (quicklime, a powerful dessicant and fairly strong base) mixed with an ammonium salt such as sulfate or phosphate, adding just a ml or so of water to get it started giving off NH3, the trick is, that the quicklime doesn't release water during the rxn, and itself dries your ammonia, so you can even get away with it without a drying tube, and just leading through a pre-cooling condenser, then through into your flask, purged with argon, and filled with dry diethyl ether, the flask being sat in a bath of iice, salted with calcium chloride and table salt, and the delivery tube being situated right at the bottom, so as to bubble a constant stream of anhydrous ammonia through the ether, but as a gas, without having to liquefy it using dry ice condensors in a dry ice-acetone bath. That way you just have to continuously bubble the NH3 through the ether with a stirred suspension of fine lithium metal chips and curls, shavings etc so as to contact the lithium, in fine little bits as best as possible. It avoids ever having to handle the rather dangerous anhydrous ammonia in its condensed cryogenic liquid form, and is a lot sater. Although it takes a lot more ammonia gas to preform your solvated electron mixture, which at first, done in-situ this way turns greenish blue, but then does go deep dark midnight blackish-blue, indicating a solution of solvated electrons, Which then will reduce your substrate, added as a paste, or thick slurry, dampened with a little alcohol to serve as a proton source.
It does work for Birch reductions of compounds, although one has to calculate the total quantity of Li needed generally, rather than adding it to liquefied anhydrous NH3 and adding substrate to be reduced first, then slowly adding lithium chips until the blue of solvated electrons no longer disappears, upon which you know your substrate has been reduced since its no longer causing the loss of blue color to white.
