I've been delving into the subject of the mechanism of generating HI, and it seems to me that one should make a lot of effort to recover it with a minimum of steps (steps being sites of mechanical losses and operator error).
When the e/rp/i reaction is done, a lot of HI is generated, and one of the classic signs of a good reaction is that at the end the HI solution is still concentrated HI, almost clear maybe a faint tint of yellow. It seems crazy to me to go and bind up that HI with a base (NaOH presumably) meaning you have to unhook it again later on if you want to re-use it.
So, in our post reaction solution we have a lot of phosphoric acid, hydriodic acid and methamphetamine, which is likely going to be bound up with a proportion of HI and H3O4P as is found in the solution. we would have also some water in the solution. The water and HI would distill straight out of the reaction mixture, so long as the temperature was controlled so as to prevent phosphoric acid from vapourising and coming across as well (below 150 degrees) though obviously, this is an inert element in the reaction, it would be nicer to leave it out, feed it to your flowers
the meth obviously can't boil out below the temperature of the dissociation of its salts with HI and phosphoric acid... a lot of people say to boil your post reaction liquid, i say, distill it. Thinking about what would be needed to do this, it's not much either, a metre of vinyl hosing attached to the top of a small flask (the rxn flask probably) with a thermometer to monitor the temperature that is distilling across, and the end dripping into a receiving container (preferably the storage container) - oh and probably good to either blow air over the tube or make it coil through a bunch of water or something similar. Vinyl tubing of about 1m length with fairly high boiling liquids condense vapour effectively enough to be practical. People use vinyl hose all the time with push-pull setups so it must be safe enough to use with boiling HI and water going through it (i was rather surprised to find that i was able to distill a light fatty acid in a vinyl tube... the only things which damage vinyl seem to be boiling aromatics, and probably ketones, aliphatics are fairly benign at below about 80 degrees.)
Then once the temperature in the boiling flask with rxn mixture starts to rise above 127 degrees or not distilling anything anymore or looks almost fully dry, the majority of the HI will be recovered. A pinch of the rp recovered could be added to the container the HI is stored in to keep it as 57% HI until next time
and subsequent reactions done as HI/rP reactions rather than I2/rP reactions. Saves all that work turning the iodides back into iodine.
HI reactions are much safer to start than I2/rP based reactions because the reaction starts immediately that the ephedrine is added and flask fires are much easier to avoid because the reaction takes place immediately and doesn't need to be prompted with heating. The rP only reacts in a HI/rP reaction when the HI reacts and decomposes into I2 again, so one doesn't need to risk raising the temperature high, as once the ephedrine reduction starts taking place (which just requires enough joules of heat energy to kick off) in an already formed solution of HI, the temperature is already high enough for the rP to continue turning the I2 into HI.
If one had nice little pieces of ground glass thingies, still heads and whatnot, one would take the condenser off the top of the flask and replace it with a still head and attach the condenser to that.. and voila. Then the meth phosphate and red phosphorous solids remaining would be dissolved, gently boiled to clarify and rP filtered and the meth acid/base extracted into the HCl salt.
Obviously it is most important not to let the temperature get high enough to start the remaining phosphorous burning, this should be fine, i think this requires fully dry rp and over 130 degrees to occur so it's probably wise to stop distilling the HI off at the point there is almost no liquid left in the reaction mixture, just shy of fully distilling it as that red phosphorous is nasty, and the whole point of distilling the HI without first diluting it is so that it remains concentrated enough to react later on.
