HI/P Reduction of Ephedrine-Exothermic?

[katsogiannos]

SWIM has a question relating to HI/P Reduction of Ephedrine.

If the reactants are refluxed under vacuum, will the reaction be less exothermic, than if tap water or ice water is run through the condenser?

Will it make a difference at all?

[Rhodium]

If you try to perform it under vacuum, you are going to suck out any formed free hydrogen iodide from your flask. Not good. Also, the temperature itself is what keeps the reaction going at a reasonable rate, and with the use of vacuum you are going to lower the reflux temperature.

[MnkyBoy78]

THe only in which one could us a vacume is if the rxn vessel is to be sealed.  (ie Not using a condensor or ballon).  Add two of the main components (I and E), evacuate the vessel, remove vac hose without releasing the vacume.  Inject the remaining item (Hypo is easiest here).  THe only thing accomplished though is the removal of the atmospheric gasses that are in the vessil apon sealing.

All in all, the chief is right.

[SHORTY]

MnkyBoy78,
I remember you mentioning this before and have been meaning to ask you for some details.  For example:

What size flask do you use and what is the maximum amount used in that flask?

Is it necessary to anchor the stopper in place with tape or some other way?

Is the flask sealed for the duration of the rxn and is external heat used?

[MnkyBoy78]

[spectralshift]

It'll cause it to boil at a lower boiling point, and that will slow the reaction down like Rh says.

sealed reactions are for dummies, the same can bee acheived with a Push/Pull apparatus.
There's so many thing's that could be done with that to change pressure required to move the fluid, not just larger amounts of fluid...

Is there a critical reflux temperature in this rxn where ephedrine starts decomposing or otherwise takes damage?

There's some documents I downloaded regarding pressurized HI/P reactions in industry, Ill probably find something in there.

[biotechdude]

When one performs sealed reactions with a flask-condenser-balloon setup; HI(g) fills the balloon and causes it to expand.  However, sometimes the balloon expands too much (risking popping), so one can pinch off the big balloon, and put another one on.  This second (or third etc) balloon will inflate then deflates entirely as the rxn proceeds; at this point the inflated 'reserve' balloons are reattached until they are deflated and so on.

Is there anything wrong with this practise?  Swix thinks it is of double benefit as the dangers of sealed reactions are nullified; and the conc. of HI in solution is kept at an optimal +57%.  The only skill is in removing and reattaching the balloons without mushroom-clouding the room with HI(g).  Two sets of hands makes this much easier...

[SHORTY]

Why not use a bigger balloon and if its not thick enough then put one inside the other.  Then you wouldn't have to worry about getting a face full of HI if you lose your grip on the balloon or if it pops in your face.

I have had both happen to me and thats why i use 2 big balloons and leave them on for the entire rxn.