Author Topic: excess rP  (Read 2778 times)

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  • Guest
excess rP
« on: April 01, 2004, 07:52:00 AM »
what happens if there is excess rP in a reaction? does it continue to react with the I2 for as long as it reappears in the reaction, or is there some problem with doing this? Assuming that the correct amount of water is in the reaction to hold the HI that forms from the present iodine...


  • Guest
Excess RP don't hurt
« Reply #1 on: April 01, 2004, 09:16:00 AM »

does it continue to react with the I2 for as long as it reappears in the reaction, or is there some problem with doing this?

Although, swim is far from an expert on this, in his reactions when he has used too much RP, this seems to be exactly what happens.

As far as swim knows excess RP, doesn't hurt a reaction. (Swim is talking a few grams) In fact swim likes to use what most would consider excess MBRP, if it has been run before.  If it is it's first run, though one can cut back to .60RP:1 E. 

As Geez and Jacked  both pointed out the ratio of RP should be in relation to the I2 rather than E.


  • Guest
« Reply #2 on: April 01, 2004, 09:21:00 AM »
yeah i thought that might be the case.

actually i've come to the conclusion the main important ratio for a good reaction is the right amount of water per amount of iodine, since the reaction proceeds via the formation of concentrated HI. The number of total moles (including re-reacting with I2 formed in the reaction) of HI that can be formed is limited by the amount of red phosphorous, and this limits the amount of ephedrine which can be reacted (equimolar to the I2)

Incidentally, those screw-down garlic presses made of plastic squash filters full of I2 crystals to almost dryness... highly recommended for those without cold fingers  ;)


  • Guest
« Reply #3 on: April 01, 2004, 10:01:00 AM »
"As Geez and Jacked  both pointed out the ratio of RP should be in relation to the I2 rather than E"

thats defenately correct in my point of view.
since RP is needed for the HI than must be related to I. HI in a whole is what should be related to the E...


  • Guest
enough red phos
« Reply #4 on: April 01, 2004, 02:08:00 PM »
As long as you have "enough" red phosphorous in the flask to react with the I2 you add, the amount of HI produced will be determined by the iodine available. Red phosphorous is consumed in this reaction. A little over a third of a gram of red phosphorous is consumed in a long wet reflux for every gram of pseudoephedrine that is reduced to meth. As long as you have that much or more red phosphorous in the flask, you have enough red phosphorous for the reaction to complete, and red phosphorous is the limiter of how much HI is produced.
Most of us add more than enough red phosphorous to the reaction knowing that what is not needed by the reaction will not be consumed by the reaction, and will be available for later reactions. An excess of red phosphorous is added to compensate for impurities and contaminants in the red phosphorous, or as a hedge against them.  

Having an excess of red phosphorous in the flask can be a problem at the outset, when the red phosphorus and iodine react to make HI.  If there is an excess of red phosphorous present the production of HI will take place faster and more heat and smoke will be generated by the reaction than would be the case if a molar amount of red phos were added. This part of the reaction is a prime point for byproduct formation, particularly in dryer reactions. This result is avoided by making the HI first, then adding the pseudo. It is not routinely a problem in reactions that are wet at the outset, such as the start of a long wet reflux. It is less of a problem when only a molar amount of red phosphorous is present at the start. After the initial production of HI, the presence of an excess of red phosphorous does not appear to be detrimental.


  • Guest
Excellence Defined...
« Reply #5 on: April 01, 2004, 04:28:00 PM »
As usual Geez!
Many factors come into play that aren't routinely observed or easily explained.
Geez's summary above touched on many of those issues.
As I was reading down through this thread, it brought to mind a statement that Geez made in the "hypo thread"?? that described Ibee's inclination to use less dh2o in the LWR than SWIG and Ibee uses more RP than SWIG.
Since Ibee always starts wet when mixing ingredients, the concerns of excess RP aren't the same as one would have if doing a dry rxn.
Having the highest HI concentration possible throughout the rxn is the main factor that determines complete reduction.
If the impurity producing mechanisms could be pinpointed, it would be easier to determine the ideal conditions that affect their removal or conversion.
With safeguards in place such as sufficient hydration throughout the rxn, excess RP is seen to balance the equation some and in Ibee's Eyes, it's seen as a benefit.
After all, the rxn will only consume as much RP as needed, so the remainder will be recoverable as well as a tad cleaner having undergone some extra scrubbing and conditioning toward it's next exposure to that environment.
(Provided it wasn't tainted or contaminated with gaak from unclean pfed)
If the dh2o ratio is overshot at any time and thereby weakening HI concentration during rxn, Excess RP could be thought of as a cushion to this condition provided the I2 ratio is suffient to keep the HI concentration constant on the High %age side.
The way Ibee looks at impurity creation/transition/conversion/elimination is this:
One must assume that the consumed(used) phosphorous in rxn has to go someware. The various changing states or gasphase changes taking place may play a larger role than suspected in dealing with the multitude of impurities created.
Just like Iodosides and the like.
But most of the I2 is recoverable. If it's not left attached to ephedrine or meth by prematurely pulling the rxn.
Ibee's point is this:
In a 10g rxn, ~3g of RP gets used and some of that must attach to something someware as it's not recoverable...Pooof! Gone!
Maybe it's phosphine, phosgene, or whatever phos gases that assist in these impurity transformations. Who knows?
But if they are responsible in some impurity creation, Ibee feels that allowing these side rxn to fully mature, run their course, and complete in rxn it might account for less of them beeing present in a product where the rxn wasn't running at it's fullest concentration.
Therefore Ibee looks at excess RP as a buffer or a cushion in assuring ideal HI concentration and recycling.
Now that I've left everyone as confused a me...
I feel better now! :)
While I've put much thought into this, it's not as easily described as I'd like but I think someone might get my drift on ware I wanted to GO with this!
Hey...I try ;)


  • Guest
« Reply #6 on: April 01, 2004, 06:33:00 PM »
as far as i can tell it's not strictly correct to call the ratios ratios in a reaction sense. all the I2 reacts to form all the HI it can form at once. The phosphorous reacts with I2 that reforms from the iodoephedrine reduction. This is two distinct reactions systems taking place simultaneously. it's more like a pipeline, rp + I2 in, HI out; and a second pipeline HI + E in, I2 + meth out (with the intermediate stage with iodoephedrine) The second pipeline depends on the first pipeline being full at all times, as this creates the conditions for maximum concentration of HI possible with the available I2 source.

anyway the point i was trying to make is if one uses less iodine one needs to also use less water because the total mass of hydriodic acid in the solution only reaches the maximum determined by the number of moles of HI that form, and so one is always aiming to shoot slightly short of that, and it seems to me the funny little yellowish crystals that form in the condenser are there to tell you to add a drop or ten more of water. When the crystals are there but almost not, the reaction is going to prduce optimal HI concentrations.

The only limiting factor i can see is there would be a temperature window in which the reaction can take place, and pending the number of joules in the reaction per period of time, one gets a resultant rate of regeneration of HI out of the reaction according to this rate. The HI takes a certain amount of time per joule per watt of heat to generate, and the HI reacts with another set of reaction kinetics. These formulas, if calculated for the range of temperatures the reaction can run  at and tlc'ed to in testing to monitor the ratios reaction products to verify that the numbers match the real world scenario.

so anyway, the point of all this is that i propose a set of cascading limiting factors which flows like this:

1: the amount of water is determined by the amount of expected HI formed in the reaction. one wants to aim for about the right amount to form the right concentration. the formation of the crystals in the condenser indicates a too dry reaction, it indicates that HI is beyond the saturation. One wants it a little on the saturated side, i think the target should be a small amount of the crystals are formed but very little. If one needs to wash it down every 8 hours that means that water is being lost from the reaction.

2: The amount of HI, in total, that could ever be formed in the reaction, is limited by the amount of the HI generator, in this case we mean rP. Each mole of rP can produce 'x' moles of HI from a cumulative total of 'y'. The way i see it, the phosphorous just sits there and waits until it bumps into some iodine, which also forms at the end of the reduction of some ephedrine.

3:The ratio of HI to ephedrine is of some importance too, the HI will react randomly with possible reactants in a roughly statistical manner - that is, in the beginning of the reaction, iodoephedrine is formed, and as the reaction proceeds, some of the iodoephedrine is reduced as new iodoephedrine is formed, and once that happens I2 is released back into the reaction in (2). Clearly there would be a fairly wide margin for error with regards to the total amount of HI in the reaction versus how much ephedrine it's going to chew through. Too much ephedrine for too small a quantity of HI occurs when the amount of iodoephedrine that could at the time in the reaction when it's reacting is such that all the iodine has been bound up in the iodoephedrine. This might be somewhat ameliorated if iodoephedrine has a greater reducability than ephedrine (which it probably does).

I don't know how to calculate all these things but i understand that all of these factors come into play. The reaction conditions are clearly very flexible and this accounts for the seeming disparity of 'ratios' in published methods.


  • Guest
No mention of phosphoric acid...
« Reply #7 on: April 02, 2004, 03:43:00 AM »
I have a somewhat different theory as i think that phosphoric acid forms as the rxn progresses and if allowed to react until all the rp is gone the end result would bee phosphoric acid.

This is because rp releases hypophosphorous, phosphorous and phosphoric acid at a very slow rate.  The hypo will become phosphorous which will become phosphoric.  All this is happening simultaneously during the rxn.

This is why hypo rxn's are so much faster than rp rxns.  If you continue to react a hypo rxn it will eventually stop producing HI and the solution is very much like phosphoric acid although i have no way of testing it.  Other than one time i added iodine to this solution and it wouldn't dissolve.  The same thing happens when you add iodine to phosphoric acid even with heat it won't dissolve.


  • Guest
Concentration of HI/Reaction Vessel
« Reply #8 on: April 02, 2004, 10:39:00 PM »
Not EXACTLY on topic, but along the same lines...SWIM usually does between 10-20g runs in a 500ml flask w/condom attached, as that was all she had available.  She started to wonder, though, if a smaller flask would provide a higher concentration of HI, and would this possibly make a difference in the end product?  Her reactions are currently running (wet) 12-20 hours.  Thanks!


  • Guest
flask size would probably have a negligible...
« Reply #9 on: April 03, 2004, 01:13:00 AM »
flask size would probably have a negligible effect on acid concentration.  The amount of water and reactants would determine the acid conc.


  • Guest
Thanks, Foxy!
« Reply #10 on: April 04, 2004, 04:25:00 PM »