07-19-04 23:22
No 520329
I know that there are several posts on the subject but as far as I know this one is the highest yielding. This is barely due to the master princple of chemistry which I try to understand : Knowing what is going on in the flask.
We accomplishy this by: You add H2SO4 to dehydrate the alcohol, but due to its capability of oxidation yo may also oxidize the I- to I2. But, as you know whats goin' on there, you interfere this disadvantage of H2SO4 by adding al and re-reducing it. Thats simple, easy and high yielding.
This way tried by SWIM and this is the first time he succeeds after wastind 600grms of KI :(
So you can be sure that EVERY word is real and gives the major sound of victory.!!!!
First, prepare 100mls MeOH in an erlen. 100mls of H2SO4 was dripped over it. When finished it was put in a 100ml sep funnel (in portions) stiuated in the thermometer adapter of a distillaqtion apparatus. fill a RBF w/ 150 grms of KI dissolved in 200mls of hot H20, it was rigged to the y adaspter , cond. placed and water starter runnin thru. The RBF was brought boiling w/stirring and hhe HMeSO4 was dripped at a rate of 2 drops per second. Reciecver was plunged under ice+water and 5 mins later oily drops of MeI was seen as a bottom layer in the reciever and at some time (approx. 30mls of MeI was produced) the reactor produced a purple I2 color.. The HMeSO4 solution was stopped dripping therm. adapter (and sep fun) was disconnected for a second and 5g thick al foil was added. therm ad.+sep fun. placed again and distillation continued. While Al removed the purple, MeI continued to distill over. 100mls MeOH and 50g of KI dissolved in 100mls H2O was added at once. 50mls of acid was prepared in the sep funnel, and when no purple was visible , acid was dripped at the same rate above, whereupon more MeI produced. But towards the end purple vapors formed. Swim acted immediately by adding 5grms of thick al foil, which cleared the pu0rple. Distillation started and the rest of the acis was added till no oil formed.
The MeI was pulled w/a pipette, washed w/ thiosulfate dried over CaCl2 and put in a bottle w/ small silver pieces. (washing was done with an ice cold thiosulf. sol and crushed ice in a small sep fun.)
Gert ready to hear : The yield is 51mll.....!!
In old times swim was happy w 10ml with the same amount of precyrsors. Sometimes he couldnt get more than a few drops. What a SUCCESS:!
--The further additions of acid dehydrate the rxn producing more MeI but if there isnt enough MeOH, HI reduces the acid. So if you see white smoke add MeOH immediately, take it off from heat.
-Even if you add excess MeOH from the start dont forget that it distills over during the procedure (I collected 380mls of distillate.
-Al reduces I2 and removes the purple color. Acid oxidizes the AlI3 and produces HI, this HI can be oxidized by the acid to I2, it can oxidize the acid to H2S(Caution!!) or (the best) it adds to the methanol to give MeI and H2O. The last step is the rate limiting step. The more H2O you have the less that equation goes right.To reduce the amount of H2O, use mnimum H2o to dissolve KI and use dry reagents.
In the above writeup, swim managed this condition by disilling the rxn contents as much as he could. (MeOH is bound by the acid as HMeSO4, so there is not much of a loss as an azeotrope w/ H2O - if you dont add it at once, sluggishly). This also removes the formed HI And he also added extra acid at a rate that it wont interfere w/the HI.
Using too little water may cause side rxns (the interferation of HI with H2SO4)
due to the concentration
But as always, there is an easy way for the lucky and rich. P2O5, H3PO4+KI is an excellent, high yielding way to produce HI. But this method has yielded far more than the phosphoric acid + KI, for me.
This MeI can be used in a variety of ways like building PTC catalysts, forming grignard reagents and so on. The high volatility, huge molecular weight with an intense cost for non-experimental thoughts (Commercial ideas- which I have no business) unstability are the disadvantages.
I, presonally dont believe that its a carcinogen (according to my personal researchs, alkylating dna is a hard business for a weak methylating agent like MeI but very easy for DMS which REALLY methylates in a VERY EXHOTERMIC AND A VIOLENT WAY! And high MW means less toxicity per one average inhaation - but dont take my word for it) A breath of MeI DOES cause dihheria and nausea so never ever breath it (never forget ice cubes in the reciever and be sure to plunge it under icecubes+water.)
P.S. : Silver stabilizes the MeI. Always keep it in an amber bottle, best stored in the freezer (everyone eatin from there will slowly be poisoned but I assume meI is more important to a bee :)))
Sorry for long post
Just wanted to share the preperation of a really important ad expensive regent that every ether frolic needs.
Thanx for reading ;)
