The Vespiary
The Hive => Methods Discourse => Topic started by: guyincognito on August 10, 2002, 02:00:00 PM
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Swim was thinking that it took too long to add all the preformic to the iso/dcm in the modified performic so swim decided to ice bath the iso/dcm to speed things up (he got the idea from classic performic (acetone)which was ice bathed).
Well it went fine for awhile and swim thought this would save lots of addition time, but all of the sudden dcm gas came out like it was a fire hose from the top of the flask. Swim didn't feel real good and it took awhile for the gass to stop coming off.
Not really sure why it happened. All swim knows is it shouldn't be tried at home.
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Exothermia->happens when one doesnt follow directions.
GODISNOWHERE
Shoot Narcs, Not Drugs
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The two phase peracid oxidation is one of my favourites. I never start heating untill all peracid has been added. The exothermic reaction makes sure their is enough heat for the first two hours or so. Just add aliquots of lets say 5 mL and monitor the temperature. I did it a couple of times and my empirical experience now is of great value, especially yield wise ;) .
Be careful with DCM. Boiling point is low (40C) and if inhaled as a gas, rather noxious.
Doped(TM) since 19.... euhm... a long time :)
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Baal always takes a paper towel, gets it a little bit damp, rolls it up and sticks it in the top of the condenser. This helps in holding back the DCM without 'plugging-up' the setup. Never have applied heat to a buffered performic/DCM reaction, shouldnt have to. That is unless you live in Alaska. Stirring is most important with these reactions, mag stirring requires more reaction time than with a good overhead setup. Drip addition is the key to a smooth reaction that will carry itself with little need for babysitting.
GODISNOWHERE
Shoot Narcs, Not Drugs
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thnaks baal, thats a good idea, swim has inhaled enough dcm.
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Baal has also found that these run great in the summer months where ambient temp is around 60f or less at night. Heres a quick tip(if you own a freezer) for easy long lasting ice water for condensers; Take a five gallon bucket and fill it half way with H2O, cap it, then freeze it. Pull it out and add another gallon of icewater to it, toss your pump in and away you go. Baal makes up 2 or 3 ahead of time and it works out great for longer runs and such.
GODISNOWHERE
Shoot Narcs, Not Drugs
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The DCM isn't going to keep the 2-phase reaction at 40C if you add the acid extremely fast. It will help some, but since the DCM is not in solution with the reacting peracid and isosafrole, it can only transfer heat away from the outside of the polar liquid mass. The cooling efficiency will improve with the efficiency of the stirring because there is more surface area contact between the polar and nonpolar liquids. Since you say you were using an Ice bath, I imagine you weren't getting a good vortex going in the flask with your stirbar. What probably happened is the organic layer got incredibly hot and then finally hit a point where the DCM became increasingly soluble in it and was quickly boiled out the top. Since DCM takes very little energy to evaporate and the organics - water, formic acid, etc. - hold their heat relatively well, it would have been very difficult to contain the DCM even with a large condensor.
Don't take shortcuts unless you have a good idea about what you are doing. If you had pulled that fast addition bullshit with the classic performic using acetone, you could possibly be very badly burned and cut right now. Take this as a learning experience and try to get the basics down before you start dialing in your reactions.
All paths are the same: they lead nowhere