Here is the detail:
I put about 30 g NaH in mineral oil in a 1000ml rbf. 500 ml of DMF added at rt.
Then ethyl acrylate 50 ml added at once. The temperature remained the same. No bubbling at all.
Then I went to the balance to weight something.
After about 15 min, the mixture became very hot. At the same time, a lot of gas was released. The reaction is so violent that it didn't stop until almost half of the orange colored mixture was pushed out of the rbf. What a big fountain!
Luckily nothing got hurt.
What happened?
the gas released during the accident was H2(trapped in a balloon which went upward showing the gas has lower density than air).
The smell of acrylate disappeared.
My conclusion is anionic polymerization.
The real question is
Did NaH deprotonate the a-proton of acrylate and initiated the reacion?
Tuesday, October 28, 2008
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4 comments:
My question is, how in the world did the mixture get colored orange??
Good question. I dont' really know the answer. maybe the polymer is organge ??
I'm very glad no one was hurt! I worked in an industrial lab for a few years and here are the immediate questions I asked to myself:
- Have you performed this reaction successfully on smaller scale before?
- Was all of the base dissolved in the DMF before you added the ethyl acrylate? This can be trivial on small scale, but when you go bigger, sometimes unforeseen problems occur. On a bigger scale, dissolving operations that are simple on small-scale can take a bit of time. Also, the heat generated from the dissolving process is much more appreciable on large scale. Suppose that the base wasn't completely in solution when you added the ethyl acrylate, then dissolution continued, and generated enough heat to spontaneously polymerize the ethyl acrylate. I think it's possible that this is what happened. To prevent this, you would stir the base/solvent mixture for a period of time, maybe 1 hour, to ensure homogeneity and dissolution, and also that the heat that was generated has disapated.
Alternatively, I would investigate the purity of the ethyl acrylate, if you have any left. Sometimes small impurities can have a dramatic effect.
Hopefully you can figure out what happened! Best of luck.
Thank you for your comment.
when scale goes up, everything changed.
I should pay more attention to those reaction.
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