My precious compound spilled out of a bottle and sticked onto a piece of plastic foam. the foam was dissolved by the dcm which is the solvent with my compound.
Discard it ? no, the boss will kill me.
1 I cut the foam off and dissolved the foam (with my compound) with DCM/EtoAc.
The foam dissolved without problem. concentrated. passed a pad of silica gel, eluting with etoac, nothing can be removed.
2. checked the structure of the foam through internet, it is polystyrene,
http://en.wikipedia.org/wiki/Polystyrene
tried to run a TLC with pure polystyrene, no obvious spots.
3. tested the solubility of the foam in organic solvents.
soluble: dcm, etoac, ether
unsoluable: meoh, hexanes,
4. so meoh was added to precipitate the polystyrene, and a simple filtration with silica gel removed the plastic.
Showing posts with label accidents. Show all posts
Showing posts with label accidents. Show all posts
Monday, August 17, 2009
Monday, November 17, 2008
Finally, another accident revealed the source.
Something happened during an overnight refluxing methanol rxn.
There are the clues I found:
1. somehow the red alcohol in the thermometer became un-continuous. there are gas between the red-alcohol.
2. the hot plate was cold although the knob is still on the right position. Restarted the hotplate returned the heat.
3. What is more, the mineral oil bath became darker than before.
4. although cooling water is running, half of the methanol was gone. (open container reaction)
My conclusion is the hot plate is bad. It heated up to a very high temperature sometime in the night! The high temperature exceeded the range of the thermometer and destroyed it. Also it darkened the mineral oil.
This hotplate is the same one I used for the other accident! SEE PIC!
the mechanism of controlling temp of this kind of hot plate is by a electromagnetic relay. I can hear the "click" sound when it started to heat. When the temp reached a preset value, the clicking sound became intense.
It is not reliable. Never use this kind of hotplate!
There are the clues I found:
1. somehow the red alcohol in the thermometer became un-continuous. there are gas between the red-alcohol.
2. the hot plate was cold although the knob is still on the right position. Restarted the hotplate returned the heat.
3. What is more, the mineral oil bath became darker than before.
4. although cooling water is running, half of the methanol was gone. (open container reaction)
My conclusion is the hot plate is bad. It heated up to a very high temperature sometime in the night! The high temperature exceeded the range of the thermometer and destroyed it. Also it darkened the mineral oil.
This hotplate is the same one I used for the other accident! SEE PIC!
the mechanism of controlling temp of this kind of hot plate is by a electromagnetic relay. I can hear the "click" sound when it started to heat. When the temp reached a preset value, the clicking sound became intense.
It is not reliable. Never use this kind of hotplate!
Sunday, November 9, 2008
Once again, another lab accident.
This time it is a sealed tube reaction.
solvent is methanolic HCl (about 3-6 M, 10 ml). ace galssware 50 ml seal tube (max. 60 psi) with teflon cap.
temp is only 80-90 C. magnetic stirring.
after about 5 hr, somehow, the teflon cap was unscrewed (by itself !) and popped up to the ceiling of the fume hood along with all the solvents and reactants.
the reaction was not supposed to generate any gas.
the solution was green, which was not observed in a previous run.
the magnetic stir bar was broken after the explosion. magnetic metal inside can be seen.
Luckily, nobody get injured because of a protection shield we have.
Also nothing got broken. the seal tube is still intact and looks ok.
what is going on?
I guess the defective magnetic stir bar was the reason, which generated H2 gas in the presence of HCl. this is also explained why the color is green.
What is interesting is I still can not image how the tight teflon cap managed to unscrew itself.
In an early similar accident I had half a year ago, the sealed tube was just destroyed by the inside pressure.
solvent is methanolic HCl (about 3-6 M, 10 ml). ace galssware 50 ml seal tube (max. 60 psi) with teflon cap.
temp is only 80-90 C. magnetic stirring.
after about 5 hr, somehow, the teflon cap was unscrewed (by itself !) and popped up to the ceiling of the fume hood along with all the solvents and reactants.
the reaction was not supposed to generate any gas.
the solution was green, which was not observed in a previous run.
the magnetic stir bar was broken after the explosion. magnetic metal inside can be seen.
Luckily, nobody get injured because of a protection shield we have.
Also nothing got broken. the seal tube is still intact and looks ok.
what is going on?
I guess the defective magnetic stir bar was the reason, which generated H2 gas in the presence of HCl. this is also explained why the color is green.
What is interesting is I still can not image how the tight teflon cap managed to unscrew itself.
In an early similar accident I had half a year ago, the sealed tube was just destroyed by the inside pressure.
Tuesday, October 28, 2008
Another lab accident .
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?
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?
Saturday, July 12, 2008
LAH explosions
Accidents happen without sign. really?
1. LAH explosion.
years ago when we still have LAH pellets in the lab, you have to powder it to use.
One day I was puhching it in an open container. Suddenly there was an explosion. Not a big one, but really scaring. Hopfully there was only 1 pellet of LAH. only the powder of LAH cautht on fire, the pellet was still intact.
2. another LAH story.
when I quench a LAH reduction(big scale), water was first used. You are supposed to add water slowly. But how slow? I don't konw. One day, addition of water was a little quicker , but still under control, I thought. Then suddenly, boom... liquid in the bottle jumped out. Hopfully, there was no stopper on the neck and I was not touched. What happened? the water added was coated by LAH, when the stirring is not quick enough to break the water drop, it will explode.
1. LAH explosion.
years ago when we still have LAH pellets in the lab, you have to powder it to use.
One day I was puhching it in an open container. Suddenly there was an explosion. Not a big one, but really scaring. Hopfully there was only 1 pellet of LAH. only the powder of LAH cautht on fire, the pellet was still intact.
2. another LAH story.
when I quench a LAH reduction(big scale), water was first used. You are supposed to add water slowly. But how slow? I don't konw. One day, addition of water was a little quicker , but still under control, I thought. Then suddenly, boom... liquid in the bottle jumped out. Hopfully, there was no stopper on the neck and I was not touched. What happened? the water added was coated by LAH, when the stirring is not quick enough to break the water drop, it will explode.
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