The Stuck-hard Pyrex stopper

[Fortuna]

Yea, I know. Not exactly physical chemistry theory but a real world classic problem. Call me stupid , but....

 

I was making an aldehyde of an oil, an unobnoxius critter really, but it was/is dissolved in some methyl alcohol. I had in a flattened bot RB bottom ground neck flask. It needed to be dry for the next process and I had just remover it from the freezer. So I added some nice dry silica to it, and put the pyrex stopper in it, put on the mag stirrer on slow for a while, and let it settle. (oops !). I thought the warming up would offset the dessicant sucking up the water (and thinking for the dessicant would expand a bit as it hydrated).

 

Anyway, no luck, the darn pyrex stopper is really jammed on there thanks to my creating a vacuum inside.

 

I tried heating up up, and I observed the MeOH starting to boil. After it boiled for a little while, I tried to remove the stopper with no luck. As I watched it continue to boil, I thought to myself that this wasn't such a good idea, was it ? (if the stopper has acummulated some oil which has dried out it might be acting like glue, oh sheeet! ). Anyway, I aborted the boil and immediately gave it a cold water bath.

 

Any ideas on how to get that stopper out, short of breaking the neck of the flask ?

 

And please don't lecture me about Si grease. It would have contaminated the product in this case. Had to be done dry.

[reverse]

first you need to see what is holding that stopper in there.

 

examine the contact area closely with magnification.

 

if you come to the conclusion that it's just a simple air pressure differential holding the stopper in place, then use a syringe to inject air through the rubber stopper into the low pressure area.

 

If by Pyrex stopper you mean that the actual stopper is glass, then localised heat can be applied using butane pencil torch , they are handy and very inexpensive.

 

OK my small pea sized brain has taken a liking to this problem.

 

2: You use dry ice to freeze the stopper thus reducing the diameter of the stopper.

 

3: You hang the vessel from a string on frame., you then place the entire contraption inside another larger vessel and put a lid on that and create a vacuum inside the larger container to match the one inside the stuck vessel.

 

Yup, I like that last one.

[YT2095]

agreed, local heating would be my choice also, with gentle tapping of the stopper with something like a teaspoon.

 

brute force should be a last resort, but if you must, wrap both in nitrile rubber (for a good grip and splash protection), and use a twisting action as opposed to a pulling one.

 

Good Luck

[BenSon]

If there is a jar that i just can't open i always find putting it in freezer helps but this is a different can of worms. If localised heating dosen't work do as YT suggested using some stillsons for extra leverage would help out also.

 

~Scott

[Fortuna]

Thanks for all the advice. Well, I have to report that it ended badly with one casualty. The casualty was of course the $12 RB flask. To answer one poster's question, yes, it was a pyrex stopper, and that was one of my initial errors.

 

I really liked Reverse's idea of getting it inside some other vessel and pumping it down to a greater vacuum than what was in the flask. Unfortunately, the only suitable vessel I had was a vacuum dessicator, and this 250 ml RB flask would not fit inside it.

 

Anyway, I tried the local heating idea. I used a garden variety hardware store propane torch, and tried to evenly apply heat around the neck of the flask. I then tried to remove it with no luck. It was still stuck on hard.

 

But, as the neck cooled, the neck of the flask split (I heard it go "plink" ). I wondered now that occurred, but I think I understand it now. The ground neck and stopper are slightly tapered to make a good seal as the stopper is inserted. As I heated up the neck, the neck did expand, but as it did, the stopper got pulled deeper into the neck. As it cooled, the neck shrank around the stopper, and thus the plink.

 

The good news is that I recovered the solvent and aldehyde, nice and dry too. A small sample of the solution stayed nice and blue to a CoCl2.16H2O/MeOH reagent I made up for this purpose.

 

I try to learn from every experience and today I'll share that so others don't repeat my screwups. Anyway ;

 

- Use a rubber or cork stopper. In that way a needle could have been used to pump in some air and unvacuum it or might have been removable by hand.

 

- Start out colder if possible and work fast. Don't let it sit or if so burp it at regular intervals so as not to end up with such a high vacuum inside the flask.

 

- Better to use nonpolar solvents where possible (i.e. DCM might have worked here) and thus eliminating the need for drying, or at least making possible a pour through the dessicant drying process. Unfortunately, the common and cheap non-water polar solvents are usually so friggin hygroscopic they suck moisture from the air in no time.