Glass Stopcock Lubricant ?

Elementary · Fri May 06, 2005 3:18 pm

I have recently aquired a separating funnel with a glass stopcock. I have heard that strong alkalis will attack glass and possibly cause the stopcock to jam.

Are there any suitable lubricants I can apply to the stopcock before use that will prevent it from jamming and will also not dissolve in toluene ?

Star-light · Blacklight bulb

Silicon grease works. Buy it from a lab supplier.

2spun · The Resistor

Elementary,

yes very much so use a lube swiy was in a hurry use'd his nice new 1000ml
sep fun- (did not use lube) set it down for a few hrs. went to clean it. busted his nice new stopcock.
now swiy has to get some mapp gas and go hot. if that don't work well he has to come out of pocket$$.

bio · Working Bee

I gave up on glass stopcocks long ago but give PTFE tape a try. The thin white stuff stretched tight and maybe no overlap. Teflon tape works great instead silicon grease on ground joints even under vacuum if properly applied and also you can get teflon paste and standard taper sleeves.

Worth a try and won't get into everything, being very difficult to get off if a little too much is used.

primathon · modified

Greasing a glass stopcock is not that difficult. Remove the stopcock, and lightly cover the entire surface in a very thin layer of pure silicon grease (or if you have access to lab-specific lubricants, Apiezon M or N) with your fingertip. This process can be improved upon by heating the stopcock with a heat gun beforehand, so the lube gets into all the little nooks and crannies. Insert the stopcock back into it's mount, and twist repeatedly until you are satisfied the lube is getting everywhere it needs to. There should be no bubbles or streaks. If you do get streaks, adding more grease is not the answer. Remove the stopcock, clean both it and the mount with hexane (or another suitable solvent), wipe clean, and try again.

Elementary · Sat May 14, 2005 9:24 pm

Is silicone grease not soluble in toluene ?

Can't seem to find chemical resistance data for silicone grease on the web

I really don't need grease contamination in my non polar.

Star-light · Blacklight bulb

IndoleAmine · Dreamreader Deluxe

High vacuum chemical-resistant silicone grease designed for laboratory application on glass joints indeed IS soluble in nonpolars (the worst is DCM Wink

), but this is not much of an issue with toluene: the correct way to operate separatory funnels is to drain the lower layer, and then close the stopcock and pour out the remaining upper layer through the top opening. This way, you ensure that no droplets of the other layer contaminate what you're trying to isolate.

And this is the reason why DCM (and other heavy nonpolars) is a bit problematic sometimes, but toluene normally shouldn't be much of an issue here.

Besides, you can tighten the screw of your stopcock nicely when you have greased it properly before - and then the surface between interior liquid and lubricant is at most 0.001% of the grease's total surface - minimal contamination... Wink

Of course it is advisable not to use heaps of silicone grease when gassing amine freebase/toluene for example Smile

, but for vacuum distillation and similar applications, the use of said grease is a must and the benefit of being able to move the joints freely seen as more important than avoiding trace contamination of your solvent.

Besides, you will redistill your solvent regularly when recycling...

2spun · The Resistor

swiy agrees w/ all said avec the grease lab grade etc..
The heavy NP's was a new thing for swiy. aka-(DCM) very problematic as swiy has just learn'd it don't act as most the NP's swiy has used.
PTFE, stopcocks are great. make sure one has enuff O-rings for the size of that PTFE stopcock as well them there things ware out fast.