What is the best way to measure and transfer a sticky compound in the lab, in particular for air/moisture sensitive reactions? I have a really sticky solid Wittig salt which I'm going to use in a Wittig reaction.
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$\begingroup$ PTFE (Teflon etc., e.g. sigmaaldrich.com/catalog/product/aldrich/z115282) may help if the salt is hygroscopic, since both polar (i.e. salt solution) and non-polar substances do not stick well. Silicone tools might also be of use. $\endgroup$– DrMoishe PippikCommented Dec 8, 2016 at 1:42
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$\begingroup$ Could you wrap it in plastic wrap? $\endgroup$– Joseph HirschCommented Dec 8, 2016 at 3:21
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$\begingroup$ Glovebox - you can fill it with a neutral dry gas. I would also suggest you checking the purity of your substrate - sticky solids usually mean impurities or solvent presence. $\endgroup$– vapidCommented Dec 8, 2016 at 13:47
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1 Answer
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Ideally, you want your sticky solid to already be in a Schlenk flask or similar. If it is unfortunately still in a normal bottle, take the weight of a Schlenk flask, fill in enough of the sticky solid and re-weigh. Note the difference, this is what you have in your flask.
Assuming that the sticky solid has a low enough vapour pressure (spoilers: practically all solids do), evacuate the Schlenk flask under high vacuum and backfill with argon (or nitrogen, if that is your inert gas of choice. Add a known quantity of your (dry, stored over molecular sieve and under inert atmosphere below a septum) solvent. Ideally, you either want an amount of solvent that gives you an easy-to-handle concentration (e.g. $10~\mathrm{M}$) or an amount so that what you need is in an even volume of liquid (e.g. $1~\mathrm{ml}$).
Finally, transfer the solution into your reaction flask.
If you need the sticky solid in different solvents and it is air-stable, you can evaporate the dry solvent at the rotavap. If not, keep it in solution under argon (or nitrogen). If the latter is the case, do your colleagues a favour and choose a standard concentration, not a good filling amount for exactly your reaction.
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$\begingroup$ I do wonder why this answer has been deemed ‘not useful’ or ‘unclear’. $\endgroup$– JanCommented Dec 11, 2016 at 0:44