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Suitable drying agent for grabbing residual polar droplets on surface of DCM

acacian

acacian

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Since DCM sits below the polar layer, this can mean very small water droplets can often sit on the surface when it is separated and drained. Unlike less dense solvents which sit above the polar layer, its not really possible to decant the polar droplets off without losing solvent - so for this reason I’ll often leave the tiniest bit of DCM in the funnel when draining to avoid this.

Of course I would prefer to get every last drop, so wondering whether adding a drying agent to absorb any water droplets might work well.

However..

I’ve read that using metallic compounds like Na2SO4 or MgSO4 can carry risk of delayed explosive reaction when mixed with halogenated solvents.. in this case I would not be shaking it to dry the DCM per se - just adding a bit to grab the water droplets from the surface and letting it sink to the bottom before decanting and filtering the DCM.

I was wondering whether someone might be able to offer some advice here. How much of a risk is this? Bearing in mind I would not really need to agitate the solution..

@Transform ?
 
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acacian said:
I’ve read that using metallic compounds like Na2SO4 or MgSO4 can carry risk of delayed explosive reaction when mixed with halogenated solvents..
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Are you sure about this? Do you have a reference? Halogenated solvents may explode with, e.g., metallic sodium, for sure. I'd be very surprised if there much of a reaction with something as inert as a sulfate salt.
 
I just came across a few people mentioning it on some chem forums so don’t have a reference I’m sorry. Ok, well that’s good to know anyways, thanks!
 
To obtain an explosive mix from halogenated solvents and alkaline metals you would need a heavily halogenated hydrocarbon and a very strong alkali metal in its pure elemental form. Carbon tetrachloride and sodium metal for exemple will explode when mixed together and even then it often requires a strong shock to initiate the explosion. DCM being a lighter halogen than CCl4 will require even stronger alkali like cesium to explode. Magnesium even at pure elemental form doesn't even have chance with DCM its impossible...let alone MgSO4. Neither NaSO4, you're worrying too much.

For separating DCM from aqueous droplets i just use a syringe to seperate the layers. If there's any small DCM droplets left in the basic solution i just add a small portion of DCM to it and suck it with a syringe.. you're putting too much though into this unnecessarily.
 
Thanks @neurobloom! Glad its not an issue.. yes probably overthinking here but just wanted to be sure it is safe. I find it quite finicky trying to remove small water droplets off of the surface of DCM.. so the idea of something like NaSO4 to absorb any residual water drops is appealing. Either that or I just get a syringe.
 
I also thought it’s usually preferred to use calcium chloride or molecular sieves because of the small risk that sodium sulfate has when mixed with DCM, I’m not sure if this is an issue for relatively short term use, or that prolonged contact is needed for this reaction to occur. Also I can imagine that it may matter what else is dissolved into the DCM.

In short if the vessel heats up it might be wise to have a bucket of cold water to cool it and a safe place to stand
 
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