Sciencemadness Discussion Board - Drying Aldehydes properly - How to do it?

Drying Aldehydes properly - How to do it?

LuckyWinner - 5-10-2020 at 05:22

aldehydes, when made and filtrated from aqueous solution can be quite moist.

would placing this wet paste into a desiccator under vacuum with
anhydrous calcium chloride be sufficient to draw all the water out?

once it reaches dryness, grind up in a mortar and repeat the desiccator drying process.

dryness indicator would be by visual inspection if the sample appears dry and can be
grinded into fine powder?

this will work with any aldehyde that is a solid at room temperature?

[Edited on 5-10-2020 by LuckyWinner]

njl - 5-10-2020 at 05:32

Yes that would probably work. Why not dissolve in a dry solvent and add a drying agent? That would be a lot faster.

LuckyWinner - 5-10-2020 at 06:11

Quote: Originally posted by njl

Yes that would probably work. Why not dissolve in a dry solvent and add a drying agent? That would be a lot faster.

true,
another question.

whenever I extract, for example, an aldehyde with a solvent,
shake it in the separatory funnel.
I ll end up loosing a lot of solvent inside the aqueous layer...

any way to prevent the solvent from getting 'swallowed' unrecoverable by the water?
salting out with NaCl? but this may interfere with the product that is getting extracted...

I know every solvent has its own 'soluble in water' data, this cant be avoided or minimized?

with drying solvent you mean , to dry the solvent before it is used
in an extraction?

why is that of use if the solvent is getting in contact anyhow once you
extract the aldehyde from an aqueous solution?

Tsjerk - 5-10-2020 at 06:35

What solvent are we talking about? Adding NaCl to your aqueous solution seems like the most straightforward way to keep the solvent (ethyl acetate?) out. It also shouldn't interfere with extraction of anything organic out of the water, it would probably only help.

LuckyWinner - 6-10-2020 at 01:03

Quote: Originally posted by Tsjerk

What solvent are we talking about? Adding NaCl to your aqueous solution seems like the most straightforward way to keep the solvent (ethyl acetate?) out. It also shouldn't interfere with extraction of anything organic out of the water, it would probably only help.

diethyl ether,
by adding NaCl to the aqueous solution till its saturated will push out
all water bound diethyl ether?

for example Im always losing 30ml every 500ml of aqueous solution that
is shook heavy in a sep funnel.
some due to evaporation

you need to add the NaCl before you extract with ether or after,
or it doesnt matter?

diethyl ether
solubility in water (6.05 g/100 ml at 25 °C)

unionised - 6-10-2020 at 01:26

Quote: Originally posted by LuckyWinner

you need to add the NaCl before you extract with ether or after,
or it doesnt matter?

You add teh salt before extracting it.
Though it might be instructive to try doing it the other way.
Shake some water with ether.
Draw off the water layer.
Add salt to it and see how much ether comes out of solution.

LuckyWinner - 6-10-2020 at 02:49

Quote: Originally posted by unionised

Quote: Originally posted by LuckyWinner

you need to add the NaCl before you extract with ether or after,
or it doesnt matter?

as example
100ml water is extracted with 10ml diethyl ether

you recover 5ml of ether
the you add NaCl to the water till you see the other 5ml emerge from
the water?

this way you dont waste NaCl and just add more salt till your complete
ether is recovered?

Tsjerk - 6-10-2020 at 05:03

I'm pretty sure unionised meant it is just interesting to see how much ether you can get out, just out of curiosity.

NaCl costs <1 euro / kg, just dump in about 20 grams per 100 ml and stir until dissolved. Then extract with ether. Also I would use a bit more than 10 ml ether, more like 30, as this will minimize mechanical losses. If your ether is more precious you can try to recover the ether by distillation.

Edit: the amount of NaCl you can dissolve may vary depending on what else is in your water layer. I would keep adding salt NaCl until nothing more dissolves and then use 80% of that.

[Edited on 6-10-2020 by Tsjerk]