[mreff555]

Twice now I have lost my product attempting to use ethyl acetate to wash my product.
I can never get the product to recrystallize. This more recent time I had about .75g of actetasalicylic acid which I disolved in about 10 ml of ethyl acetate (yes I know I should have used less solvent.) Regardless, the instructions at that point told me to filter the product. but the mixture looks more or less homogeneous. Would typical filter paper actually trap the dissolved solids or would they bypass the filter. Regardless, I tried to remove some of the excess solvent by a very gentle controlled boil, held at 80°C. This is 50°C below the mp of acetasalicylic acid so I didn't see a lot of risk in loosing my product this way, however as best I can to I did.
So to some this all up, two questions.

1. Organic solids dissolve very well in ethyl acetate. will a sepratory funnel filter these solids at all, and of so will there be a high product loss? (assuming we are still talking about acetasalicylic acid.)
2. where was my thinking flawed in the slow heating of the solvent? How did I loose my product?

[sjb]

Seems to me that you're a bit confused over the proper use of a separatory funnel.



Where in this picture {disclaimer, this is not me, just a picture taken from wikipedia, consider PPE at all times} do you see a filter?

Consider the analogous situation where you have a crude mixture of salt (NaCl) and sand. In this case if you add enough water then it all dissolves. But you can recover some, if not all of the solid by evaporating off the water. If you add less water then predominately the NaCl will dissolve, and you can filter off the sand via Büchner funnel filtration or similar.



In your instance all the organic material has dissolved in your EtOAc, and broken some of the intermolecular bonds so that the resultant conglomerates are smaller than the holes in the filter paper. It's possible that you didn't heat it for long enough, or perhaps too gently (EtOAc only boils at around 78 °C, if I recall correctly) - perhaps try removal of the solvent on a rotovap or similar to recover your solid.

S

[mreff555]

Thanks for the reply, that answers a lot of questions.
First, I'm a moron. I realized that as soon as I saw the picture of a sepratory funnel. The instructions do call for one, but the instructor had set out buchner funnels. now I see why.

So I guess the problem, if I'm understanding you correctly was way too much solvent. which is what I originally figured. I'm thinking a better way to go about this in the future would be to just wash the solids dropwise while they are still being vacuum filtered. Either that or remove them from the vacuum filter, add them to a dry flask and add ethyl acetate dropwise, swirling, and stopping when I'm happy with the color of the crystals. Does this make any sense?

[James Newby]

if you are trying to recrystallise you need to heat the ethyl acetate up to just below its boiling point (i usually use a heat gun) and then add the minimum amount to your product flask in order to dissolve your product.  ie you want the hot ethyl acetate to be 99% saturated with your product.

If there is solid waste in the flask after your product has dissolved, the left over the solution needs to be filtered using heated apparatus to prevent recrystallisation.  I recently forgot to heat mine while recrytallising NCS and the crystals blocked everything.

To get nice big pure crystals pack an insulator (cotton wool) around the flask and allow to cool as slowly as possible, overnight is best.  The crystals grow nice and slowly, and no waste is trapped in the developing crystal structure.

After the crystals have formed, you can now do another filtration at room temperature, and make sure you wash the crytals with ice cold ethyl acetate to prevent them dissolving again.

Its a long process but a very effective way of getting a very pure compound.  Before modern technology this was the most commonly used technique for purification