URGENT help needed: Synthesis of crown ethers for deadline of Master's Thesis

[Chris28]

Hello everyone,

I think this could be a pretty long post, just so you know.

I'm a Master's student Bio-Engineering, and for my thesis I have to synthesize '15-crown-5 ' crown ether. I have been trying to do this in the laboratory for the past 4 months, without any decent yields. I am following an older protocol of Smid et al. 'Substituent Effects on  the stability of cation complexes of 4'-substituted monobenzo crown ethers'. It is the image without the yellow text.

I added the protocol here.

It's been quite a disaster really. After numerous tries I've only managed to synthesize about 2 grams... As my background is more environmental sciences and not organic chemistry, I really could use some help also using this forum. The setup is a normal reflux setup in the beginning, and I use a rotavapor to evaporate the solvent. Then there is an extraction step (discussed below).

Is there something I'm missing in the protocol? Especially the extraction step (they talk about continuous extraction?) is a problem I think, I tried with a Soxhlet extraction but the oil seeped in the tubes. Also we just added the hot heptane to a beaker with the oil for extraction, is our extraction the biggest problem? (According to another paper by Sousa et al., image shared here as well).  

I would need 10 + grams of this compound, so how it's going now it's not happening.

I am praying for help from people with experience in this, or people that could add anything to the protocol...

Thanks so much.

Christophe 

[hypervalent_iodine]

It does sound like your extract is a bit dodgy. Can you tell me how much oil you’re typically getting from this compared to what you get out at the end? I’ll respond more in a bit about the continuous extraction.

[hypervalent_iodine]

Okay, so your problem is that you’re using the wrong by of equipment. A Soxhlet extractor is not used for continuous liquid liquid extraction, it’s used for extracting things out of solids. You need a different bit of glassware. It’s not all that common though, so you might find it hard to get a hold of. My suggestion would be to use normal partition in a separatory funnel with room temp solvent. You might have to do this several times. 

 

FTR, what you need if you wanted to keep going with continuous extraction looks like this:

 

 

[Chris28]

On 15-2-2018 at 11:12 PM, hypervalent_iodine said:

It does sound like your extract is a bit dodgy. Can you tell me how much oil you’re typically getting from this compared to what you get out at the end? I’ll respond more in a bit about the continuous extraction.

Hey man, thank you for the answer.

After the evaporation of the solvent it is a big volume reduction: from 200 - 300 ml total solution (solvent and reagents etc.) to about 20-30 ml maximum. Yes we thought that our extraction step could be wrong

On 16-2-2018 at 12:23 AM, hypervalent_iodine said:

Okay, so your problem is that you’re using the wrong by of equipment. A Soxhlet extractor is not used for continuous liquid liquid extraction, it’s used for extracting things out of solids. You need a different bit of glassware. It’s not all that common though, so you might find it hard to get a hold of. My suggestion would be to use normal partition in a separatory funnel with room temp solvent. You might have to do this several times. 

 

FTR, what you need if you wanted to keep going with continuous extraction looks like this:

 

 

Any idea where I can find this type of glasswork online?

Also, isn't the same problem going to be there? That the oil just seeps

through the below tube back in the boiling flask because it's the heavy phase.

Thanks

Edited February 20, 2018 by Chris28

[hypervalent_iodine]

I have no idea. My building is lucky enough to have its own glass blower, so we just get things like that made up for us. If you are at a University you could try and contact some organic chemistry labs and see what they have. 

 

Also, I’m not sure I’m seeing what you mean by oil seeping out? I suspect you are missing the point of what continuous extraction is. Depending on which layer you want out of the partition, you would choose either a higher arm or a lower one. In your case, you’d want the higher one I think. That way, when your heptane boils and drips down into your oil, only the heptane layer should then run out into the round bottom flask when it fills up. These are normally done with a more traditional partition, say with water and some other organic solvent, and looks like this: