Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: taurean on November 28, 2006, 06:25:04 PM
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Can someone help me with the workup of SmI2 (samarium(II) iodide) reaction? When I do workup with water and extract with ethyl acetate, I never see a clear separation of aqueous and organic layers in the Erlenmeyer flask.
Seeking advice from people who frequently use this reagent.
Thanks,
taurean
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You could try adding some NaCl, which may cause the aqueous layer to separate from the ethyl acetate.
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Maybe <a href="http://sanjayat.wordpress.com/2006/10/03/the-nmr-cap-trick/">this</a> will help?
Can't say I've ever used SmI2, though.
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You could try adding some NaCl, which may cause the aqueous layer to separate from the ethyl acetate.
I tried adding NaCl, it doesn't help.
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Maybe <a href="http://sanjayat.wordpress.com/2006/10/03/the-nmr-cap-trick/">this</a> will help?
Can't say I've ever used SmI2, though.
Nice trick. thanks.
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What was the solvent for the reaction?
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What was the solvent for the reaction?
Used 0.1 M solution of SmI2 in THF. So, I used THF as a solvent.
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I think whenever you are doing a work-up and don't get a good separation of the layers, it is because the densities of the two phases are very similar. What you need to do is change the density of either the aqueous or organic phase in order to see a separation. I think it is probably a coincidence that your SmI2 reaction didn't show a good separation - rather than this being typical of most/all SmI2 reaction workups.
Yggdrasil's suggestion of adding NaCl is one way of changing the density of the aqueous layer. Since this didn't work for you - try an organic solvent (for example CHCl3) which has a different density than EtOAc.
THF is a powerful cosolvent of aqueous and organic layers - you may also try rotovapping off some/most of the THF prior to adding your organic solvent for work-up. This may help, too.
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Yggdrasil's suggestion of adding NaCl is one way of changing the density of the aqueous layer. Since this didn't work for you - try an organic solvent (for example CHCl3) which has a different density than EtOAc.
I was under the impression that adding salt increased the ionic strength of the aqueous phase which decreases the solubility of organics in the aqueous phase, allowing the EtOAc to separate from the water. Similarly, adding another organic solvent like chloroform decreases the polarity of the organic phase which decreases the solubility of water in the organic phase, causing the two layers to separate. The density explanation makes sense though since having two layers with fairly different densities would allow an emulsion to separate easier.
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I agree that phase separations can be understood by considering the polarity of the organic phase and the ionic strength of the aqueous phase. One of the beauties of organic chemistry -- there are many ways to look at, understand, and approach a problem. :-)
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DaveD and Yggdrasil,
Thanks, for some nice input. I am going to try your suggestions.
My compound is highly polar. Decreasing the polarity of the organic phase might create some problems with the solubility of my product. Anyways, I will give a try.
I was reading in someone's thesis, that addition 1N HCl and sod.thiosulfate, during the workup would help. Let me know your comments.
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Sodium thiosulfate can be used to destroy excess iodine in the workup. It's not a bad idea to try that out. Is it possible that your molecule is getting protonated or deprotonated and then finding its way into the aqueous layer? Other good solvents for very polar molecules are dichloromethane and chloroform, so those might be worth a shot too.
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Can you change ethyl acetate by diethyl ether? and then the organic phase wash with a saturated solution of K2CO3 and a saturated solution of NaCl
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Can you change ethyl acetate by diethyl ether? and then the organic phase wash with a saturated solution of K2CO3 and a saturated solution of NaCl
I can try that. thanks.
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Can someone help me with the workup of SmI2 (samarium(II) iodide) reaction? When I do workup with water and extract with ethyl acetate, I never see a clear separation of aqueous and organic layers in the Erlenmeyer flask.
Seeking advice from people who frequently use this reagent.
I havent tried this reaction, but if you dont want to change extraction-solvent (you might check up your product-solubility in Handbook), try to add a little toluene to the ethylacetate. It works very well while working on diethylether/water extraction and the phases mixes into an emulsion. If toluene is miscible with ethylacetate (I believe it is), it might work here as well. Correctly in the diethylether/toluene system, you actually get a new emulsion in the organic phase, which drastically changes the density of the organic layer.
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I havent tried this reaction, but if you dont want to change extraction-solvent (you might check up your product-solubility in Handbook), try to add a little toluene to the ethylacetate. It works very well while working on diethylether/water extraction and the phases mixes into an emulsion. If toluene is miscible with ethylacetate (I believe it is), it might work here as well. Correctly in the diethylether/toluene system, you actually get a new emulsion in the organic phase, which drastically changes the density of the organic layer.
Thanks for the tip! As much as I hate toluene, I hate emulsions more, so I'll end up using it sometime. :)
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Oh, I've had this problem before. I was doing a water/DCM extraction in the workup of a methyl addition with MeMgBr. I did the reaction in THF too, the THF seems to be miscible in water and DCM, so you get a water layer, emulsion layer and a DCM layer.
Adding a bit of ethanol helps a bit, taking off the THF under vacuum before the seperation helps (but I quenched with water so this took ages).
The best way round it for me was to simply use a bigger seperating funnel and loads of DCM compared to water. You could try DCM in place of EtOAc maybe.
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I like to use Et2O in the workup for reactions that use THF because it is so easy to get rid of. Also, molecules soluble in THF are often soluble in diethyl ether too. DCM is my next choice if you need a more polar solvent, but the density switch isn't always easy to deal with. Moreover, emulsions of DCM and water are the worst!!
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I like the denisity. I find it much less hassle to collect the bottom layer from a seperating funnel, it tends to get less water in it. My supervisor has banned diethyl ether, due to it's flammability, and he hates the smell. We use tert-butyl methyl ether, which smells like sweets.
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My supervisor has banned diethyl ether, due to it's flammability, and he hates the smell. We use tert-butyl methyl ether, which smells like sweets.
Diethyl ether is my solvent of choice whenever I can get away with it. It smells wonderful, it doesn't melt my gloves (thankya DCM, chloroform, toluene...) and any morning that starts with an ether extraction just makes the rest of the day better.
What about the groundwater contamination with MTBE (underground storage tanks)? It isn't more expensive to dispose of the waste?
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I agree, isn't TBME worse than Et2O? It's less flammable, but much higher boiling (harder to get rid of) and pretty toxic too, I think. But I suppose if you chose dichloromethane, then you aren't so worried about the toxicity anyway. TBME must be a lot more expensive though, isn't it?
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Yeah I think TBME is more toxic, but the decision to use that over diethyl ether was not mine, I don't pay the bills, but I don't think the price difference is massive (I had a quick poke around on sigma-aldrich). Our solvent storage tanks are above ground, I have no idea of the disposal costs, it goes into the non-chlorinated waste tank with all the rest of them, and the department takes it from there. A significant proportion of the chemistry we do in our group is aqueous, so this cuts down overall toxic solvent use - although I'm not trying to use this as an excuse, I'm following workup procedures developed by the group and from papers that is my reason for using the solvents I use.
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I'm not telling you you're wrong! Please don't misinterpret what I said. I would make a different decision, but of course your boss is the only one that has that privelege.
I'm sure they just take all the non-chlorinated solvents and burn them. The safety difference is that ether, with a higher vapor pressure, has a higher possibility of explosion, but TBME is going to be worse if it gets spilled and gets into the ground water somehow. It's a judgement call. In our lab, ether is definitely much more common than TBME!
I have always wondered if aqueous chemistry is really that much safer because the disposal is so unregulated. It seems that traces of organic or organometallic species in aqueous phases is potentially more dangerous to the community than the controlled disposal of organics. Do you know anything about that? I might be totally off base.
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Sorry for digressing from your discussion.
The combination of diethylether and ethyl acetate worked best for my reaction.