[ivanakaj]

I need a good cook for the reduction od esters to alcohols with NaBH4, what I need is a good procedure how to extract the alcohol from the water-ethanol mixture.
i tryed CH2CL2, but i'm feeling that's not good enough, yields are low, i think my alcohol, witch is a very small is staying in ethanol and water mixture.

i know it's a silly question, but..

[StarvinMarvin]

Did you try ethyl acetate? Sometimes it works better. Or even try CHCl3 instead of dichloromethane.

[alphahydroxy]

Erm, not really sure what a "good cook" is...

OK, so if I've got this straight, you are doing a reduction of an ester by dissolving the substrate in ethanol/water, and adding a solution of NaBH₄ in ethanol/water to it?

Using such solvent mixtures will often cause problems in work-up when dealing with relatively polar products, so it's not all that surprising that your product is split between phases - i think this is where the issue arises from.

Could you perhaps simply evaporate the ethanol/water from the vessel, then apply the residue to column chromatography?

Or maybe use neat THF or ethanol or methanol in place of the ethanol/water system? This should be easier to evaporate...

Or use DMF (can't remember bout the solubility off the top of my head though) as the solvent. If done on a small scale (say 1 or 2 mL of DMF), you might be able to apply this straight onto a column without bothering to work it up...

These may or may not work! I can't be held responsible if it cocks up !

[StarvinMarvin]

DMF as the solvent for reduction? It will be the first one to go

[azmanam]

DMF as the solvent for reduction? It will be the first one to go

same with ethyl acetate, though, right?

nm, you were talking for extraction, not reaction solvent.

[Squirmy]

Are you sure your reaction is reaching completion? Reduction of esters with NaBH₄ generally requires special substrates (e.g. an OH/NH near the ester) or forcing conditions.

[StarvinMarvin]

I think LAH would be better for esters.

And as far as NaBH4 is concerned, you can try performing the reaction in methanol. At least, it's easier in workup.

[Arctic-Nation]

While I've got my doubts about using NaBH₄ to reduce esters, I've had some good experience with doing difficult extractions at 0°C or even lower temperatures. The solvents separate a lot easier when they're cold, and the change in solubility of any organic compound will probably work in your favour.

Alternatively, but this doesn't always work, you could try adding NaCl to the mixture to force your product into the organic layer.

And as has been suggested before, evaporating the water-ethanol mixture will also work. Add toluene, use a rotavap as a Dean-Stark trap and you're set.

[kiwi]

Agreed, no reason to shy away from lithal, it gets the job done quick and easy. As long as you're smart about it, workup is a cinch, and can be done without resort to aqueous extraction. If you want to avoid LAH, lithium borohydride will reduce esters, but don't count on sodium borohydride doing the job - as previously mentioned only certain esters are reactive enough.

I think LAH would be better for esters.

And as far as NaBH4 is concerned, you can try performing the reaction in methanol. At least, it's easier in workup.

[ivanakaj]

LAH doesn't work on this particular compound.....only NaBH4 works, I see the reduction is done by TLC. I do the reaction in ethanol because that's what they use in the paper i found, but they don't give any supporting material on the experiment condition. so i found that you extinguish the reaction with water( because of the left over NaBH4, because it's added in excess). and that is how you get the ethanol/water mixture. If I put it directly to rotavapor, the temerature would have to be high, and my compund has a low boiling point too.
so i want to extract it from this mixture.
i tried CH2Cl2, and ether....they don't work so well.
i'l try ethyl acetate...if i do the reaction in methanol, what will change? methanol has a lower boiling point, but it's not jet low enugh....

[James Newby]

Have you tried LAH? Very strange that LAH doesnt work yet NaBH4 does, do you have other functional groups that are LAH sensitive?

[ivanakaj]

don't think so, i have a N near by the ester.....i guess because the mechanisam of the LAH and NaBH4 are completely different one works, and the other does not...

[Squirmy]

Could you post a structure of your starting material?

[James Newby]

One of the reasons LAH was designed is to reduce esters so the actual reaction shouldnt be a problem.  Ive successfully reduced carboxylic acids to alcohols with LAH, its VERY good at reduction!

As your product is an alcohol i would suggest avoiding other alcohols as solvents.  Use CH2Cl2 or ether as they are easy to remove and should dissolve your product.

As squirmy said post your starting material and the product you are expecting and maybe we can help some more.

[Arctic-Nation]

One more thing I've thought of, but I'm not sure it would be a good idea to use in this case: evaporate the solvent when the reaction is complete, then add ethyl acetate (or any other solvent that doesn't mix with water) and water.