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Topic: LiAlH4  (Read 19572 times)

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Offline sw2672

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LiAlH4
« on: July 24, 2006, 03:08:23 AM »
The reduction of amide was carried out with LiAlH4, and then I tried to obtain the desired product from crude mixture.  However, it seems to be very hard to extract it from the gelated LiAlH4 after adding water.  Is there any better way to extract from LiAlH4?
I had tried to use wash with CH2Cl2 after adding small amout of NaOH(aq). But this way did not give satisfied yield. The prodcut seems to be captured in the crude.  Please help me
« Last Edit: July 24, 2006, 08:08:30 PM by sw2672 »

Offline movies

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Re: LiAlH4
« Reply #1 on: July 24, 2006, 08:35:29 PM »
You need the Fieser & Fieser workup!

It's really easy: if you used X milligrams of LAH, make sure your reaction is cooled to 0 degrees C, then add X microliters of water (Slowly!  There will be bubbling!), then X microliters of 15% aq. NaOH, then 3X microliters of water.  Warm to room temp., then stir the resulting mixture rapidly for about an hour and you should get a nice flaky white solid.  Dilute up with a little more ether (or THF) and filter through Celite or filter paper.  Wash with ether (or THF), dry your filtrate (with Na2SO4 or MgSO4) and you should be good to go!
« Last Edit: July 26, 2006, 12:55:18 AM by movies »

Offline sw2672

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Re: LiAlH4
« Reply #2 on: July 25, 2006, 08:51:50 PM »
When 1g of LAH was used, 0.001ml of water have to be added?  It seems to be too small amount of water.  Please check out the unit.

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Re: LiAlH4
« Reply #3 on: July 26, 2006, 12:54:30 AM »
When 1g of LAH was used, 0.001ml of water have to be added?  It seems to be too small amount of water.  Please check out the unit.

Oops!  Sorry, should be milligrams of LAH, not grams.  I fixed it above.

Offline nottingham

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Re: LiAlH4
« Reply #4 on: August 13, 2006, 04:12:21 PM »
Usually there are two kinds of method to reduce the amide to amine;
one of them you can use the Red-Al solution.
the other one you can prepare the AlCl3/LiAlH4 solution: firstly dissolve the freshly sublimed AlCl3 in Et2O, then add the solution of LiAlH4 in THF to the above solution at zero degree. after stirred for about half an hour, then you can add the above solution to your substrate. for the work-up you only need to add water slowly then extraction.

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