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Topic: THF drying, color change  (Read 6530 times)

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Offline umair javed

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THF drying, color change
« on: November 08, 2012, 09:13:59 PM »
I am drying THF using sodium metal and benzophenone for my LAH reaction.
I refluxed the THF with sodium metal, distilled it and placed it in a bottle with molecular sieves. After 6 hours poured the THF from molecular sieves bottle into a fresh assembly of apparatus and repeated the above procedure with sodium metal for 36 hours and added benzophenone and its color is yellow (means still water there).
What could be the reason that it is still not dry?
I have been using dry THF (dried with sodium metal and benzophenone) without the molecular sieve drying as stated above but my reaction was not going with LAH.
Any suggestions that what problem I might be having with THF ( for my previous reactions the THF changed color to purple) ?

Offline willug

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Re: THF drying, color change
« Reply #1 on: November 09, 2012, 01:57:52 PM »
Could you explain what you did more clearly? It all sounds a bit confused, and maybe dangerous as a result.

Offline umair javed

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Re: THF drying, color change
« Reply #2 on: November 10, 2012, 04:35:31 AM »
Sorry for the unclear question.
I have to convert a ketone to alcohol. First I tried with NaBH4 but i didn't get the alcohol. again NaBH4 but not getting the product.

So I shifted to LAH. I used dry THF. tried 3 times with LAH, got my alcohol but in v.v.low yield, much of the quantity I recovered was my starting material (Ketone) from column.
Then I discussed with my professor, he said that may be your THF is not well dried. may be glasswares and bla bla... and he suggested me to repeat LAH reaction with careful drying of everything used in the reaction.

So this time when I was drying THF the colour was not changing to purple (which means THF is absolutely dry) when I added benzophenone. It changed to yellow color (which means still there is water). Even though refluxed it for more than 36hours.

ok leave the THF part but why my ketone is not converting to alcohol. Any suggestions or alternatives?

Offline mamid

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Re: THF drying, color change
« Reply #3 on: November 10, 2012, 07:46:51 AM »
Man, you might want to check your LAH. I had some surprises with this reagent, even from SEALED, albeit old, cans.

Offline umair javed

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Re: THF drying, color change
« Reply #4 on: November 10, 2012, 02:19:27 PM »
My labmate is using the same LAH for his reactions. Its working in his reactions.

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