10-31-03 16:29
No 468043
I have been reading a bunch of different methods people dry THF, some descriptive, some not. One of which using CaH2 is as follows:
Tetrahydrofuran, b.p. 65.4°
As THF is completely miscible with water it is best not to take any chances as to it being wet. THF should be first refluxed 24 hours over calcium hydride (10 g per liter) then distilled for use in the ketyl pot. Sodium preparation is similar to that for diethyl ether, the final wash of course would be with THF. THF's ketyl is a deep purple color.
So im not to sure what this "ketyl pot" is but im guessing it has something to do with the further drying of benzophenone and sodium wire. I then read that some people dry their THF using KOH, and then this benzophenone/sodium mix, however it is unclear to myself how they dry the THF in KOH. Is it refluxed also, then distilled out, or dried over, as with anhydrous magnesium sulfate when drying methanol?
This removal of H2o in THF seems to be a world wide headachs as I read many comments about people having trouble obtaining anhydrous THF, mainly due to the inconsistencies in purity from suppliers. I have some KOH, some benzophenone, yet no sodium wire, can NaCl be used in replace of sodium wire??
Maybe the KOH would be enough if repeated numerous times? My THF isn't dangerously wet, as a rxn was performed using THF that was dried over MgS04 (2x) and as I have learned, that didn't do anything in removal of moisture.. so I may have well not even bothered and used the THF straight. Yields were horrific so it has to be dried heavily this time to eliminate that factor. Ahh well.. back to the drying board.
http://www.greenspun.com/bboard/q-and-a-
(Chief Bee)
11-01-03 08:17
No 468131
it is unclear to myself how they dry the THF in KOH
I believe stirring them together overnight, following by decanting is the procedure, as KOH hold less water at higher temp.
can NaCl be used in replace of sodium wire??
No way...
And you are correct about the "ketyl pot". It is further described in ../rhodium /equipme
(Hive Bee)
11-01-03 08:40
No 468136
Thanks Rhodi, I missed that link..
Benzophenone Ketyl Study
The procedure in the article describes adding 5 grams of sodium, and 30 grams of benzophenone to 3 liters of tetrahydrofuran.1 The mixture is then refluxed under inert gas until the blue color of the benzophenone ketyl forms. The author of the article states that "once the blue color forms, distillation of the solvent will yield very pure, dry, oxygen and hydroperoxide free ether."1 However, the author provides no data on the purity or water level of the solvent produced from this method. We decided to carry out a study on the benzophenone/sodium still to obtain these answers.
So this is done under a gas such as Argon? If swim set up a 2L single neck flask with a reflux condensor attached to that, and a balloon filled with argon to the top of that.. this would be ok during a reflux reaction?? Is no pressure released when THF is refluxed?
http://www.greenspun.com/bboard/q-and-a-
(Newbee)
11-01-03 09:25
No 468143
If you are able to make the Argon flow slowly into the reflux condenser the argon will push out all the air.
Hippler
(Chief Bee)
12-29-03 19:16
No 479731
(Rated as: excellent)
Sodium Benzophenone Ketyl Solution
(Taken from Inorganic Syntheses #21)
Ph2CO + Na -> Na[Ph2CO]
Caution: Sodium metal is highly reactive. It should be handled under a covering layer of mineral oil and an atmosphere of dry nitrogen.
Procedure
A 50 mL, two-necked, round-bottomed flask is removed from a hot oven and flushed with nitrogen. A sample of benzophenone (0.091 g, 0.5 mmol) together with 20 mL of freshly distilled and deoxygenated tetrahydrofuran (THF) and a stirring bar are placed in the flask. A small lump of sodium metal (~0.5 g) is cut into smaller pieces directly into the flask against the emergent stream of nitrogen. The second neck of the flask is then closed with a septum cap. The mixture is stirred for 0.5-2 h in the stoppered flask under nitrogen until the initial ultramarine blue is replaced by an intense blue-purple color. The resulting solution is ~0.025 mol·L-1 in Na[Ph2CO]. This solution may decolorize in 1 or 2 days' time but it can be regenerated by addition of more benzophenone.
Properties
A solution of sodium benzophenone ketyl is exceedingly reactive, and is immediately decolorized by air or traces of water, alcohols, and so on. The solution should therefore be kept under nitrogen at all times. Aliquots may be removed using a dry syringe via the septum cap. Under these conditions, the solution appears to be stable for ~2 days.
The Hive - Clandestine Chemists Without Borders
(Hive Bee)
01-04-04 09:46
No 480373
Don't do that! It is very dangerous, since LAH reacts violently with any water present in THF and it might ignite spontaneously.