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Everybody digest, Vol 1 #307 -
"1. How to treat wet THF to bring the ppm levels of water down to say, 100 ppm.
2. What is the best way for making super-dry THF.
Q-1:
This is a much discussed question as to how to dry wet THF.
The age old method, that is still being used extensively in the third world countries is to shake THF with KOH flakes. (THIS IS A HAZARDOUS METHOD, AND BANNED THROUGH OUT WESTERN WORLD).
Alternatively, you can dry wet THF over Molecular Sieves, 4A type, properly activated.
(An excellent method for activating molecular sieves is to place them in a microwave oven (kitchen type, full power, 5 minutes)}.
TYPICALLY, IN INDIAN LABORATORIES, WE PASS THF THROUGH AN ACTIVATED ALLUMINA COLUMN. This not only gives the necessary preliminary drying of THF, but also eliminates the peroxides present if any. The alumina thus treated with THF must be considered as A PEROXIDE ITSELF, AND MUST BE DISPOSED OFF ACCORDINGLY. (the organic peroxides BIND to the Alumina strongly).
At an Industrial level, if you have a continuous necessity for distilling THF, you might employ an Alumina column. For one time use, it is NOT viable because, lot of THF will be held in the column (which is obviously a waste). Then, when to replace Alumina in the column? (when you get a Positive peroxide test for you THF and/or when the Moisture content exceeds that of the average five batches of THF you obtained from the same column. [ typically, for 5 Ltrs of THF we used about ONE kilo of Alumina. We never tried to re-use it, but I am sure, you can treat about 30 Ltrs of THF with ONE kilo of Alumina). This Alumina is then collected in Plastic cans and wetted with water and this is treated as Explosive/Hazardous/Flamable waste.
Q-2.
Lithium Aluminium Hydride is no longer a recommended drying agent for THF, inspite of its uncanny ability to remove peroxides. Best way is to treat the preveously dried THF with Sodium, reflux, cool, add Benzoquinone, reflux, await for the dark blue color to persist atleast for six hours, and then collect the liquid that boils at a constant temperature. In this case, you will not be accumulating huge Quantities of Sodium in your reactor vessel. Be abundantly sure that you do NOT have any leaks in your cooling system. Alternatively, if you have a FLAME and SPARK proof surrounding, go for chilled etheral solvents (dibutylether for example) for circulation in the condesor.
THE REASON WHY YOU MUST TREAT THE THF IS TO ENSURE THAT YOU DO NOT ACCUMULATE UNWANTED SODIUM IN HUGE QUANTITIES IN YOUR REACTION VESSEL.
I am sure you are experienced in treating multi kilogram quantities of sodium accumulated in reaction vessel. In some places it is recovered and converted into sodium sand or NaHMDS."