Delloyd's Lab-Tech Chemistry
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- Drying agents
Solvent Purification and Drying
Anhydrous Ether :(C2H502O) FW = 74.12 bp = 34.6°C Put about 200 gms of anhydrous CaCl2 into a winchester (2.5 l) of ordinary grade diethyl ether, and leave standing overnight. Then filter through Watman NO. 1 filter paper into another winchester. Cut about 3 or 4 pieces of sodium sticks (1/2 inch long cuts) kept under paraffin oil, swab wipe dry with tissue, and put into the 1 mm die of sodium press using forceps. Extrude the sodium as "sodium wire" directly into the winchester which contains the filtered ether. Effervescence takes place as hydrogen is evolved from the sodium. When no more bubbles og gas are evolved, tne ether can then be used for the experiment.
Tetrahydrofuran (THF)FW = 72.11 bp = 65 - 67°C Pour 500 ml ordinary grade THF into a 1 liter flask, then add 10 g benzophenone. Use the sodium press and the 1 mm die to extrude about 5 g of sodium into it, stopper loosely, and leave to stand in a dark place (cupboard) overnight. When the contents go deep blue, indicating that peroxides and water has been removed, it is distilled under nitrogen in a prebaked flask containing about 2 g of freshly extruded "sodium wire". This should stay "bright" in the distilled THF.
Note : If the solution does not go deep blue overnight, add another 5 g benzophenone, and extrude another piece of sodium (2 g) into it, and reset overnight, then redistill.
Pet Ether(can use petrol) Extract with conc. sulphuric acid (100 ml H2SO4 and 1 liter pet ether). Discard acid extract and distill into flask under nitrogen and freshly extruded "sodium wire".
Dicyclopentadiene (cyclopentadiede dimer)FW = 132.21, BP =170°c Use a 100 ml RB flask and a short refractionating column, about 20 cm, lagged in asbestos or aluminium foil. Collect distillate at 40 - 42°C.
Disposal of used drying agent
1. Disposal of sodium/sodium wire :Ethanol is added slowly to react with the drying agent. There may be a delay in hydrogen evolution whilst surface contamination of the drying agent is dissolved. It is important to swirl the flask during the addition to ensure adequate mixing. When the evolution of hydrogen has ceased, a small amount (ca .15 cm3 ) of a 1:1 ethanol/water mixture is cautiously added. If no further hydrogen evolution occurs, water is cautiously added to fill the flask and it is left until no more bubbles of gas can be seen.
If an aqueous and an organic layer have formed, these must be separated, the solvent put into the appropriate waste solvent bottle and the aqueous layer washed down the sink with lots of water. If the water and solvent are miscible, often the whole contents of the flask can be washed down the sink with lots of water to render the mixture non-flammable.
2. Disposal of magnesium or calcium hydride :The procedure is similar to that used for sodium except that a mixture of 90% ethanol and 10% water is used in place of pure ethanol. When hydrogen evolution ceases, water may be added cautiously until no bubbles can be seen.
Similarly, as for sodium, if an aqueous and an organic layer have formed, these must be separated, the solvent put into the appropriate waste solvent bottle and the aqueous layer washed down the sink with lots of water. If the water and solvent are miscible, often the whole contents of the flask can be washed down the sink with lots of water to render the mixture non-flammable.