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Method for Grignard Reagent

Essay by   •  April 27, 2011  •  Essay  •  396 Words (2 Pages)  •  2,292 Views

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METHOD

1. Placed DRY 250 mL three-neck round-bottomed flask, fitted with a DRY water-cooled condenser and a DRY 125-mL separatory funnel on a water bath at 45-50oC. Placed a drying tube containing anhydrous calcium chloride to the top of the condenser and the separatory funnel.

2. Obtained 0.9g of magnesium turnings, a small iodine crystal and 10mL of anhydrous ether.

3. Removed the condenser (placed a small wad of in the cotton in the bottom of the condenser to prevent water going up the condenser from the steam bath) and added the magnesium and ether to the flask, then added the iodine crystal. With a DRY stirring rod, gently broke one or two magnesium pieces to expose a fresh surface. Replaced the condenser on the flask (removed the cotton wad).

4. Prepared a solution of bromobenzene in ether by dissolving 3.5mL of bromobenzene in 10 mL of anhydrous ether, and poured it into the separatory (dropping) funnel. Added 2-3 mL of this solution to the reaction flask and swirl the flask to mix the reagents thoroughly. Periodically lifted the flask from the water bath and noted the ether is refluxed without heat from the water bath. Once the reaction has commenced, added the remaining bromobenzene solution drop wise. When all the bromobenzene has been added, heated the reaction mixture for 20 minutes.

5. Placed a solution made from 4.3g of benzophenone and 10 mL anhydrous ether in the separatory funnel and begin drop wise addition of the solution to the phenyl magnesium bromide solution. Refluxed the mixture for 15 minutes using the water bath, after the addition is complete.

6. Cooled the solution to room temperature (it may solidify) and added 6M HCl (drop wise at first) until the aqueous layer and tested it with litmus. Added more ether as it was necessary because some had evaporated. Separated the layers, using a separatory funnel. Washed the aqueous layer with 15 mL of ether and combined the two ether fractions. Dried the ether solution with 1-2g of anhydrous sodium sulphate for 10 minutes and gravity filter the suspension to remove the drying agent. Evaporated the ether in a hood on a steam bath.

7. Purified the material that remains looks like brown oil by adding 25mL of 40-60OC petroleum ether. Swirled the product with this solvent for several minutes and then suction-filtered the mixture through a Buchner funnel. Sucked dry the solid, weighted it and calculated the percentage yield.

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