Please help, i dont understand how to do the mmoles for isolated yield or how to find theoretical yield in mg or mmoles or percent yield! Attached is the entire lab i if necessary!
1. Place 24 mg of magnesium ribbon cut into small pieces in a dry test tube. Add 200 mL of anhydrous ether using an automatic delivery pipette.
2. In a dry vial prepare a solution of 100 mL of bromobenzene in 500 mL of anhydrous ether. Transfer a small amount of this solution to the test tube containing the magnesium turnings using a Pasteur pipette. Swirl the mixture while warming by hand. Watch for the formation of bubbles on the surface of the magnesium. If there is no sign of reaction, gently use a glass stirring rod to crush the pieces of magnesium. This will expose a fresh metal surface. Once the reaction appears to be refluxing well, add the rest of the bromobenzene solution in portions. After all the bromobenzene solution has been added, continue to warm the reaction mixture by hand until most of the magnesium has disappeared. Cool the mixture to room temperature.
3. Prepare a solution of 140 mg of benzophenone in 400 mL of anhydrous ether in a vial. Using a Pasteur pipette, carefully add the benzophenone solution drop wise to the Grignard solution at a rate that maintains a gentle reflux of the ether. Rinse the vial that contained the benzophenone solution with 100 mL of ether, and add it to the reaction mixture. Swirl the mixture for 1-2 minutes, and cool it to room temperature. Magnesium salts are the by-products of the reaction and usually solidify at this stage.
4. Hydrolyze the magnesium alkoxide salt by careful, drop wise addition of 1 M HCl from a Pasteur pipette. At the same time, use a glass stirring rod to break up the solid. Excess magnesium will react vigorously with the HCl, so be careful. If the mixture boils rapidly, cool the test tube in an ice bath. If the ether layer boils off, add more ether to maintain liquid in the test tube. Continue adding HCl and mixing with a stirring rod until the aqueous phase tests acidic (red) with litmus paper. Either too little or too much HCl can lead to a decreased yield of triphenylmethanol.
5. Transfer the lower aqueous layer to an extraction tube. Save the ether solution separately, as it should contain most of your product. Extract the acidic aqueous layer with three 0.5 mL portions of ether. Each time remove the upper ether layer with a Pasteur pipette. combine these extracts with the original ether layer. Extract the combined ether layers with 0.5 mL of cold water to remove any acidic residue. Dry the ether solution over 300 mg of anhydrous MgSO4. Decant the organic layer from the drying agent into a tarred vessel. Rinse the drying agent with some fresh ether and combine the rinsings with the original organic layer. Remove the ether by evaporation in a stream of air until the sample looks dry. Make sure the tubing to the air outlet is dry first.
6. Add 0.5 mL of cold hexane to the crude triphenylmethanol in a test tube. Using a glass stirring rod, crush the solid and swirl the mixture to release impurities into the hexane. (Note: This process is called trituration). Collect the purified triphenylmethanol by vacuum filtration using a Hirsch funnel. Rinse the crystals with 0.1 mL of cold hexane. Air dry the triphenylmethanol.
