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Home Audio Receivers Accessories home audio receivers.Home Audio Receivers Accessories home audio receivers InformationOrganic Chemistry ILAB EXAM: FINAL BROMINATION OF BENZENE SYNTHESIS AND PURIFICATION OF BROMOBENZENE: PROCEDURE DATA TABLE Chemical Boiling point C Melting Point C Density g/mL Solubility Benzene 80.1 5.5 0.88 Slightly in H2O Toluene 110.6 -93 0.87 Slightly in H2O Bromobenzene 155-156 -30.8 1.50 Insoluble Dibromobenzene 220.40 87.31 0.96 Insoluble MATERIALS: Graduated cylinder Weight scale Buchner funnel Filter flask Rubber stopper Hot plate Thermometer Conical funnel Various size beakers Fractionating column (for reflux) Various sized round bottom flasks Distillation head Condenser Vacuum adapter Clamps and stands Test tubes PROCEDURE: Pre Lab: The experiment should be carried out AWAY from the sunlight. Before beginning the experiment, we need to make sure that the benzene used in the experiment is free of toluene and water. To do this, we must put anhydrous calcium chloride into a flask of benzene to "dry" it and remove the toluene. This is then decanted into a vacuum filter, which will leave only pure benzene. Synthesis of Bromobenzene: Set up a reflux and place in a cold-water bath. In addition to setting up the reflux apparatus, set up an inverted funnel gas trap. This will collect the hydrogen bromide gas in the water and not in our lungs when the reflux takes place. Pour 2.3 mL of benzene in the round bottom flask of the reflux apparatus. After this, pour the iron (III) bromide (FeBr3) into the same round bottom flask. If there is a vigorous initial reaction, wait until this has almost stopped and then heat the water bath to a temperature of 25-30O C to initiate the reflux. Reflux at this temperature for an hour. After an hour has passed, raise the temperature of the water to 65-70O C, and allow refluxing for about 45 minutes. At this point, the color of the liquid should be dark. At this point, the reaction between the benzene and the bromide molecules should be complete. Purification of Bromobenzene: Transfer this liquid to a separatory funnel, and shake and vent with a 10% aqueous solution of sodium hydroxide. The lower layer should be the bromobenzene layer. Drain this layer out into a beaker. Add water to the liquids in the separatory funnel, and again shake and vent to ensure the absence of bromide. Drain if necessary. After the extraction, the bromobenzene solution needs to be dried. Again, put anhydrous calcium chloride into a beaker with the bromobenzene and shake. Set aside for about 30 minutes. Decant this solution, and filter this through a vacuum filter. Place the filtered liquid in a round bottom flask. Set up a distillation apparatus. Place the bromobenzene is a round bottom flask and distill into a clean flask. Collect the distillate only from between 150-160OC. Re-distil this liquid to obtain a more pure solution of bromobenzene. The liquid collected from this distillation should be between 155-156OC. It should be colorless and have a slightly "agreeable odor." This will be considered the "pure" bromobenzene and the reaction yield should be 80%. Purity tests: Test 1: Determine the boiling point of the liquid by measuring a boiling point range during the distillation. It should be close to 155-156OC. Test 2: Weigh the liquid and measure the volume. The density should be calculated. The density of bromobenzene is 1.50 g/mL. The calculated density should be close to this number. Test 3: Run the solution through a gas chromatography machine. Possible peaks seen in the gas chromatography could be from bromobenzene, benzene, toluene, and dibromobenzene. This means that there could be 4 major peaks, arranged according to boiling point. For the order, refer to the data table above. The peak for the bromobenzene should be the largest in percent area if this experiment has been successful. |