Organic Chem. Mini-lab 21 and 16

Organic Chem. Mini-lab 21 and 16 - E xp Number Mini 21/16...

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Exp Number Mini 21/16 Experiment/Subject Organic Chemistry I Lab Date 7/30/2010 Name: Valerie Dorsey Locker number 1 Chem. 2123-005 Free radical bromination of hydrocarbons Preparation/Purpose In this experiment we will compare the relative rates of bromination of a series of hydrocarbons: toluene, ethylbenzene, isopropylbenzene, tertbutylbenzene, cyclohexane, and methylcyclohexane. The reaction occurs by a free-radical mechanism in which the first (initiation) step involves the homolytic cleavage of bromine molecules to give bromine atoms. Equipment and Supplies: Approx. 250 ml beaker test tubes Physical Data : Choices for the hydrocarbons include: cyclohexane, methylcyclohexane, toluene (methyl benzene), ethylbenzene, isopropylbenzene (cumene), and t - butylbenzene.
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Procedure The reactions will be performed in three stages: 1. Addition of the substrate to the bromine at room temperature; 2. Any reactions which are not done after 20 minutes at room temperature will be put in a water bath at 50 o C; 3. Any reactions that are not done after 30 minutes in the water bath will be irradiated by a light bulb. _____________________________________________________________________________ 4. Bromine is a highly toxic chemical. 5. Do not breathe its vapors or allow it to come into contact with your skin because it may cause serious chemical burns. 6. Wear gloves when you are handling the bromine solutions, and keep them in the hood. 7. If you do get bromine on your skin, wash the area immediately with soap and water. 8. You may soak the area in 0.6M sodium thiosulfate solution for up to 3 hours if the burn is serious. 9. Bromine reacts with acetone to form a lachrymator - α -bromoacetone. 10. Do not rinse the test tubes with acetone before use, and do not use acetone to clean out any tubes still containing bromine. Set up a warm water bath – start with ~400 ml of hot tap water in a 600 ml beaker and put it on a hotplate set to 1. You want the bath temperature to be ~50 o C. Lights will be set up in the hoods. The hydrocarbon solutions (0.5 ml of substrate in 2.5 ml of carbon tetrachloride) will be in bottles in the hood. Place 3 ml of each solution in one of six small, labeled test tubes in a 50 ml beaker. Stopper them and move them to the hood in which you will be working.
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The bromine solution (1M in carbon tetrachloride) will be in a buret in the hood. Dispense 0.5 ml of the bromine solution into each of 7 large labeled test tubes. Use a 250 ml beaker to hold these tubes. Add 3 ml of CCl 4 to one of these test tubes, and label it “control”. Stopper all the test tubes and move to the hood in which you will be working. When you mix the solutions you will add each substrate solution to a test tube of the bromine solution, and agitate it to make sure it mixes. You will need to record the time at which the solutions are mixed and the elapsed time at which the bromine color disappears. The fastest reactions will be done in less than 20
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Organic Chem. Mini-lab 21 and 16 - E xp Number Mini 21/16...

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