EQUIPMENT
    Hot plate with magnetic stirrer, microscale glassware kit and heating block, gas chromatograph.

SUPPLIES
    Safety goggles,  isopentyl alcohol, glacial acetic acid, concentrated sulfuric acid, 5% aqueous sodium bicarbonate, magnesium sulfate, Pasteur pipets, distilled water, acetone.

PURPOSE
    To synthesize isopentyl acetate.

PROCEDURE

1. Assemble the reflux apparatus according to written and verbal directions.  The teacher will review this process before the van visit. See Figure 1.
2. Take a 3.0mL conical vial with a magnetic spin vane, and add 1.0mL of isopentyl alcohol (a) using a micropipettor preset to 1.0mL by the teacher.
3. Add 0.550mL of glacial acetic acid (b) using a preset micropipettor
4. Add four drops of concentrated sulfuric acid using a dropper.
5. Heat the mixture to a boil in a heating block on the hot plate (be sure to stir the mixture with a magnetic stirrer.)
6. After the reflux band (the band where the vapors recondense and flow back into the vial) is visible, continue heating under reflux for 20 minutes.  Maintain the temperature between 160 ^oC and 180 ^oC
7. Remove the apparatus from the hot plate and allow the mixture to cool to room temperature.  Air cool for a couple of minutes and then use a beaker of water to speed cooling. Do not turn off the hot plate.

CAUTION:  Do not place the vial in the water until it has cooled sufficiently to avoid cracking the vial.

8. YOU MAY STOP AT THIS TIME IF NECESSARY.  TRANSFER YOUR SAMPLE INTO THE NUMBERED PLASTIC VIAL PROVIDED AND STORE UNTIL YOUR NEXT LAB PERIOD.
9. While waiting for the vial to cool, prepare a 5mL conical vial with 2mL of 5% aqueous sodium bicarbonate solution (NaHCO₃).  NOTE: The micropipet can only deliver 1mL, so use it twice.  You will be transferring your refluxed solution to this vial for extraction later.
10. Use a Pasteur pipet to transfer your solution to the 5mL conical vial prepared in step 9.  Wait for the initial fizzing to subside, then cap the vial.
11. For this extraction, shake the capped vial and vent additional gas (shake and vent three times), then allow to stand until separate layers are formed.
12. Using a Pasteur pipet, remove the lower, aqueous layer and discard it into a waste collection beaker or sink.
13. Extract again by adding a fresh 2.0mL portion of 5% NaHCO₃ solution to the 5.0mL conical vial.
14. Again, shake and vent three times, then allow to stand until separate layers are formed.
15. Using your Pasteur pipet, again remove the lower aqueous layer and discard it.
16. Dry the organic layer by adding a small amount of anhydrous MgSO₄ (this amount varies depending on how much ester you have made - please see instructor.)
17. Clean the 3mL conical vial by rinsing with distilled water and finally rinsing with acetone.

STOP!!  IF YOU HAVE LESS THAN 40 MINUTES LEFT, DO THE FOLLOWING:

a)  Preweigh your clean, dry sample vial with its cap and record its mass.
b)  Transfer your sample to the vial using your Pasteur pipet, leaving the drying agent behind.
c)  Weigh the sample vial and contents and determine the mass of the ester by subtracting.
d)  Clean the 5mL conical vial by rinsing with distilled water and finally rinsing with acetone.
This concludes the synthesis portion of the lab.  If you have 40 minutes or more, your teacher may have you purify your ester sample by distillation, or you may proceed directly to the gas chromatographic analysis.

PURIFICATION BY DISTILLATION:

18. Using your dropper, transfer the dry organic layer (containing the ester) into the clean, dry 3mL conical vial, leaving the drying agent behind.
19. Assemble the distillation apparatus according to written and verbal directions.  See Figure 2.
20. Add the dry screw-type magnetic spin vane to the ester.
21. Begin distillation and continue it until only one or two drops of liquid remain in the 3mL conical vial.
22. During distillation, pre-weigh a sample vial and record its mass.
23. When distillation is complete, transfer your pure banana oil (isopentyl acetate) from the Hickman still to the pre-weighed sample vial using a new Pasteur pipet.
24. Weigh the sample vial and contents and determine the mass of the ester by subtracting.

25. Following your teacher's instructions (See page 15-18 of the Teacher Reference Section), inject one µL of your sample into a gas chromatograph.  Identify and label the peaks and their retention times on your print-out.  Compare your results with those of the known standards.  Complete the data table using your printout.

Calculate the percentage yield of the ester using the following steps and data from your experiment.

1. Calculate the number of moles of isopentyl alcohol used (from Procedure step 2.)
                                                                                                    (MW = 88.2 g/mole, density = 0.813 g/mL).
 
 
 

4. Calculate the theoretical yield.
 
 
 
 
 

 Mass of your product and vial         _________g

 Mass of your vial only                     _________g

 Mass of your product                      _________g
 
 

Gas Chromatograph Code            A           B                       Circle the appropriate code.

Be sure to use retention times for standards from the GC on which your sample is run.
 
 

QUESTIONS

1. Why did you not find any acid in your final sample?
 
 
 

2. Why did you find water in your final sample?
 
 
 
 

3. How could you have reduced the amount of water in your final sample?
 
 
 
 

4. Why did you find isopentyl alcohol in your final sample?
 
 
 
 

5. How could you have reduced the amount of alcohol in your final sample?
 
 
 
 

6. By following the best possible techniques, which peaks should be minimized, which should be maximized?
 
 
 
 

7. How did your group compare to others in your class/school?
 
 
 
 

8. What suggestions would you have to improve your results?