Organic Chemistry Lab 315 Fall, 2014

1. Organic Chemistry Lab 315 Fall, 2014

2. DUE DATES • Today • At beginning of lab – Gas Chromatography Report • At end of lab -- copy of laboratory notebook pages for today's experiment • Spectroscopy Problem II #3 • Next Week • Distillation of a Mixture Report (see my web page for special instructions) • Spectroscopy Problem II #4

3. In Lab Today • Your vial of caffeine will be returned. Please discard the contents in the Waste Jar, rinse the vial, and return the vial to the Instructor’s bench. • Distillation (separation) of a mixture of ethyl acetate and butyl acetate by Simple Distillation and Fractional Distillation.

4. In Lab Today • Simple and Fractional Distillation. • The mole percent composition of the ethyl acetate/butyl acetate mixture is unknown. • You will compare the efficiency of Simple vs. Fractional Distillation in separating these two components. • “Efficiency” is determined by how well the mixture is separated into its components • The closeness of your calculated mole % composition for the two procedures to the actual composition will be the measure of efficiency.

5. Distillation of a Mixture • Simple Distillation of a pure compound. • Most of the compound distills around the boiling point. Graphs of Volume of distillate vs. Temperature • Simple Distillation of a mixture where boiling points are very different or a Fractional Distillation. • The two compounds are efficiently separated. Each component distills around its boiling point.

6. Distillation of a Mixture Temperature vs. time behavior of a single component during distillation Temperature vs.time behavior of two components with similar boiling points Temperature vs.time behavior of two components with very different boiling points

7. Distillation of a Mixture • Simple Distillation • Relatively pure substances can be separated from a mixture if the boiling points of the components differ by >100oC or if impurity <10%. • EtOAc (b.pt. = 77oC) BuOAc (b.pt. = 125oC) • Fractional Distillation • Separates components by distilling them through a longer path with more vaporization-condensation cycles (just like re-distilling over and over again).

8. Experimental Procedure • Set up distillation apparatus • Simple or fractional (which you do will be decided later) • Put mixture of EtOAc/BuOAc in distilling flask with boiling stones • Be sure to position thermometer correctly • Conduct distillation slowly but steadily

9. Experimental Procedure • Collect fractions in test tubes. • The liquid that distills over a 5-deg. interval is collected in one test tube. • It may be a large or small volume of liquid. It doesn’t matter. • If you accidently mess up an interval, write down the actual temperature interval and then proceed with a new 5-deg. interval.

10. Experimental Procedure • Measure the volume of each fraction. • Save fractions until you are finished. • Place three fractions in vials, properly labeled. • Beginning, middle, end • The saved fractions will be analyzed by Gas Chromatography next week.

11. Experimental Procedure • You are going to graph Volume of Fraction vs. Temperature • For a single pure component, all the volume would be collected near the boiling point, as in your purification of the unknown for IR spectroscopy. • Expect to collect the most volume at the temperature(s) nearest the boiling point of each component. • See the graphs on a previous slide.

12. Notes • Measure volume of unknown mixture with graduated cylinder, ±1.0 ml. • Wrap fractionating column and head with Al foil. • Collect all fractions in test tubes, over ICE!. • I need to check your set-up before you begin the distillation – have everything ready except turning on the hot plate. • Control distillation rate (~ 1 drop/sec) by moving the distillation apparatus up or down (only if necessary). Too fast a drip rate will decrease the amount of separation. • WASTE Distillation waste in marked jar in hood.

13. Notes • In the fractional distillation, you may have to increase the heat to reach the boiling point of BuOAc. • Each fraction is collected over a 5-degree temperature interval. • Save all fractions until the experiment is over. • Place 3 fractions from each distillation in individual vials, properly labeled. (Beginning, middle, end from each distillation) • Remember: boiling points may not exactly match the literature. They should be close. • You will analyze the fractions next week using Gas Chromatography.

14. Notes • Working in Groups – • One Pair = 2 students who conduct a distillation together, either simple or fractional. One Group = Two pairs (1 pair = simple; 1 pair = fractional) will pool data to analyze. • No member of the Group may leave the lab until the distillations are completed and all the data are recorded in everyone’s notebooks (record all group members’ names near the top of your notebook copy) • Something always goes wrong, or differently, among the pairs. Be sure that everyone in the group understands everything that happened unexpectedly – whatever – and PUT IT IN YOUR NOTEBOOK BEFORE LEAVING THE LAB. It will be Your fault if you do not understand the data, whether or not you did that particular distillation. • See my lab web page for special instructions on writing the Report. • Make a photocopy of your report before turning it in next week. You will need to refer to it for following week’s experiment: Gas Chromatography of Distillate Fractions

15. Lab Clean-up • Khoa Tang