Organic Chemistry Lab 315 Fall, 2016

DUE DATES Today Next Week At beginning of lab – Gas Chromatography Report At end of lab -- copy of laboratory notebook pages for today's experiment Spectroscopy Problem II #4 Next Week Distillation of a Mixture Report (see my web page for special instructions) Spectroscopy Problem II #5

Simple and Fractional Distillation In Lab Today Simple and Fractional Distillation Distillation (separation) of a mixture of ethyl acetate and butyl acetate by simple distillation and fractional distillation. You will compare the efficiency of Simple vs. Fractional Distillation in separating these two components.

In Lab Today The mole percent composition of the ethyl acetate/butyl acetate mixture is unknown. “Efficiency” is determined by how well the mixture is separated into its components (similar to “resolution” in chromatography). The closeness of your calculated mole % composition for the two procedures to the actual composition will be the measure of efficiency.

Distillation of a Mixture Simple Distillation of a pure compound. Most of the compound distills around the boiling point of the compound. 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.

Distillation of a Mixture Temperature vs. time behavior of a single pure compound 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

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).

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

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.

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.

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.

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 heat. 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.

Notes In the fractional distillation, you may have to increase the heat to reach the boiling point of BuOAc. Remember: boiling points may not exactly match the literature. They should be close. WASTE Distillation waste in marked jar in hood.

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 page). 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

Lab Clean-up Abani, Djanabou Hull, Sara