Figure 1 Figure 2 Chem 334 Expt. #3 Simple and Fractional Distillation; Analysis of Distillation Fractions by GC CHEM 334 Expt 3 Lecture

What factors affect the boiling point of a compound? 22 C (degrees) difference, need about 12 theoretical plates to separate these two liquids. CHEM 334 Expt 3 Lecture

Experiment #3 compounds EA = ethyl acetate CH3CO2CH2CH3 EP = ethyl propionate CH3CH2CO2CH2CH3 b.p. = 77oC b.p. = 99oC 22 C (degrees) difference, need about 12 theoretical plates to separate these two liquids. CHEM 334 Expt 3 Lecture

Where would you expect the boiling point of a mixture of ethyl acetate and ethyl propionate? 22 C (degrees) difference, need about 12 theoretical plates to separate these two liquids. CHEM 334 Expt 3 Lecture

See Techniques 2 and 3 Where would you expect the boiling point of a mixture of ethyl acetate and ethyl propionate?

Boiling Point - Composition for a Liquid-Liquid Mixture Raoult’s Law “mixture of two liquids will have a b.p. that is between the b.ps. of the pure liquids” PX = PoXNX where PX is the partial pressure of X PoX is vapor pressure of pure X NX is the mole fraction of X in mixture (Exception: Azeotropes)

x moles of EA and y moles of EP What would be the mole ratio? Assume a mixture of x moles of EA and y moles of EP What would be the mole ratio? What would be the mole fraction of EA in the mixture? 22 C (degrees) difference, need about 12 theoretical plates to separate these two liquids. CHEM 334 Expt 3 Lecture

Boiling Point - Composition for EA - EP mixture Total vapor pressure of mixture “Ptotal” is the sum of the partial pressures due to EA and EP. Ptotal = PEA + PEP If “Ptotal” is equal to the external pressure, boiling occurs.

CHEM 334 Expt 3 Lecture

Your experiment: We will do two distillations: A simple distillation and a fractional distillation. Work in teams of two: One student sets up the simple distillation and the other student sets up the fractional distillation glassware. 22 C (degrees) difference, need about 12 theoretical plates to separate these two liquids. CHEM 334 Expt 3 Lecture

Table for Simple (Fractional) Distillation Temp oC # drops Record your data: Temp. & # drops 1 4 8 12 70 etc. Also collect data for Fractional Distillation

Simple Distillation Set-up Thermometer position collect the 1st two drops here, in a receiving vial. Label! * Add boiling chip Figure 1

Continue recording your data

Fractional Distillation Set-up Micro-column & steel sponge Do not “stuff” the column too tightly Be careful not to cut your hand with the steel sponge when packing the column. * Figure 2

Simple & Fractional Distillation Plot Both Curves on one Graph Temperature Plot both S1 and F1 curves on the same graph 98 oC oC 0 4 8 12 16 20 24 28 …………………..etc. Volume of distillate (# drops)

Part C. Analysis of Distillation Fractions by GC HP 5890 Gas Chromatograph

Flow Diagram for a Capillary GC Sample Injector Carrier Gas GC Detector vent Open Tubular Capillary Column

Gas Chromatography A separation method for volatile compounds A chromatography method: Stationary phase and moving phase Separation is based on physical & chemical properties of each compound different interaction with the stationary phase A true microscale method!

Each peak (in a good separation) represents one compound. Retention time Injection point

Each peak (in a good separation) represents one compound. The area under each peak corresponds to moles of the compound

Gas chromatogram of a 50:50 (v:v) EA/EP mixture In diethyl ether EA EP Remember: Diethyl ether ≠ Petroleum ether !!!

Next time: Gas chromatography (conclusion) Steam distillation: Isolation of eugenol from cloves