Organic Chemistry Lab 315 Fall, 2013

1. Organic Chemistry Lab 315 Fall, 2013

2. DUE DATES • Today • At beginning of lab – Synthesis of tert-Pentyl chloride • At end of lab -- copy of laboratory notebook pages for today's experiment • Next Week • Synthesis of Cyclohexene Report • See my lab web site for instructions

3. Report Notes – Last Week • Two important items were required (and were included as part of the Instructions): • Attach the distillation graphs from the Distillation Report • Make a comparison of the mole percent composition as calculated from the fractional distillation from two weeks ago and the GC peak areas from last week.

4. In Lab Today • Synthesis of cyclohexene • The mechanism of the reaction is E1 Step 1 is an acid/base reaction between H3PO4 (acid) and alcohol (base) to form the oxonium ion. Step 2 is the dissociation of the oxonium ion to form the cyclohexyl carbocation and the good leaving group, H2O. Step 3 is the acid/base reaction between the H-atom on the carbocation and the base, H2O, resulting in overall elimination.

5. In Lab Today • Synthesis of cyclohexene • The mechanism of the reaction is E1 Step 1 is an acid/base reaction between H3PO4 (acid) and alcohol (base) to form the oxonium ion. Step 2 is the dissociation of the oxonium ion to form the cyclohexyl carbocation and the good leaving group, H2O. Step 3 is the acid/base reaction between the H-atom on the carbocation and the base, H2O, resulting in overall elimination.

6. In Lab Today • Synthesis of cyclohexene • The mechanism of the reaction is E1 Step 1 is an acid/base reaction between H3PO4 (acid) and alcohol (base) to form the oxonium ion. Step 2 is the dissociation of the oxonium ion to form the cyclohexyl carbocation and the good leaving group, H2O. Step 3 is the acid/base reaction between the H-atom on the carbocation and the base, H2O, resulting in overall elimination.

7. In Lab Today • Reaction takes place within a distilling round-bottom flask. • Cyclohexanol and H3PO4 are mixed, and they begin to react as the flask is heated. • As the products,cyclohexene and water form, the cyclohexene distills out of the reaction mixture.

8. In Lab Today • Cyclohexene has a lower b.pt. than cyclohexanol. • The cyclohexanol and acid remaining in the distilling flask continue to react as the equilibrium shifts because the product cyclohexene is removed. • The elimination reaction will continue until all the cyclohexanol has reacted.

9. In Lab Today • The receiving flask now contains cyclohexene with a small amount of aqueous acid. • Add solid NaCl, which “salts out” the organic cyclohexene from the aqueous phase. • Add aqueous sodium bicarbonate until the aqueous layer (which one?) tests basic to litmus.

10. In Lab Today • Two phases are the upper cyclohexene phase (with some water and aq. base) and the lower aqueous phase with dissolved base and NaCl. • Separate the phases (keeping upper phase in funnel). • Wash the cyclohexene layer with water (removes ___?) • Review drying organic solvents (See p. 696 in Pavia)

11. In Lab Today • Dry cyclohexene with anhyd. Na2SO4. • Decant cyclohexene into clean dry pre-weighed vial. • No distillation; no qualitative analysis tests. • Take refractive index and IR. • Store in drawer, labeled.

12. Experiment Notes • Use a funnel to deliver liquids through neck of round-bottom flasks, separatory funnel, vial. • You must heat the cyclohexanol/acid mixture slowly. Never let it go above 100 deg. B.pt. cyclohexene (?_) • This is not a distillation, but rather a reaction that needs to get going first. • Please clean up used pipets after doing refractive index and IR.

13. Waste • Dispose of aqueous solutions in the sink with plenty of water.

14. Synthesis Report • See the instructions on the web site for writing a Synthesis report. • Pay particular attention to the table on the Report Form, which is actually a calculation of theoretical yield. • The phosphoric acid is a catalyst and so it is not included in the balance equation nor used for determination of theoretical yield. • Separation scheme (flow chart of procedure for separating a pure product from reaction by-products)