Distillation Dehydration of an Alcohol: GC MS

1. Distillation & Dehydration of an Alcohol: GC MS

2. Things to do Dehydration reaction Distillation: 1. Fractional Distillation 2. Simple Distillation Characterization of product by GC MS

3. Distillation Process of vaporizing a liquid, condensing the vapor, and collecting the condensate in another container. Liquid ? Vapor : Vapor ? Liquid Liquid and Vapor always in equilibrium. Liquid Vapor

4. Distillation If your compound is pure and single component: Temperature remains constant during distillation process so long as both vapor and liquid are present.

5. Distillation If you have mixture or impure compound: Temperature increases throughout process because composition of vapor changes continuously. Composition of vapor in equilibrium with the heated solution is different from the composition of the solution.

6. Uses To Separate liquids with different boiling point especially in Petroleum Refineries.

7. Uses To purify liquid samples. 1.Alcoholic beverages distilleries 2. Chemical factories.

8. Types of Distillation Simple Distillation. Fractional Distillation Vacuum Distillation. Steam Distillation.

9. Simple Distillation Single vaporization- condensation cycle of a mixture that produces a distillate that is always impure at any temperature range between the range of boiling points of the components. Therefore, it is impossible to completely separate the components in a mixture with simple distillation.

10. Simple Distillation Relatively pure substances can be obtained from a mixture with simple distillation if the boiling points of the components differ by a large amount (>100? C) 1. DMSO � Diethyl ether (~ 155 ?C). 2. DMSO � DMF ( ~ 40 ?C).

11. Simple Distillation Setup

12. Simple Distillation Ideally a distillation will efficiently separate liquids in the order of increasing boiling points. Actually incomplete separations (with sample overlap) often occur, especially with liquids of similar boiling points and/or physical apparatus of lesser fractionating capability.

13. Fractional Distillation Accomplishes the same thing as multiple simple sequential vaporization-condensation cycles, by inserting a fractionating column between the distillation flask and the distilling head.

14. Fractional Distillation Long Stainless � steel mesh filled Short Stainless � steel mesh filled Glass bead filled Vigreux (Glass Condensation) All improve the separation process by increasing the surface area available to establish liquid : vapor equilibria.

15. Fractionating Column

16. Fractional Distillation Set up

17. Factors Affecting Distillation Type of mixture: The greater the difference in the boiling points of two compounds the easier it is to separate them by distillation.

18. Factors Affecting Distillation Physical setup: Not only does the setup enclose and direct the migration of vapors, it provides an internal surface to promote vapor / liquid equilibrium, helping establish a temperature gradient

19. Factors Affecting Distillation Temperature control: More defined vapor / liquid equilibrium and temperature gradients can be established if heat is not applied too quickly and insulation is used to minimize temp. fluctuations

20. Factors Affecting Distillation

21. Heating Sources

22. Ideal Solutions An Ideal solution is one which obeys Raoult�s Law. 1. Hexane � Heptane 2. Benzene � Toluene 3. 1- Propanol � 2 - Propanol

23. Raoult�s Law Raoult�s Law: In a solution of two miscible liquids (A & B) the partial pressure of component �A� (PA) in the solution equals the partial pressure of pure �A� (PAo) times its mole fraction (NA) It works only to Ideal solution

24. Raoult�s Law Partial Pressure of each component in an Ideal solution depends: 1. Vapor pressure of pure substance 2. Concentration Partial Pressure of A in solution PA = (PAo) x (NA) Total Pressure:  PA + PB = PAo NA + PBo NB

25. Boiling Point - Composition C1 has more % of A than B at its boiling temperature in liquid phase. Ideal mixture always has higher proportion of lower boiling in its vapor phase.

26. Dehydration Removing water molecule. Dehydration reactions are always reversible.

27. Dehydration Alcohol with ? hydrogen undergo a dehydration reaction. You need to have a catalyst. The product (alkene) has different boiling point from the reactant. Distillation also very useful to protect the irreversible reaction i.e. formation of product.

28. Dehydration Here is the equation of a dehydration reaction.

29. Procedure � Ist distillation Place 20 mL of 4 � methyl � 2- pentanol in 50 mL dry RB. Add 8 mL of cold 9 M sulfuric acid. Mix it thoroughly. Set up fractional distillation apparatus. Slowly heat the mixture to boiling. Maintain the temperature at 55 � 77 ?C.

30. Procedure � Ist distillation Do not allow the temperature raise above 90 ?C. Continue the distillation until only 8 mL of liquid remains in the RB. Transfer the distillate to a separatory funnel and wash it with 5 % aq. Sodium bicarbonate solution and water. Dry the organic layer with anhydrous CaCl2.

31. Procedure � IInd distillation Set up a simple distillation apparatus using dry 50 mL RB. Weigh a dry 50 mL RB and use as a receiver. Distill the dry organic layer. Collect the liquid fraction from 70 � 90 ?C. Tightly close the RB.

32. GC � MS Generally compounds used to inject one end. The Carrier gas take the sample down to the column. The analyte (A-B-C) undergoing ionization and fragmentation The charged fragments (A+ B+ C+) being separated by mass.

33. GC � MS Take one or two drop of the final distillate using a dry eye � dropper. Dilute it with diethyl ether. Record its GC MS spectrum and analyze it.

34. Notes Dilute the sulfuric acid carefully. Release the pressure often when you use separatory funnel. Do not forget to add boil seizers when you do distillation.

35. Notes Apply greases to joints. Use ice bath when you collect. Work in pairs Ask before you Act!!!