Lecture 4 Chem 237 Feb 10 2015 This Week Start Experiment 2 Preparation of Synthetic Banana Oil Isoamyl Acetate Purify product simple distillation NMR and IR analysis Preparation of Synthetic Banana Oil Isoamyl acetate Shift equilibrium by removal of water Driving an Equilibrium by H2O Removal Dean Stark tube apparatus water collects here mark level Fractional Distillation Doing Multiple Distillations with One Column fractional distillation a b 20 1 100 oC a b 10 1 120 oC a b 3 1 a b 1 1 140 oC 160 oC Refer to your lab manual for pictures instructions pp 53 55 Fractional Distillation Columns eg if a column can achieve same as 5 simple distillations the column is said to have 5 theoretical plates Height Equivalent to Theoretical Plate HETP length theoretical plates Vigreux Widmer Glass beads Most laboratory columns have 2 15 theor plates Fractional Distillation Issues Why not use packed columns to maximize theoretical plates Several Problems 1 Low throughput 2 Hold up loss of material on large surface area 3 Non ideal liquid vapor equilibrium in column flooding Type Description Throughput mL min Hold up mL plate HETP cm Vigreux tube with indentations 10 1 10 Metal sponge packed tube filled with stainless steel sponge 5 1 5 Glass helices 1 8 glass helices 2 8 0 8 3 4 Widmer see picture 1 2 0 4 2 Distillation Separation of a mixture of liquids based on different vapor pressures of the components Vapor pressure of pure A PA0 liquid A Dalton s Law P PA PB When P Pair solution boils Raoult s Law PA partial pressure of A PA XAPA0 XA mole fraction of A in liquid liquids A B If we distill a mixture of A B what is the composition of the distillate Relative Volatility What is the composition of the vapor in distillations YA mole fraction of A in vapor YA YB XAPAo XBPBo XA XB Suppose 1 1 mixture of A B in liquid and 9 XA XB 0 5 A more volatile than B after 1 distillation YA 9 YB vapor is 90 pure A Single distillation is only useful if 20 b p 80 oC How can we readily tell the composition of vapor How do we purify liquids with 20 Phase Diagrams Vapor Composition Acetone Benzene Vapor has this composition Vapor line Liquid line 62 C Liquid boils here 0 31 If Acetone Benzene 1 1 phase transition boiling occurs at 62 C 69 Acetone vapor composition at 31 Benzene or 62 C is Can t purify by simple distillation Phase Diagrams Vapor Composition Large VS Small Large Small Simple vs Multiple Distillations Fractional Distillation Vapor line Liquid line Plate 1 Plate 2 Plate 3 Plate 4 The more plates in a distillation the more the condensate becomes enriched in the more volatile component Non Ideal Mixtures may have unusual phase diagrams lower Minimum Boiling Azeotrope Boiling point of the mixture is than either pure compound 1st thing to distill Azeotrope is the Once the smaller component is depleted 2nd Compound Pure distills Can only get ONE compound pure Non Ideal Mixtures may have unusual phase diagrams higher Maximum Boiling Azeotrope Boiling point of the mixture is than either pure compound 1st Compound Pure 2nd Compound Azeotrope Can only get ONE compound pure Identification of Organic Compounds Absorption spectroscopy Infrared spectroscopy Ultraviolet and visible spectroscopy NMR spectroscopy spectral data molecular structure Absorption Spectroscopy Molecules absorb energy in the form of electromagnetic radiation when the energy difference between two states E is perfectly matched to the energy of the radiation Excited state E Ground state 0 Condition for absorption hc E h photon of energy h 0 h 9 537 x 10 14 kcal s mol 1 c 3 0 x 108 m s 1 frequency wavelength Electromagnetic Spectrum and Molecular Spectroscopy states involved nuclear spin states vibrational states electronic states energy region radio frequency infrared frequency UV visible Type of spectroscopy NMR IR UV vis Electromagnetic Spectrum and Molecular Spectroscopy Infrared spectroscopy is diagnostic of functional groups the molecule s Infrared Spectroscopy Identification of Functional Groups translate rotate and vibrate Molecules are not static they molecular vibrations IR spectroscopy measures Molecular vibrations can be though of as harmonic oscillations like a spring a b Hooke s Law for harmonic oscillation kf 2 c 1 2 ma mb mamb strength of bond depends on kf stronger bond higher masses of atoms depends on heavier atoms lower Bond H0 kcal mol C H 105 cm 1 3 000 C D 105 2 100 C C 90 1 200 C C 173 1 600 C C 229 2 200 wavenumber 1 These s can be probed with infrared light Intensity of absorption depends on the change in dipole moment larger stretch contract R2C O large strong IR signal smaller When there is little or no little or no IR signal is observed CH3 H3CC CCH3 H3C O C O symmetric stretch IR inactive These are termed vibrations A given functional group will absorb IR radiation at characteristic s 100 Transmittance X H 0 4000 3000 X Y X Y 2000 4 000 1 600 cm 1 is where most diagnostic stretching occurs X Y 1500 1000 600 cm 1 Fingerprint Region 1 600 600 cm 1 is called the It is a complex mixture of stretching and bending unique vibrations and is to each compound Molecular Vibrations can be Probed with IR light vibrational excited state Infrared Source E hc vibrational ground state Transmitted Beam IT Incident Beam Io sample At certain IT I0 because molecules have absorbed photons Transmittance T IT x 100 I0 Preparing samples salt plates Nujol mull solids ground into thin paste CDCl3 solution solids or oils KBr Pellet good for solids Film oil placed between plates Acid C O stretch at 1712 cm 1 Ester C O stretch at 1743 cm 1 Alkyl C H stretch 3 000 cm 1 Two N H stretches 3 000 cm 1 Broad O H stretch carboxylic acid Alkenyl C C at 1 661 cm 1 Alkenyl C H stretch 3 000 cm 1 Terminal alkene C H bend at 888 cm 1 CD3Cl CH3Cl Effect of Increased Mass on IR Spectrum C D stretch C H stretch C H bend C D bend Example of IR spectrum assignments Note this spectrum does not have Nujol Wavenumber cm 1 assignment intensity 3424 3346 NH2 N H stretch m 3225 Phenyl C H stretch w 2986 2900 Ethyl C H stretch w 1687 Ester C O stretch s 1282 Ester C O stretch s IR of Isoamyl Acetate O OH HO O O