Lecture 7. Ch 6: Distillation & Boiling Points. This Week In Lab: Ch 5: Extraction, Procedure 2 Ch 4 Final Report Due

Transcription

1 Lecture 7 Ch 6: Distillation & Boiling Points This Week In Lab: Ch 5: Extraction, Procedure 2 Ch 4 Final Report Due Next Week in Lab: Ch 6 PreLab due Ch 6: Procedure 1 & Procedure 2 (if time) Quiz 3 1

2 Distillation & Boiling Point Distillation: Purification technique Used to separate components of a liquid mixture or to purify an impure liquid Several basic types/variations: Simple distillation Fractional distillation Simple, high vacuum distillation Steam distillation - used to co-distill compounds with water Boiling Point: Physical property of a compound Used to identify an unknown 2

3 The Distillation Experiment: Ch 6 A two-day lab Day One: Procedures 1 & 2 Steam distillation of a spice Bioassay of spice oil to assess antibacterial property of oil Analyze GC-MS data of spice oil Day Two: Procedure 3 Microscale fractional distillation of an unknown mixture Identify the two components of the mixture via boiling point & solubility tests Outside of Lab Time: Procedure 4 Work with two data sets: simple distillation data and fractional distillation data Compare simple and fractional distillations 3

4 The Distillation Experiment: Ch 6 Day One: Steam distillation of a spice (Procedure 1): Choose a spice: clove, tumeric or nutmeg Build the steam distillation set-up: see Figure 6.3 Spice oils will co-distill with water! Each oil will contain at least two main compounds. Extract oil from water using dichloromethane (same technique used in extraction of caffeine). 4

5 Steam Distillation Set-Up 5

6 Day One or Day Two: The Distillation Experiment: Ch 6 Bioassay of spice oil (Procedure 2): Use prepared sterile agar plates Inoculate plates with a Bacillus cereus solution. Share an agar plate with your hood mate! Observe any inhibition of bacterial growth around the spice oil. Assess results after 24 hrs to 1 week. Measure the distance of inhibition 6

7 GC-MS Data You will be given the GC-MS data for your spice oil. Look at the GC chromatogram: Look at the number of major signals (25% relative abundance or higher). The number of major signals = the number of main compounds in the oil. Look at the retention times. In general, the higher the retention time, the higher the boiling point/fw of that compound. Look at the mass spectrum: Look for M + (molecular ion peak); M + equals the FW for that compound. You will determine the identities of the compounds in your oil by looking at the list of possibilities. 7

8 GC-MS Data Possible compounds in the oils: OH OCH 3 OCH 3 OCH 3 O H 3 CO OCH 3 O Allyl methoxybenzodioxole FW = 192 Eugenol FW = 164 bp = 254 C O Allyl trimethoxybenzene FW = 208 Ar-Tumerone FW = 216 O O Tumerone FW = 218 Caryophyllene FW = 204 bp = C Curlone FW = 218 8

9 Nutmeg Oil GC-MS Data Gas chromatogram of Nutmeg oil Two major compounds: A & B Note retention times & Relative abundances: A is minutes, 100% B is minutes, 40% Most likely, B has a higher bp and/or FW than A. 9

10 Nutmeg Oil GC-MS Data Mass Spectrum of A M + at 192 Compound is: OCH 3 O O Allyl methoxybenzodioxole FW =

11 Nutmeg Oil GC-MS Data Mass Spectrum of B M + at 208 Compound is: OCH 3 H 3 CO OCH 3 Allyl trimethoxybenzene FW =

12 Steam Distillation: Natural Product Isolation Steam distillation of citral from lemon grass oil Citral (oil) comprised of: CH 3 CH 3 CHO H 3 C Geranial CH 3 CH 3 H 3 C Neral CHO Uses of citral: Defense pheromone for ants In perfumes for lemon-like scent Precursor to vitamin A H 3 C CH 3 CH 3 CH 3 CH 3 Vitamin A OH 12

13 The Distillation Experiment: Ch 6 Day Two: Procedure 3: A microscale distillation of a 50:50 unknown, twocomponent mixture. Based on the observed boiling point data, determine the identities of the two components in your unknown mixture. Graph data in Excel. Be sure to correct the bp s for the lab s atmospheric pressure! Adjust bp for pressure: Add (or subtract) 0.5 C for every 10 Torr the lab s atmospheric pressure is below (or above) 760 Torr. Typo in page 164 s sample calculation!! Also, do solubility tests on each of the purified liquids to confirm identities. Possible unknowns: acetone, methanol, hexane, t-butanol, water, toluene, 1-butanol **Insulate your set-up with glass wool and be sure to use the correct column (distilling column) from your microscale kit!!!** 13

14 Simple vs. Fractional Simple Distillation: Used to separate mixture into pure components Works best if components boiling points differ by at least 75 C Fractional Distillation: To be used when components boiling points are closer together Unlike simple, uses a fractioning column; this column may be packed with material so as to increase the surface area for heat exchange, thus increasing the number of theoretical plates. The more theoretical plates, the better the purification/separation. Theoretical Plate: one cycle of vaporization and condensation 14

15 Procedure 4: 1. Adjust bp for pressure: Add (or subtract) 0.5 C for every 10 Torr the lab s atom. pressure is below (or above) 760 Torr. 2. Plot data using Excel. Be sure to superimpose both sets of data on one graph. Should end up with 2 curves on one graph. 3. Compare simple vs. fractional distillations. 4. Which of the two achieves the best separation of liquids? 15

16 Simple vs. Fractional Prediction: Fractional distillation is a more effective purification technique than simple distillation. An example Excel graph with two data sets superimposed: bp of pure B A twocomponent mixture: A & B Temperature ( C) Simple distillation Fractional distillation bp of pure A Drops of Distillate 16