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

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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

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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

Distillation & Boiling Point

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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

fractionaldistillation data

• Compare simple and fractional distillations

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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).

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QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Steam Distillation Set-Up

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Day One or Day Two:

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 to1 week.

Measure the distance ofinhibition

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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.

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GC-MS DataPossible compounds in the oils:

OH

OCH3

EugenolFW = 164

bp = 254°C

CaryophylleneFW = 204

bp = 262-264°C

O

Ar-TumeroneFW = 216

O

TumeroneFW = 218O

O

O

OCH3OCH3

H3CO OCH3

Allyl methoxybenzodioxoleFW = 192

Allyl trimethoxybenzeneFW = 208

CurloneFW = 218

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Nutmeg Oil GC-MS Data



Gas chromatogram of Nutmeg oil

Two major compounds:A & B

Note retention times &Relative abundances:

A is 14.14 minutes, 100%B is 14.49 minutes, 40%

Most likely, B has a higher bpand/or FW than A.

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Mass Spectrum of A

M+ at 192

Compound is:



O

O

OCH3

Allyl methoxybenzodioxoleFW = 192

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Mass Spectrum of B

M+ at 208

Compound is:


are needed to see this picture.OCH3

H3CO OCH3

Allyl trimethoxybenzeneFW = 208

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Steam Distillation: Natural Product Isolation

Steam distillation of citral from lemon grass oil

Citral (oil) comprised of:

H3C

CH3 CH3

CHO

Geranial

H3C

CH3 CH3

CHONeral

Uses of citral:• Defense pheromone for ants• In perfumes for lemon-like scent• Precursor to vitamin A

CH3H3C

CH3

CH3 CH3

OH

Vitamin A

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Day Two:

Procedure 3: A microscale distillation of a 50:50 unknown, two-component 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 confirmidentities.

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!!!**

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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

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Procedure 4:

1. Adjust bp for pressure:Add (or subtract) 0.5°C for every10 Torr the lab’s atom. pressure is below (or above) 760 Torr.

2. Plot data usingExcel. Be sure to superimpose both sets ofdata on one graph. Should end up with 2 curveson one graph.

3. Compare simple vs.fractional distillations.

4. Which of the two achievesthe best separation of liquids?

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Simple vs. Fractional

Prediction:Fractional distillation is a more effective purification technique than simple distillation.

An example Excel graph with two data sets superimposed:


are needed to see this picture.Simple distillation

Fractional distillation

A two-componentmixture:A & B

bp of pure B

bp of pure A

Drops of Distillate

Tem

pera

ture

(°C

)

Documents

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