Transcript Molecular ion - Department of Chemistry

Experiments of Microscale
Organic Chemistry
1
Workshop for Secondary School Teachers
Dr. W M TSUI
Department of Chemistry, HKUST
Department of Chemistry
Outline
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Introduction of Microscale Organic Chemistry
Introduction of designing experimental procedures
Microscale Organic Glassware
Techniques in Microscale Organic Experiments:
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Solvent /Reagent Dispensing, Reaction Setup
Liquid-Liquid Extraction, Filtration
Purification methods
Characterization Method of Organic Compounds
Experiment highlights
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Organic synthesis & natural products synthesis
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Complex and fascinating molecular structures can be
assembled from simple starting materials.
Designed molecular frameworks containing carbon
atoms in combination with H, O, N, S, and halogens,
can be synthesized on demand and tested for various
applications.
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Organic synthesis & natural products synthesis
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These useful compounds range from biological tools
and medicines to high-value materials for cosmetics,
computers and useful devices
O
OH
NaOH
C
O
OH
OH
C
OH
(CH3CO)2O
O
CO2
C
O
CH3
aspirin
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Introduction of Microscale Organic Chemistry
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Had been gradually recognized and adopted at
secondary school level
Handle with small quantities of chemical substances
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Macroscale vs. Microscale
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Quantities of
chemicals
Glasswares
Cost per
experiment
Macroscale
Microscale
5-100 g
0.005-0.5 g
25 - 500 mL
Microscale kit
(<5mL)
$10-100
$100-1000
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Advantages
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1.
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Require smaller storage area
Save laboratory space
Reduce amount of chemical waste
Improve laboratory safety (smaller amount of …)
Shorter reaction time (efficient heat transfer…)
Save time for preparation and work up
More time for evaluation and communication
………….
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Microscale Organic Glassware
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Various designs
http://www.sigmaaldrich.com/labware/glassware-catalog/glassware-kits-microscale.html
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Microscale Organic Glassware
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All-purpose kit:
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Designing experimental procedures
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Stage 1: Setup reaction
 Experimental
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Stage 2: Isolation of crude product
 Solvent
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extraction, Filtration, Precipitation
Stage 3: Purification of crude product
 Distillation,
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setup, Temperature, Time, Catalyst, Solvent
Recrystallization, Sublimation
Stage 4: Characterization
 Melting
point, Boiling point, IR, MS
Technique:
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Transfer of reagent/dispensing of solvent
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Macroscale:
 Measuring
cylinder
 Beaker
 Conical
flask
 Dropping funnel
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Microscale:
 Syringe
 Needle
 Septum
1.0 mL Syringe
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Technique: Setup for Organic Synthesis
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Organic Synthesis:
Formation and
breaking of C-C bond,
C-O bond, C-H bond,
C-X bond, etc.
Reflux: for long
reaction time
Macroscale
reflux setup
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Technique: Microscale Experiment Setup
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Microscale Organic Synthesis:
Water condenser
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Microscale
Condenser, Threaded
Water out
Reagents (+ catalyst)
Anti-bumping granules
Microscale Round-Bottom
Flasks, Threaded
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Sand bath
Microscale
reflux setup
Water in
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Technique: Microscale Experiment Setup
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Microscale Organic Synthesis: Air condenser
Reagents (+ catalyst)
Anti-bumping granules
Microscale RoundBottom Flasks,
Threaded
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Microscale reflux setup
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Isolation Technique: Filtration
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Vacuum filtration:
 Probably the most common
type of filtration used by
chemists. The funnel used
for this method is called
Hirsch funnel. This funnel
has a flat disc inside which
is made from porous
ceramic materials
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Isolation Technique: Filtration
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Pipette filtration:
 For small quantity of
crystals
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Isolation Technique: Liquid-liquid Extraction
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Partition coefficient
Solubility in solvents
Screw cap
Test tube
Separatory
funnel
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Purification Technique: Distillation
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For liquids with various volatilities
Macroscale distillation setup
Microscale distillation setup
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Purification Technique: Sublimation
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For solids
Macroscale sublimation setup
Microscale sublimation setup
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Purification Technique: Recrystallization
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For solids
Various Solubility
Temperature
controlled by
depth in sand
Microscale
5mL
Reaction tube
Macroscale
250mL
Conical flask
Microscale
5mL
Conical flask
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Purification Technique: Recrystallization
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Steps in Recrystallization:
Dissolution (various choice of Solvent)
Hot Filtration
Decolorization
Crystallization
Collection
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Purification Technique: Recrystallization
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The general idea is to follow the “like dissolves like”
principle, e.g. compounds containing hydroxyl groups
are best recrystallized from hydroxy-containing solvents
Class of compound
Suggested solvents
Hydrocarbons
Light petroleum, pentane, cyclohexane and
toluene
Ethers
Diethyl ether and dichloromethane
Halides
Dichloromethane
Carbonyl compounds
Ethyl acetate and acetone
Alcohols, acids
Salts
Ethanol
Water
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Methods for crystallization
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2
Ice bath
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Purification Technique: Recrystallization
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Crystallization
Slow cooling: the easiest method and works for most cases
Scratching: induced crystallization by scratching the inside
of the beaker or flask with a glass stirring rod. This will
produce microscopic fragments of glass that may act as
surfaces on which crystal growth can begin
Seeding: taking a small crystal from the original solid or
the other groups and dropping them into the solution
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Characterization of organic compound
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Melting point / melting
point apparatus
 Simplest
and most common
characterization method
for solid organic
compounds
 Purity check
 Affordable
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Characterization of organic compound
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Boiling point / distillation
apparatus
 Simplest
and most common
characterization method for
liquid organic compounds
 Purity check
 Affordable
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Characterization of organic compound
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Infrared spectrum
Infrared
spectrophotometer
 Absorption of infrared
electromagnetic radiation
 Information of functional
groups
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Characterization of organic compound
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To allow passage of IR, most sample cuvettes
have mineral salt windows [Caution! Avoid
high humidity.]
Transmission limit:
– NaCl
650cm-1
– KBr
350cm-1
– CsI
56 μm (200cm-1)
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Characterization of organic compound
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Bond
Base Value
Strength / Shape Comments
1
C=O
1715
s, "finger"
Exact position depends on type of carbonyl
2
O-H
3600
s, broad
Broad due to hydrogen bonding
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N-H
3500
m
Can tell primary from secondary
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C-O
1100
s
Also check for O–H and C=O
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C=C
1650
w alkene
m-s aromatic
Alkene w due to low polarity
Aromatic usually in pairs
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CΞC
2150
w, sharp
Most obvious in terminal alkynes
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C-H
3000
s
As hybridisation of C changes sp3-sp2-sp,
the frequency increases
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CΞN
2250
m, sharp
Characteristic since little else around this
value
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Characterization of organic compound
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Functional groups can be identified
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Infrared spectrum of acetone
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Characterization of organic compound
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Mass spectrum / mass spectrometer
mass-to-charge ratio of molecular ion
Picture from http://www.mhhe.com/physsci/chemistry/carey/student/olc/ch13ms.html
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Characterization of organic compound
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Mass-to-charge ratio:
 Molecular
ion
 Fragmentation pattern of
molecular ion
Molecular ion
The ion obtained by the loss of an electron from
the molecule
M+
Symbol often given to the molecular ion
Radical cation
+ve charged species with an odd number of
electrons
Fragment ions
Lighter cations formed by the decomposition of
the molecular ion.
These often correspond to stable carbcations.
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Characterization of organic compound
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Decane (C10H22)
Molecular ion at
m/z = 142
142-29 = 113
113-14 = 99
etc
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Characterization of organic compound
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Acetone (C3H6O)
Molecular ion at m/z = 58
O
H3C
C
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CH3
–15
–28
15
58
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Experiment 1:
Microscale separation of components in a mixture
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3 components
caffeine
p-dimethoxybenzene
acetaminophen
Separation based on their different
physical and chemical properties
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Experiment 1:
Microscale separation of components in a mixture
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Step 1: Solubility test
 Technique:
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Solid-liquid extraction (Filtration)
Step 2: Acid-base chemistry
 Technique:
Liquid-liquid extraction, Pipette filtration,
Evaporation
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Step 3: Purity check
 Technique:
TLC analysis
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Experiment 1:
Microscale separation of components in a mixture
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Step 1: Solubility test
 water,
dichloromethane, hexane
soluble
Insoluble
Powder
Slightly soluble
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Experiment 1:
Microscale separation of components in a mixture
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Solid-liquid extraction (Filtration)
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Experiment 1:
Microscale separation of components in a mixture
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Step 2: Acid-base chemistry
basic
neutral
HCl
org
NaOH
aq
org
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Experiment 1:
Microscale separation of components in a mixture
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Liquid-liquid extraction
 Release
pressure
 Which layer on the top?
 Test by adding water
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Experiment 1:
Microscale separation of components in a mixture
Some water will be
transferred into the
organic phase because
of the partial miscibility
of the organic phase and
water  Organic
solution contaminated
with traces of water.
pdimethoxybenzene
aqueous
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organic
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Sodium
chloride
Diethyl ether
Water
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brine works to pull the
water from the organic
layer to the water layer
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Experiment 1:
Microscale separation of components in a mixture
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Dry by anhydrous Na2SO4 (Preliminary purification)
Pipette filtration
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Experiment 1:
Microscale separation of components in a mixture
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Evaporation
Needle
Compressed
air
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Experiment 1:
Microscale separation of components in a mixture
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Step 3: Purity check
 Thin
layer chromatography (TLC)
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Experiment 1:
Microscale separation of components in a mixture
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Thin layer chromatography (TLC)
Chromatography:
Separation of compounds by the
distribution between two phases –
Mobile phase & Stationary phase
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Experiment 1:
Microscale separation of components in a mixture
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stationary
phase
(TLC plate:
Silica gel)
Sample mixture
mobile phase (solvent)
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Experiment 1:
Microscale separation of components in a mixture
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Department of Chemistry
Experiment 2:
Catalytic Hydrogenation of Methyl Oleate
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Organic Synthesis by Hydrogenation
 Microscale Experiment Setup
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methyl oleate
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H2(g)
Catalyst: Pd/C
methyl stearate
Reagents:
 Methyl
oleate, H2, Palladium on charcoal, Methanol
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Catalytic Hydrogenation of Methyl Oleate
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Syringe instead of
dropping funnel
Setup:
 Generation
of hydrogen
gas as reagent
H2(g)
of septum
 Use of needles
 Use of syringe
HCl(aq)
 Use
Zn metal in
5mL flask
5mL flask
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Catalytic Hydrogenation of Methyl Oleate
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Collect H2
into a
inverted
measuring
cylinder
H2(g)
Syringe instead of
dropping funnel
HCl(aq)
Zn metal in
5mL flask
5mL flask
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Catalytic Hydrogenation of Methyl Oleate
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Beginning of
synthetic reaction
Use of syringe
+ needle
H2(g)
Methyl oleate
+ methanol
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Catalytic Hydrogenation of Methyl Oleate
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Use of parafilm to
prevent leakage
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Catalytic Hydrogenation of Methyl Oleate
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Workup:
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Filter off Pd/C
Evaporate excess CH3OH
Purification of methyl stearate
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Isolation of second crop of product (by adding H2O to
filtrate)
Characterization
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Melting point determination