Experiment 22:

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Experiment 22

• THE SOLVENTLESS ALDOL-TYPE CONDENSATION

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Objectives

• To synthesize an a,b unsaturated ketone from an
  aldehyde and a ketone using solvent-free
  conditions.
• To purify the product through a
  recrystallization.
• To identify and analyze purity through TLC and
  melting point analysis.
• To analyze the product using IR spectra.

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Before coming to lab

• Review these techniques
• Recrystallization
• TLC Analysis
• Melting Point Analysis

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ALDOL CONDENSATIONS

• Aldol condensations are nucleophilic additions of
  an enolate ion, which are strong nucleophiles, to
  another CO group under basic conditions.
• Protonation gives the aldol product.
• Once formed, the aldol product undergoes
  dehydration in base.
• Abstraction of an a proton gives an enolate that
  can expel an OH ion to give a conjugated
  product.
• Dehydration is usually exothermic because it
  leads to a very stable conjugated product.

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CHEMICAL EQUATION
3,4-dimethoxy benzaldehyde
1-indanone
Aldol Product
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MECHANISM
Base removes a proton to form enolate ion.
Resonance stabilized enolate forms carbanion,
which attacks CO of aldehyde
Oxygen anion removes proton from water, releasing
OH.
When new C-C bond forms, CO p bond breaks,
electrons stay with oxygen.
Acidic a proton is removed by OH. Electrons
form new p bond.
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TYPICAL ALDOL CONDENSATION

• A typical aldol condensation reaction is carried
  out in an organic solvent, such as ethanol,
  requiring eventual waste disposal.
• Isolation of the product requires a much more
  involved work up, not to mention the hazards to
  the experimenter and the environment due to waste
  disposal.
• Another challenge is that solution phase reaction
  is reversible, so low product yields may result.

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GREEN CHEMISTRY CONCERNS

• One of the main themes of greener chemistry is to
  cut down on the use of solvent, and hence cut
  down on solvent waste. The best way to do this
  is simply not to use any solvent at all.
• Workup is generally easier since as the reaction
  proceeds, the product separates from the melt as
  a solid, making work up much less complicated.
• Another benefit is that unlike a solution phase
  reaction, the solid-state reaction is
  irreversible, resulting in higher chemical
  yields.

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OVERVIEW

• Synthesize aldol product in test tube.
• Recrystallize solid in propanol/water to purify.
• Suction filter to isolate solid.
• Dry product in oven.
• Obtain product mass, calculate yield, do
  melting point analysis.

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EXPERIMENTAL PROCEDURE(Synthesis)

• Place aldehyde and ketone in large test tube.
• Crush solids with glass rod until liquefied.
• Add NaOH. Mix and scrape sides of test tube
  until pale green solid forms.
• Continue to react for 15 minutes at room
  temperature.

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EXPERIMENTAL PROCEDURE(Purification and Product
Isolation)

• Place test tube in a 90oC water bath.
• Add 9010 PROPANOL/WATER and heat until solid
  dissolves.
• Suction filter.
• Transfer solid to PREWEIGHED WATCH GLASS AND
  PLACE IN OVEN 15 MINUTES to dry.
• Obtain final product mass and calculate yield.
• Proceed to PRODUCT ANALYSIS (TLC, mp, IR).

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Table 22.1
Theoretical yield (g) Determine limiting reagent first, then calculate theoretical yield. HINT Dont round too soon!
Actual yield (g)
yield
Melting range (oC) Start temperature dial on setting of 5. Back down one tic mark 150oC and watch closely. Record Ti-Tf range. Compare to literature value to determine purity of product.
Product Appearance Record the physical state and color of product.
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Table 22.4
Atom Economy () Calculate based on reactants ONLY! Review Experiment 13 for calculation.
Experimental Atom Economy () Calculate based on reactants ONLY! Review Experiment 13 for calculation.
Eproduct Review Experiment 13 for calculation.
Cost Per Synthesis () Costs of stock bottles of compounds on p. 192. Remember to use reactants and catalyst in this calculation!
Cost per Gram (/g) CPS/actual yield (g)
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Table 22.2
Compound TLC Rf values TLC Rf values
Compound Standard Sample
1-indanone Rf values are UNITLESS! Rf values are 2 decimal places ONLY! Rf values are UNITLESS! Rf values are 2 decimal places ONLY!
3,4-dimethoxybenzaldehyde Rf values are UNITLESS! Rf values are 2 decimal places ONLY! Rf values are UNITLESS! Rf values are 2 decimal places ONLY!
Aldol Product Rf values are UNITLESS! Rf values are 2 decimal places ONLY! Rf values are UNITLESS! Rf values are 2 decimal places ONLY!
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Product Analysis(IR)
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Table 22.3
Functional Group Base Values (cm-1) 1-Indanone 1-Indanone 3,4-dimethoxy -benzaldehyde 3,4-dimethoxy -benzaldehyde Aldol Product Aldol Product
Functional Group Base Values (cm-1) Frequency (cm-1) Frequency (cm-1) Frequency (cm-1) Frequency (cm-1) Frequency (cm-1) Frequency (cm-1)
sp3 CH stretch 2800-3000
sp2 CH stretch 3000-3100
CO stretch 1680-1740
C-O stretch 1000-1200
aromatic CC stretch (2) 1500-1600
aldehyde CH stretch (2) 2700-2800
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SAFETY CONCERNS

• Solid NaOH is very corrosive! Immediately flush
  skin with water if any gets on your skin!
• Propanol is very flammable! Use extreme caution
  during purification!

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WASTE MANAGEMENT

• Place all liquid waste in container labeled
  LIQUID ORGANIC WASTE.
• Place all solid waste in container labeled SOLID
  WASTE.
• Place all used TLC capillaries and melting point
  capillaries in broken glass container, NOT
  TRASHCAN!
• Leave TLC chambers with lids off in your lab
  drawer.

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CLEANING

• Clean all glassware with soap, water, and brush,
  followed by a rinse with wash acetone before
  returning to lab drawer.
• DO NOT return any glassware to lab drawer dirty
  or wet!

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LABORATORY NOTEBOOK(Pre-lab)

• OBJECTIVE (Must clearly state)
• What compounds will be made and how
• How the compounds will be purified
• How the purity of the product will be determined
• CHEMICAL EQUATION
• Include the chemical equation from the top of
  page 185.
• TABLE OF PHYSICAL DATA (Complete the following
  table using a site listed on WWW Links ONLY.
  Wikipedia is unacceptable!)
• REFERENCE TO PROCEDURE (Must include)
• full title including edition and author names
• page numbers where actual procedure can be
  found

Compound MW (g/mol) mp(oC) bp(oC) d (g/mL) HAZARDS
3,4-dimethoxybenzaldehyde X X
1-indanone X X
Sodium hydroxide X X
1-propanol X
Diethyl ether X
hexane X
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LABORATORY NOTEBOOK(In-lab)

• DATA/CALCULATIONS
• Initial weights of 1-indanone and
  3,4-dimethoxybenzaldehyde used
• Weights of filter paper and watch glass
• Weight of watch glass filter product
• Final weight of dry product
• Physical state and color of product
• Theoretical yield calculation
• yield calculation
• TLC diagram including all cm measurements
• Atom economy calculation
• Experimental atom economy calculation
• Eproduct calculation
• Cost per synthesis and cost per gram calculations
• EXPERIMENTAL PROCEDURE
• In paragraph form, BRIEFLY describe the procedure
  that you actually followed during the lab.
• Paragraph must be written in PAST TENSE, PASSIVE
  VOICE.
• Include any volumes or weights of chemicals used
  during the experiment.
• Include any mistakes, accidents or observations
  if applicable.