Experiment 20

1
Experiment 20

• CHEMOSELECTIVE REDUCTION WITH NaBH4

2
Objectives

• To synthesize vanillin acetate by acetylation of
  p-vanillin, then to perform a chemoselective
  reduction using NaBH4.
• To use TLC to follow the course of the reaction.
• To analyze the purity of products using TLC,
  HPLC and melting point analysis.
• To characterize the reactants and products using
  1H-NMR and IR spectroscopy.

3
Before coming to lab

• Review these techniques
• Vacuum filtration
• TLC Analysis
• HPLC analysis
• Melting point analysis
• Extraction

4
CHEMICAL EQUATION(Acetylation)
5
MECHANISM(Acetylation)
6
OVERVIEW(Part 1)

• Synthesize vanillin acetate.
• Isolate solid product using vacuum filtration, or
  oily product by extraction.
• Prepare HPLC sample of pure product and submit
  for analysis.
• Perform TLC experiment on pure product.
• Secure product and allow to dry until next lab
  period.

7
SYNTHESIS(Preparation of Vanillin Acetate)

• Mix p-vanillin and aqueous NaOH in flask with
  stir bar.
• Add ice, then acetic anhydride drop wise.
• Cover loosely with cork, then stir 15 minutes.

125 mL
8
PURIFICATION(Preparation of Vanillin Acetate)

• If a white solid forms
• Suction filter
• Recrystallize with ethanol
• Cool to room temp, then in ice bath
• Suction filter again
• Prepare HPLC and TLC samples (LABEL CLEARLY!)
• Submit solid product to instructor to dry until
  next lab period.

9
PURIFICATION(Preparation of Vanillin Acetate)

• If an oil forms
• Transfer to separatory funnel and extract 2X with
  ethyl acetate.
• Wash organic layer with aqueous NaOH and check
  pH.
• Dry over MgSO4.
• Evaporate solvent.
• Prepare HPLC and TLC samples (LABEL CLEARLY!)
• Submit solid product to instructor to dry until
  next lab period.

10
Tables 20.1 and 20.3
Theoretical yield (g) Calculated DAY 1 based on limiting reagent
Actual yield (g) Obtained DAY 2 after product has dried
Percent yield Calculated DAY 2
Product Appearance Recorded DAY 1
Experimental Melting Point (oC) Performed DAY 2must record Ti-Tf range!
Atom Economy () Calculated DAY 1
Experimental Atom Economy () Calculated DAY 1
Eproduct Calculated DAY 2
Cost per synthesis () Calculated DAY 1
Cost per gram (/g) Calculated DAY 2
11
SAFETY

• Acetic anhydride and NaOH are both corrosive!
• Ethanol is highly flammable!

12
WASTE

• LIQUID WASTE Place liquid filtrate from vacuum
  filtration in this container.

13
CHEMICAL EQUATION(Reduction)
NOTE Stoichiometry for this reaction is 41.
This means that 1 mole of NaBH4 can reduce 4
moles of carbonyl compound, to produce 4 moles of
the product.
14
REDUCING AGENTS

• Reducing agents cause a reaction resulting in a
  product containing more bonds from carbon to
  hydrogen (or fewer bonds to oxygen).
• NaBH4 (sodium borohydride) is a versatile and
  useful reducing agent in organic chemistry,
  however will only reduce carbonyl groups of
  aldehydes and ketones.
• LAH (lithium aluminum hydride) is another common
  reducing agent, however use of this reducing
  agent will result in the reduction of many other
  carbonyl containing compounds, including esters,
  carboxylic acids and amides.

15
MECHANISM(Reduction)
16
OVERVIEW(Part 2)

• Reweigh ACYLATION PRODUCT, perform melting point
  analysis.
• Cool, then react with NaBH4 in ethanol.
• TLC _at_ 30min to determine reaction progress.
• If complete, transfer to sep funnel.
• Perform extraction, dry organic layer.
• Evaporate solvent, obtain product mass.
• Submit HPLC samples for analysis.
• Perform final TLC analysis and stain in 2,4-DNP.

17
SYNTHESIS(Reduction)

• Reweigh solid product from previous lab,
  calculate yield, and obtain mp.
• Transfer solid to flask w/stir bar and dissolve
  in ethanol.
• Cool in ice bath, then slowly add NaBH4 while
  stirring.
• Stir at 0oC for 15 min, then 15 min more at RT.
• Perform TLC experiment to determine reaction
  progress.
• If complete, add 10 mL water and stir 5 minutes.

50 mL
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PURIFICATION(Reduction)

• Transfer reaction solution to separatory funnel.
• Extract 2X with diethyl ether.
• Wash with water and brine.
• Dry organic layer over MgSO4.
• Decant liquid ONLY into tared flask and evaporate
  solvent.
• Obtain product mass calculate yield.
• Prepare HPLC and TLC samples.

19
Tables 20.2 and 20.4
Theoretical yield (g) Calculated based on DAY 1 product
Actual yield (g) Obtained NEXT LAB
Percent yield Calculated NEXT LAB
Product Appearance Recorded on DAY 2
Atom Economy () Calculated DAY 2
Experimental Atom Economy () Calculated DAY 2
Eproduct Calculated NEXT LAB
Cost per synthesis () Calculated DAY 2
Cost per gram (/g) Calculated NEXT LAB
20
PRODUCT ANALYSISHPLC

• HPLC Analysis
• Used at the end of the experiment to identify and
  quantify compounds present during the synthesis,
  as well as the purity of the final products from
  each step.
• Table 20.5

Compound Standard Sample Sample Sample Sample
Compound Standard ACYLATION PRODUCT ACYLATION PRODUCT PURE REDUCTION PRODUCT PURE REDUCTION PRODUCT
Compound Retention Times (min) Retention Times (min) Area Percent Retention Times (min) Area Percent
p-vanillin
Vanillin acetate
Vanillin alcohol
Vanillyl alcohol
21
PRODUCT ANALYSISTLC

• TLC Analysis
• Used to determine reaction progress during the
  course of the experiment, as well as to identify
  and determine purity of products at the end of
  the experiment.
• 2,4-DNP will be used as a stain to detect the
  presence/absence of the aldehyde functional
  group.
• Table 20.6

Compound TLC Rf values TLC Rf values TLC Diagram
Compound Standard Sample
p-vanillin
Vanillin acetate
Vanillin alcohol
Vanillyl alcohol
22
PRODUCT ANALYSISIR

• IR Analysis
• IR spectra of reactants and products can be used
  to determine the presence and absence of certain
  types of functional groups which indicate the
  conversion of one compound to another during the
  course of the synthesis.
• Table 20.7

Functional Group Base Values p-vanillin p-vanillin Vanillin acetate Vanillin acetate Vanillin alcohol Vanillin alcohol
Functional Group Frequency (cm-1) Frequency (cm-1) Frequency (cm-1) Frequency (cm-1) Frequency (cm-1) Frequency (cm-1) Frequency (cm-1)
OH stretch 3200-3600
C-O stretch 1000-1300
CO stretch 1680-1740
Aldehyde C-H stretch 2700-2800
23
PRODUCT ANALYSISNMR

• NMR Analysis
• 1H-NMR spectra of reactants and products can be
  used to determine the presence and absence of
  certain types of signals which indicate the
  conversion of one compound to another during the
  course of the synthesis.
• Table 20.8

p-vanillin Vanillin acetate Vanillin alcohol
24
SAFETY CONCERNS

• Ethanol, ethyl acetate, hexane, diethyl ether,
  and acetone are all FLAMMABLE materials.
• Sodium borohydride and 2,4-DNP are TOXIC in large
  concentrations.
• Sulfuric acid, used to prepare 2,4-DNP stain, is
  CORROSIVE.

25
WASTE MANAGEMENT

• SOLID WASTE Place all solid waste in this
  container including magnesium sulfate or any
  solid product.
• LIQUID WASTE Place all liquid waste into this
  container including filtrates and aqueous washes
  from extraction.
• GLASS WASTE Place used TLC and melting point
  capillary tubes in this container.
• PAPER WASTE Place any gloves, TLC plates,
  filter papers, paper towels, etc. in the yellow
  trashcan.

26
CLEANING

• Any glassware used to contain only volatile
  organic solvents can simply be rinsed with wash
  acetone.
• All other glassware should be cleaned with soap,
  water and brush, then rinsed with wash acetone or
  hand dried.

27
LABORATORY NOTEBOOK(Pre-lab)

• OBJECTIVE (Must clearly state)
• What compounds will be made and how
• What will be investigated with the compounds
• CHEMICAL EQUATION
• Include the general chemical equation from the
  top of page 169 from handout.
• TABLE OF PHYSICAL DATA (Complete the following
  table using a site listed on WWW Links ONLY.
  Wikipedia is unacceptable!)

Compound MW (g/mol) mp(oC) bp(oC) d (g/mL) HAZARDS
p-vanillin X X
Vanillin acetate X X
Vanillin alcohol 196.20 X X X irritant
Acetic anhydride X
Ethanol X
Ethyl acetate X
Acetone X
Hexane X
Diethyl ether X
Sodium borohydride X X
2,4-dintrophenylhydrazine X X
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LABORATORY NOTEBOOK(In-labPart 1)

• Synthesis Preparation of Vanillin Acetate
• Weight of p-vanillin used
• Weight of ice used
• Volume of 10 NaOH used
• Volume of acetic anhydride used
• Theoretical yield calculation
• Purification of Vanillin Acetate
• Volume ethanol used
• Weight of small filter
• Weight of watch glass
• HPLC vial slot of ACYLATION PRODUCT
• Weight of filter watch glass dry product
• Final product mass
• yield calculation
• Experimental melting point
• Atom economy calculation
• Experimental atom economy calculation
• Eproduct calculation
• Cost per synthesis calculation

29
LABORATORY NOTEBOOK(In-labPart 2)

• Synthesis Reduction of Vanillin Acetate
• Volume of ethanol used
• Weight of sodium borohydride used
• Sketch of TLC diagram (taken during experiment)
• Theoretical yield calculation (based on product
  mass from part 1!)
• Purification of Product Alcohol
• Volume of diethyl ether, deionized water, and
  NaCl used
• HPLC vial slot of PURE REDUCTION PRODUCT
• Weight of 50 mL flask
• Weight of flask product
• Final product mass
• yield, Atom economy, Experimental atom economy,
  Eproduct, Cost per synthesis, and Cost per gram
  calculations
• Sketch of TLC diagram (taken at end of
  experiment)

• 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.