1. CHEMOSELECTIVE REDUCTION WITH NaBH4
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. Experimental Melting Point (oC) Experimental Atom Economy (%)
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 2…must record Ti-Tf range!
Atom Economy (%)
Calculated DAY 1
Experimental Atom Economy (%)
“Eproduct”
Calculated DAY 2
Cost per synthesis ($)
Cost per gram ($/g)

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 4:1. 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.
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

18. 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. Experimental Atom Economy (%)
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 (%)
“Eproduct”
Calculated NEXT LAB
Cost per synthesis ($)
Cost per gram ($/g)

20. PRODUCT ANALYSIS—HPLC
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
ACYLATION PRODUCT
PURE REDUCTION PRODUCT
Retention
Times
(min)
Area Percent
Retention Times
p-vanillin
Vanillin acetate
Vanillin alcohol
Vanillyl alcohol

21. PRODUCT ANALYSIS—TLC 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 Diagram
Standard
Sample
p-vanillin
Vanillin acetate
Vanillin alcohol
Vanillyl alcohol

22. PRODUCT ANALYSIS—IR 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
Vanillin acetate
Vanillin alcohol
Frequency
(cm-1)
OH stretch
C-O stretch
C=O stretch
Aldehyde C-H stretch

23. PRODUCT ANALYSIS—NMR 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!)
REFERENCE TO PROCEDURE (Must include…)
full title including edition and author names
numbers where actual procedure can be found
Compound
MW (g/mol)
mp(oC)
bp(oC)
d (g/mL)
HAZARDS
p-vanillin X
Vanillin acetate
Vanillin alcohol
196.20
irritant
Acetic anhydride
Ethanol
Ethyl acetate
Acetone
Hexane
Diethyl ether
Sodium borohydride
2,4-dintrophenylhydrazine

28. LABORATORY NOTEBOOK (In-lab—Part 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
Cost per gram calculation

29. LABORATORY NOTEBOOK (In-lab—Part 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.