Sodium Borohydride Reduction of Vanillin
Goal:
To reduce the aldehyde function of vanillin to a primary alcohol using
sodium borohydride in basic aqueous media.
O
H
HO
OH
NaBH4
0.01 M NaOH
OCH3
vanillin
Materials:
ring stand and clamp
magnetic stir bar and stirrer
sodium borohydride
TLC plates/developing chamber
3M HCl
ethyl acetate
small Petri dish
HO
OCH3
vanillyl alcohol
50 mL round bottom flask
vanillin
0.01M NaOH solution
I2/silica chamber
125 mL separatory funnel
sodium sulfate
Procedure: Obtain a 50 mL round bottom flask from the stockroom. Set up the ring
stand, clamp and stirrer to perform the reaction. Weigh approximately 1.0 g of vanillin,
record the mass in the laboratory notebook and add the solid to the round bottom flask
along with the magnetic stir bar. Add approximately 15.0 mL of 0.01M NaOH solution to
the flask and stir the mixture until the solid dissolves completely. Weigh approximately
0.8 g of sodium borohydride (NaBH4), record the mass in the laboratory notebook and
add the solid to the flask. The reaction should begin to effervesce releasing hydrogen gas
(H2) into the atmosphere. This is a good sign that the reduction is occurring. Let the
reaction continue stirring for five minutes.
Perform a TLC analysis of the reaction mixture to judge reaction completeness. For the
TLC analysis, include the starting material, a co-spot (both starting material and reaction
mixture on the same spot) and the crude product (reaction mixture). Develop the TLC
plate in a chamber using a 1:2 mixture of hexane/ethyl acetate. Visualize the spots on the
TLC plate using the I2/silica chamber (be careful not to breathe the I2 vapor or silica
dust). Make a sketch of the TLC plate in the laboratory notebook for future reference. An
example of the starting TLC plate is given below.
cp
cs
sm
Layout of TLC analysis
After the reaction is judged to be complete (starting material is no longer present in the
reaction mixture) dilute the reaction mixture with 5.0 mL of H2O. Quench the reaction by
slowly adding 3M HCl until the solution is neutral as judged by pH paper. Do not add too
much acid as the reaction will turn acidic. Stir the reaction mixture for 2-3 additional
minutes.
Pour the reaction mixture into a small separatory funnel. Rinse the round bottom flask
with a 5 mL portion of ethyl acetate (EtOAc) and add the solvent to the separatory funnel
along with an additional 15 mL portion of EtOAc. Extract the product from the aqueous
phase in the usual manner taking care to vent the separatory funnel to release pressure.
Allow the mixture in the separatory funnel to separate, drain the aqueous phase into a
flask and set aside. Pour the ethyl acetate solution from the separatory funnel into a 50
mL Erlenmeyer flask and add powdered sodium sulfate until the drying agent no longer
sticks together. Decant the ethyl acetate solution from the solid sodium sulfate into a
small Petri dish and allow the solvent to evaporate.
Data:
When the crystals of alcohol have dried completely obtain the mass of the
solid and record the data into the laboratory notebook. Obtain the melting point of both
vanillin and vanillyl alcohol and record the data into the laboratory notebook. Obtain an
FTIR spectrum of both the vanillin and the vanillyl alcohol.
Calculations: For this experiment calculate the limiting reagent as well as the theoretical
and % yields. Compare the melting points of the starting material and the product to the
literature value and comment on the purity. Report the data from the TLC analysis
including reaction progress and Rf of the starting material and the product.
Report:
% Yield
TLC data
vanillin mp
vanillyl alcohol mp
FTIR analysis of vanillin and vanillyl alcohol
comments on reaction success and product purity