Borohydride Reduction of Vanillin to Vanillyl Alcohol

Borohydride Reduction of Vanillin to Vanillyl Alcohol

Operational Organic Chemistry a Problem Solving Approach to the Laboratory Course, 4th edition, by John Lehman, Experiment 29, pgs. 246 – 254.

Introduction

The purpose of this experiment is to see if vanillin can be synthesized to vanillyl alcohol through reduction with sodium borohydide.

Balanced Equations

Calculations of Quantities of Reactants Required

List of Material and Supplies Needed

Chemicals:

Vanillin

Sodium Borohydride

Vanillyl Alcohol

MM

152.2

37.83

154.2

mol

amount

Bp

285

400d

d

density

Experimental Procedure

Use a 125 mL Erlenmeyer flask to dissolve 25.0 mmol of Vanillin (FW 152.15 g/mol) in 30 mL 1M NaBH4.

If the mixture does not dissolve after 5 minutes of continuous stirring add another 5 mL NaBH4 and cool the solution to just below 15°C.

In a small beaker dissolve 12.0 mmol of NaBH4 (FW 37.83 g/mol) in about 6 mL of 1 M NaBH4.

Remove the vanillin solution from the ice bath, and add the NaBH4 solution in small portions to the vanillin over a 5 minute period. Make sure the temperature of the vanillin solution does not rise above 25 °C. Once all the NaBH4 has been added, let the solution sit at room temperature for 30 minutes with frequent swirling.

Place the reaction mixture in an ice bath and carefully acidify the solution with 6 M hydrochloric acid. Perform this step carefully, as the solution will foam and foam will contain vanillyl alcohol.

Check the pH with litmus paper to ensure it is acidic. Cool the mixture in the ice bath for an additional 10 minutes.

Collect the vanillyl alcohol by vacuum filtration and wash the crystals with cold water. Store the product in a container for a week and once the sample has dried determine its mass and melting point.

Data and Results

Mass of product with filter paper and weigh boat = 2.420g

Mass of filter paper and weigh boat alone = 2.200g

Mass of vanillyl alcohol obtained = 0.220g

Melting point = start temperature of 97°C and complete melting at 99°C

Discussion and Conclusion

The experiment attempted to reduce vanillin to vanillyl alcohol using a reduction reaction with sodium borohydride. The reduction reaction was completed in a base medium with NaOH because an acidic medium such as H3O+