Borohydride Reduction of Vanillin to Vanillyl Alcohol
Experiment 29 – Borohydride Reduction of Vanillin to Vanillyl Alcohol
Goal
To perform a sodium borohydride reduction of an aldehyde to produce an alcohol.
Reading and Working Ahead
Your discussion should include a mechanism for this reaction.
Review:
OP 12 – Vacuum filtration
OP 28 – Melting point (using Mel-Temp®)
Procedure Notes
Calculate the necessary mass of vanillin and sodium borohydride for the procedure below. Also calculate theoretical yield of vanillyl alcohol.
You will not design you own procedure, instead, use the procedure below.
Dissolve 25.0 mmol of vanillin in 30 mL 1 M sodium hydroxide in a 125 mL Erlenmeyer flask. If the mixture does not dissolve after 5 minutes of continuous stirring, add another 5 mL sodium hydroxide. Cool the solution to just below 15 oC. In a small beaker, dissolve 12.0 mmol of sodium borohydride in about 6 mL of 1 M sodium hydroxide. Remove the vanillin solution from the ice bath, and add the sodium borohydride solution in small portions to the vanillin over a 5 minute period. Make sure the temperature of the vanillin solution stays in the range of 20-25 oC. (In fact, this is the ideal temperature range for the rest of the lab, through acidification and initial crystal formation.) Once all of the sodium borohydride has been added, let the solution sit at room temperature for 30 minutes, with frequent swirling. Acidify the solution with 6 M hydrochloric acid (6-10 mL may be required), keeping the temperature between 20 and 25 oC. Perform this step carefully, as the solution will foam and the foam will contain vanillyl alcohol. Also, if the mixture gets too hot at this stage, the product will not crystallize properly. Check the pH with litmus paper to ensure it is acidic. Once crystal formation has begun, cool the mixture in the ice bath for 15 minutes. Collect the vanillyl alcohol by vacuum filtration, and wash the crystals with cold water. Store the product in a container specified by the instructor
Goal
To perform a sodium borohydride reduction of an aldehyde to produce an alcohol.
Reading and Working Ahead
Your discussion should include a mechanism for this reaction.
Review:
OP 12 – Vacuum filtration
OP 28 – Melting point (using Mel-Temp®)
Procedure Notes
Calculate the necessary mass of vanillin and sodium borohydride for the procedure below. Also calculate theoretical yield of vanillyl alcohol.
You will not design you own procedure, instead, use the procedure below.
Dissolve 25.0 mmol of vanillin in 30 mL 1 M sodium hydroxide in a 125 mL Erlenmeyer flask. If the mixture does not dissolve after 5 minutes of continuous stirring, add another 5 mL sodium hydroxide. Cool the solution to just below 15 oC. In a small beaker, dissolve 12.0 mmol of sodium borohydride in about 6 mL of 1 M sodium hydroxide. Remove the vanillin solution from the ice bath, and add the sodium borohydride solution in small portions to the vanillin over a 5 minute period. Make sure the temperature of the vanillin solution stays in the range of 20-25 oC. (In fact, this is the ideal temperature range for the rest of the lab, through acidification and initial crystal formation.) Once all of the sodium borohydride has been added, let the solution sit at room temperature for 30 minutes, with frequent swirling. Acidify the solution with 6 M hydrochloric acid (6-10 mL may be required), keeping the temperature between 20 and 25 oC. Perform this step carefully, as the solution will foam and the foam will contain vanillyl alcohol. Also, if the mixture gets too hot at this stage, the product will not crystallize properly. Check the pH with litmus paper to ensure it is acidic. Once crystal formation has begun, cool the mixture in the ice bath for 15 minutes. Collect the vanillyl alcohol by vacuum filtration, and wash the crystals with cold water. Store the product in a container specified by the instructor