Sodium Borohydride Reduction of Vanillin: A Low Solvent Synthesis of Vanillyl Alcohol. A Lab by Carl S. Lecher, Marian College, Indianapolis, IN. (clecher@marian.edu)

Performed by Marcus Nappo (mef68@unh.edu) & Kevin Heiser (kpb7@unh.edu)

University of New Hampshire at Manchester




vanillin.jpg
(No permission needed: Public Domain)



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Organic Chemistry: A Green Approach




There are 12 Green Chemistry Principles possibilities used during this procedure. Green chemistry principles are educated steps helping to reduce chemical hazards, negative environmental impact, and limits waste production. (1)

  1. Analyze in Real-Time to Prevent Pollution
  2. Avoid Chemical Derivatives
  3. Design for Degradation
  4. Design Less Hazardous Chemical Syntheses
  5. Design Safer Chemicals and Products
  6. Increase Energy Efficiency
  7. Maximize Atom Economy
  8. Minimize the Potential for Accidents
  9. Prevent Waste
  10. Use Catalysts
  11. Use Renewable Feed stocks
  12. Use Safer Solvents/Reaction Conditions

Listed below are these principles used during this experiment:


  • Use of renewable feed stock: Principle # 11- Vanillin, natural aromatic compound native to Mexico. Used in flavoring beverages, cooking, and medical treatments.
  • Benign solvent and reactants: Principle # 12- Ethanol is used as the solvent which stability as no acid functional group is present. NaBH4 is used in place of LiAlH4 because of violence with water, alcohols, and phenols.
  • Reducing the solvent use: Principle # 9 – An excess amount of NaBH4 is used to compensate for the little amount of ethanol used during the experiment. We used only enough to dissolve the reactant.
  • Benign product: Principle # 5 – The identification of vanillyl alcohol crystals.



The Project
Attempted Plans:

  • PLAN A: Work with a local high school teacher to develop an experiment to extract essential oils from organic substances.

-This plan did not work out due to communication problems with the teacher. We were unable to develop an experiment which met both of our needs. From here we moved to our Plan B.

  • PLAN B: Find an existing reduction/oxidation lab protocol in which benign solvents are used instead of ones that are bad for the environment. Instead of visiting the school, a videotaping of the experiment would be performed.

  • PLAN C: If both plans A and B failed, no experiment would be performed and green chemistry, as a whole, would be the focus of our project.

  • Ultimately, we decided on PLAN B.




A Traditional RedOx Reaction



poison-sign.jpg (No permission needed: Public Domain)


Traditionally, and most commonly, a reduction oxidation reaction is carried out by potassium permanganate, sulfuric acid, and phosphoric acid. Though these chemical agents have proven to be quite effective in their ability to oxidize and reduce iron, they are not safe or “green.”
One main hazard lies in phosphoric acid and its caustic properties. These include being able to burn, corrode, or destroy living tissue. The MSDS sheet for phosphoric acid states that it is extremely corrosive to the lungs and skin. With prolonged use, chronic effects can arise in the blood, liver, skin, eyes, and bone marrow as well. Potassium Permanganate poses mutagenic effects in bacteria and yeasts. This usually means there’s a 90% chance of it being carcinogenic to humans. Its MSDS sheet also states that it could also cause negative, chronic reproductive effects in animals. Lastly, sulfuric acid’s MSDS sheet states many problematic properties. For one, it is instable in numerous conditions including excessive heat, organic materials, and exposure to water, oxidizers, amines, and bases. In addition, it is classified and proven to cause cancer in humans.











Our Green Experiment: Sodium Borohydride Reduction of Vanillin


Vanilla, the fresh smell every one loves or the best type of ice cream to go with apple pie, is an aromatic chemical compound known as vanillin
(CH3O)(OH)C6H3CHO. This natural organic compound found in Mexico is derived from the pods of a vanilla plant. Although it is considered to be a highly valuable substance, it is very expensive to produce. To provide an economical alternative, synthetic vanillin is produced at a cheaper rate. Vanillin is synthesized from lignin which is a complex polymer that gives rigidity to trees. After cellulose, lignin is the most abundant organic matter on Earth. Less than 1% of the compounds in whole sale products are natural vanillin. (2)

Synthetic vanillin is used widely in everyday products. Coca-Cola, a well known soda beverage company is one of the world’s largest customers of synthetic vanillin. The vanillin is used as a flavor additive for the beverages produced. Other products that use vanillin are candles, incenses, and perfumes. (2)



OUR GOAL
: Vanillyl Alcohol which is made by the REDUCTION of vanillin is done with “green goggles”. We want to look a look at two crucial points;
1) Elimination of hazardous reaction and products- (see green principles)
· Apply to principle # 12
· Apply to principle # 5


2) Environmental impact while maximizing safety-(see green principles)
· Apply to principle # 11
· Apply to principle # 9







Materials:

4-hydroxy-3-methoxybenzaldehyde, a.k.a. Vanillin
NaBH4 (Sodium Borohydride) [3.42 M in 1.0 M NaOH]
HCl (Hydrochloric acid)
Ethanol
Drop wise funnel
Round bottom flask
100ml flask
Thermometer
pH strips
Vacuum filtration apparatus
Stir bar
Ice Bath
Ring Stand
Multiple clamps


Safety Plan:


All standard laboratory safety procedures were implemented during this experiment, including:
  • Wearing gloves
  • Wearing goggles
  • Wearing lab coats
  • Working in the fume hood
  • Practicing extreme, overall caution

In this reaction there are some risks associated with the chemicals -- mainly the sodium borohydride. These risks can be overcome with careful attention to the experimental procedure. After looking at the MSDS sheet for sodium borohydride, we noticed that it may react with water to release flammable gases. According to the lab, this can be overcome by adding the NaBH4 slowly to the solvent mixture of vanillin and ethanol. Another chemical associated with risk is the 6m HCL (Hydrochloric Acid) used. Hydrogen gas is formed as well as causing the solution to become acidic. MSDS link is located below for all chemicals used during the experiment.


Procedure:


Synthesis of Vanillyl Alcohol:


1. Weigh 2.5 - 2.6g of vanillin into a 50ml beaker.

- Record weight
- Calculate mmol


2. Transfer Vanillin to a 25ml round bottom flask using a solid addition funnel.
- Rinse excess into with 5.0ml of ethanol (This will be used as the solvent in the experiment.)


3. Add stir bar to round bottom flask and dissolve the vanillin into the ethanol. (If unsuccessful with stir bar alone, you can gently warm the flask with the palm of your hand.)

4. Add 5.0ml of sodium borohydride (NaBH4) solution to the dropping funnel.
- Clamp round bottom flask to ring stand and lower into an ice bath.

- Slowly, drop by drop, add the NaBH
4 to the vanillin and ethanol. (Make sure the temperature is monitored and doesn’t rise above 25 degrees Celsius.)
- Process should take about 10 minutes to complete.


5. When addition of NaBH4 is complete, remove from ice bath and stir at room temperature for 5 minutes.

6. Return to ice bath apparatus.

- Add 6M HCl drop wise, stirring until all H2 gases have completely evolved.
- Check pH to make sure the solution is now acidic.

7. Cool and stir in the ice bath once again for 10 minutes until a precipitate forms.


Separation:


8. Collect the solid precipitate by vacuum filtration. (Small amount of distilled water can be used to rinse the flask out onto the filter paper.)
- Allow solid to dry for at least 2 minutes under vacuum.


9. Air-dry for 24 hours. (Do not oven dry!)
- The unusable filtrate can be washed down the sink.


10. Obtain your end product of Vanillyl alcohol.

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Calculations:

Though theoretical yield, melting point, and end product identity can be obtained, we did not perform these calculations. Please refer to the lab protocol link below for more information on these last parts of the lab.

Full Protocol


















References:

1 - 12 principles web site
2 - Vanillin Coke