Páginas: 5 (1053 palabras) Publicado: 19 de agosto de 2010
The Cannizzaro Reaction

Mayo, Pike, Trumper, Strange de Soria. Microscale Organic Laboratory. New York: John
Wiley and Sons, 2002.

Strange de Soria, Luise. “Student Survival Guide”. 2004.

The purpose of this experiment is to oxidize and reduce an aromaticaldehyde to form benzoic acid and benzyl alcohol. We will also separate the layers into two products, a carboxylic acid and a neutral alcohol.

Summary of the Theory behind the Cannizzaro Reaction:
The Cannizzaro reaction consists of an oxidation-reduction reaction between a hydroxide ion and aldehydes without α-hydrogen atoms. With the presence of a strong base, the first aldehyde molecule reducesto a second aldehyde molecule and then becomes a primary alcohol. Within this process the molecule oxidizes itself to the corresponding carboxylate anion. If the aldehyde does possess an α-hydrogen atom, the α-carbon will deprotonate when there is a base present and the reaction will not go through this kind of reaction (an Aldol reaction will usually occur with the resulting enolate).
Themechanism of this reaction happens as follows…

Reaction Analysis:
Balanced Chemical Equation:
* (ClC7H5O)2 + KOH + H+ → ClC7H4OH + ClC7H4O2H
Theoretical yield:
Alcohol Layer
1) Take the amount of 4-chlorobenzaldehyde and divide it by its molecular weight
* 0.3g ÷ 140.57g/mol = 0.002mol
2) Take the value found in step 1 and multiply it by the molecular weight of theproduct
* 0.002mol x 144.52g/mol = 0.289g theoretical yield
Acid Layer
1) Take the value found in step 1 of alcohol layer and multiply it by the molecular weight of the product
* 0.002mol x 142.25g/mol = 0.285g theoretical yield
Potential side products:
* Leftover starting material

Add 150mg of 4-chlorobenzaldehyde and 0.4mL of methanol to a 5mL conical vial on areflux condenser with a spin vane. Gently stir while adding 0.4mL of 11M KOH. Run the water through the condenser and heat while stirring between 65oC – 75oC for one hour. Cool to room temperature and add 2mL of cold deionized water to the solution in a seperatory funnel. Extract the solution with 3 portions of 0.5mL of methylene chloride. You should see the layers begin to form. Thecarboxylic acid is in the water layer and the alcohol is in the methylene chloride layer. Both layers should be stored until the following week.
To recover the p-chlorobenzyl alcohol, take the methylene chloride layer and wash it with two portions of 0.25mL of 10% sodium carbonate and 0.5mL of water (this will neutralize the solution of residual acid). Once the layer has been extracted, dry it withabout 150mg of granular anhydrous sodium sulfate. Allow the product to dry and collect product weight and melting point.
To recover the p-chlorobenzoic acid add 2mL of deionized water and approximately 0.4mL of concentrated HCl until the solution is acidic. Filtrate with a Hirsh funnel and collect the white precipitate, allow the product to dry and gather its melting point and weight.Observations:
We increased the reaction by a factor of 2. After the ingredients were added to recover the acid and the alcohol layer we realized that the layers were mixed up. 1.5mL of HCl was added to the alcohol layer so to make the solution neutral, 9mL of deionized water and 7mL of 10% sodium carbonate were added. We used litmus strips to check the acidity of the solution to make sure it wasneutralized. The acid layer had 1mL of deionized water and 1mL of 10% sodium carbonate added so we simply added 1.5mL of HCl before the product was filtrated out of the solution. The product of the alcohol layer was a purplish color when extracted yielding purplish crystals the following week when weight and melting point were measured.

Product Data for Alcohol Layer |
Product |...
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