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Benzyl Alcohol and Benzoic Acid from Benzaldehyde and Strong Potash (Cannizzaro, Gattermann 1914)
Strong potash splits benzaldehyde in two: half is reduced to benzyl alcohol, half oxidised to benzoic acid (as potassium benzoate). 20 g of benzaldehyde gives about 8 g of benzyl alcohol, boiling at 206 °C; the benzoic acid is thrown down with hydrochloric acid.
Not given: the volumes of water and ether, the amount of hydrochloric acid and the benzoic acid yield.
Source: L. Gattermann, Practical Methods of Organic Chemistry (1914 ed.), Reaction 25, pp. 303-304. Picture: our drawing.
Intermediate
1 night plus a few hours
Instructions
1
1
Shake with strong potash
Shake with strong potash
Dissolve 18 g of potassium hydroxide in 12 g of water and let it cool. Put 20 g of benzaldehyde in a stoppered cylinder or other thick-walled vessel, add the cold potash and shake until a lasting emulsion forms.
Materials for this step:
Benzaldehyde1 20 g
Potassium Hydroxide1 18 g
Water1 12 gTools needed:
Weighing Scale
Measuring Cylinder
Corks2
2
Stand overnight
Stand overnight
Close the vessel with a cork, not a glass stopper (a glass stopper can stick fast), and let it stand overnight. A crystalline paste of potassium benzoate separates.
Tools needed:
Measuring CylinderCorks3
3
Extract with ether
Extract with ether
Add water until the paste dissolves to a clear solution. Shake it out several times with ether to take up the benzyl alcohol, keeping the watery alkaline layer for the benzoic acid.
Materials for this step:
Water1 amount not given
Diethyl Ether1 amount not givenTools needed:
Separatory Funnel
Glass Beaker4
4
Distil the benzyl alcohol
Distil the benzyl alcohol
Evaporate the ether and distil the residue. Benzyl alcohol passes over at 206 °C. Yield: about 8 g.
Tools needed:
Water Bath
Glass Distillation Flask
Water-Cooled Condenser
Thermometer
Bunsen Burner5
5
Precipitate the benzoic acid
Precipitate the benzoic acid
Acidify the alkaline solution with hydrochloric acid; benzoic acid is thrown down. Filter it off.
Materials for this step:
Hydrochloric Acid1 amount not givenTools needed:
Glass Beaker
Glass Funnel - Stemmed
Filter PaperMaterials
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- 1 18 gPlaceholder
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Tools Required
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