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Benzyl Alcohol and Benzoic Acid from Benzaldehyde and Strong Potash (Cannizzaro, Gattermann 1914)
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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.
Ophakathi
1 night plus a few hours

Imiyalelo

1

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.

Izinto zokwakha zalesi sinyathelo:

I-BenzaldehydeI-Benzaldehyde1 20 g
I-potassium hydroxideI-potassium hydroxide1 18 g
AmanziAmanzi1 12 g

Amathuluzi adingekayo:

IsikaliIsikali
Isilinda sokukalaIsilinda sokukala
Ama-corkAma-cork
2

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.

Amathuluzi adingekayo:

Isilinda sokukalaIsilinda sokukala
Ama-corkAma-cork
3

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.

Izinto zokwakha zalesi sinyathelo:

AmanziAmanzi1 amount not given
I-diethyl etherI-diethyl ether1 amount not given

Amathuluzi adingekayo:

Ifasitela lokwehlukanisaIfasitela lokwehlukanisa
Ibhikha LengilaziIbhikha Lengilazi
4

Distil the benzyl alcohol

Evaporate the ether and distil the residue. Benzyl alcohol passes over at 206 °C. Yield: about 8 g.

Amathuluzi adingekayo:

Ibhavu LamanziIbhavu Lamanzi
Ifulakhi Lengilazi LokuhluzaIfulakhi Lengilazi Lokuhluza
Isijiyisi esipholiswa ngamanziIsijiyisi esipholiswa ngamanzi
IthemomithaIthemomitha
Isibani se-BunsenIsibani se-Bunsen
5

Precipitate the benzoic acid

Acidify the alkaline solution with hydrochloric acid; benzoic acid is thrown down. Filter it off.

Izinto zokwakha zalesi sinyathelo:

I-hydrochloric acidI-hydrochloric acid1 amount not given

Amathuluzi adingekayo:

Ibhikha LengilaziIbhikha Lengilazi
Ifanela Lengilazi ElinomlomoIfanela Lengilazi Elinomlomo
Iphepha LokuhluzaIphepha Lokuhluza

Izinto

5

Amathuluzi Adingekayo

12

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I-benzoic acid

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I-Benzyl Alcohol

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