Question

29. The product obtained by Cannizzaro's reaction is -
(a) Acid
(b) Ester and alcohol
(c) Alcohol
(d) Acid and alcohol​

Answer 1

Answer:

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Explanation:

Answer

(a) Aldol condensation

It is a reaction between two molecules of carbonyl compounds having alpha hydrogen atoms to form beta hydroxy aldehyde (aldol) or beta hydroxy ketone (ketone). It occurs in presence of dilute base NaOH, KOH or Na

2

CO

3

. Thus, ethanal and propanal will give following products.

2CH

3

−CHO

dilNaOH

CH

3

−CHOH−CH

2

−CHO

(i)H

+

(ii)Δ

CH

3

−CH=CH−CHO

(b) Cannizzaro reaction

Aldehydes (not having alpha H atom) undergo self oxidation and reduction (disproportionation) in presence of concentrated aqueous or alcoholic alkali. The products are a mixture of alcohol and salt of carboxylic acid. One aldehyde molecule is reduced to alcohol and other aldehyde molecule is oxidized to salt of carboxylic acid.

Thus when formaldehdye is treated with aq NaOH, a mixture of methyl alcohol and sodium formate is obtained.

2HCHO+NaOH→CH

3

−OH+HCOONa

(c) Esterification

A carboxylic acid (or acid chloride or acid anhydride) reacts with an alcohol in presence of an acid cataylst.

C

2

H

5

−OH+CH

3

COOH

H

+

CH

3

−COO−C

2

H

5

+H

2

O

C

2

H

5

−OH+(CH

3

CO)

2

O

H

+

CH

3

−COO−C

2

H

5

+CH

3

COOH

C

2

H

5

−OH+CH

3

COCl

pyridine

CH

3

−COO−C

2

H

5

+HCl

(d) Decarboxylation

When anhydrous sodium salt of carboxylic acid is fused with soda lime (sodium hydroxide and calcium oxide in the ratio 3:1) itgives hydrocarbon containing one carbon atom less than the carboxylic acid. The net result is loss of a molecule of carbon dioxide from carboxylic acid.

CH

3

COONa+NaOH

CaO

Δ

CH

4

+Na

2

CO

3

Answer 2

Answer:

The product obtained in the Cannizzaro reaction are alcohol and acid.

Therefore, the option (d) is correct.

Explanation:

• Cannizzaro reaction is given by those aldehydes which do not have any alpha-hydrogen such as formaldehyde (HCHO), benzaldehyde C₆H₅CHO etc.
• Cannizzaro reaction is the self oxidation or reduction or disproportionation reaction which is undergone by aldehydes with no $\alpha$- hydrogens.
• It consists in treating aldehyde with alcoholic or concentrated aqueous solution pf sodium or potassium hydroxide. After the reaction, alcohol and salt of carboxylic acid are produced.

  E.g.(1):   2HCHO   +   NaOH (conc.)   $\longrightarrow$   CH₃OH    +   HCOONa

          Formaldehyde                                    Methanol       Sod. formate

 E.g.(2):  C₆H₅CHO   +    NaOH     $\longrightarrow$   C₆H₅CH₂OH   +   C₆H₅COONa

           Benzaldehyde     (conc.)             Benzyl alcohol      Sod. benzoate