Aldehydes, Ketones and Carboxylic Acids

Aldehydes, Ketones and Carboxylic Acids

Question

(a) Illustrate the following name reactions:

(i) Cannizzaro’s reaction

(ii) Clemmensen reduction

(b) How would you obtain the following?

(i) But-2-enal from ethanal

(ii) Butanoic acid from butanol

(iii) Benzoic acid from ethylbenzene

 OR

 (a) Given chemical tests to distinguish between the following:

(i) Benzoic acid and ethyl benzoate

(ii) Benzaldehyde and acetophenone


(b) Complete each synthesis by giving missing reagents or products in the following:

Answer

(i) Cannizaro reaction

In this reaction, the aldehydes which do not have a a-hydrogen atom, undergo self -oxidation and reduction (disproportionation) reaction on treatment with a concentrated alkali.

Example:

(ii) Clemmensen reduction

In this reaction, the carbonyl compounds are reduced in presence of zinc amalgam to give the corresponding alkane.

 

(b)

(i) But-2-enal from ethanal

 

(ii) Butanoic acid from butanol

 stack CH subscript 3 minus CH subscript 2 minus CH subscript 2 minus OH with Butan minus 1 minus ol below space rightwards arrow with CrO subscript 3 minus straight H subscript 2 SO subscript 4 on top space stack CH subscript 3 CH subscript 2 CH subscript 2 COOH with Butaonic space acid below

 

(iii) Benzoic acid from ethylbenzene

 
Or

(a)

(i) Benzoic acid and Ethyl benzoate can be distinguished by sodium bicarbonate test.

Sodium bicarbonate test:

Acids react with NaHCO3 to produce brisk effervescence due to the evolution of CO2gas.Benzoic acid being an acid responds to this test, but ethyl benzoate does not.

 stack straight C subscript 6 straight H subscript 5 COOH with Banzoic space acid below space plus NaHCO subscript 3 space rightwards arrow stack straight C subscript 6 straight H subscript 5 COONa with sodium space benzoate below space plus CO subscript 2 space upwards arrow space plus straight H subscript 2 straight O
straight C subscript 6 straight H subscript 5 COOC subscript 2 straight H subscript 5 space plus NaHCO subscript 3 space rightwards arrow No space effervescence space due space to space evolution space of space CO subscript 2 space gas

(ii) Benzaldehyde (C6H5CHO) and acetophenone (C6H5COCH3) can be distinguished by iodoform test.

Acetophenone, being a methyl ketone on treatment with I2/NaOH undergoes iodoform reaction to give a yellow ppt. of iodoform. On the other hand, benzaldehyde does not give this test.

b)

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