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    Posted by : Arun SS
Arun SS
 Q.
Give chemical tests to distinguish between the following pairs of compounds:

(i) Ethanal and Propanal

(ii) Phenol and Benzoic acid

(b) How will you bring about the following conversions?

(i) Benzoic acid to benzaldehyde

(ii) Ethanal to but-2-enal

(iii) Propanone to propene

Give complete reaction in each case.

Ans.
Posted by : Arun SS   Posted on 29 Dec 2010, 11:07 PM    
 (a) (i) Ethanal and propanal can be distinguished by iodoform test.
Iodoform test: Aldehydes and ketones having at least one methyl group linked to the carbonyl carbon atom responds to the iodoform test. Ethanal having one methyl group linked to the carbonyl carbon atom responds to this test. But propanal does not have a methyl group linked to the carbonyl carbon atom; thus, it does not respond to this state.   
(ii) Phenol and benzoic acid can be distinguished by ferric chloride test.
Ferric chloride test: Phenol reacts with neutral FeCl3 to form ferric phenoxide complex giving violet colouration.
 
But benzoic acid reacts with neutral FeCl3 to give a buff coloured precipitate of ferric benzoate.

(b)(i)