Compund Y produced an orange precipitate when reacts with 2,4-DNP. Compound Y gives a pale yellow precipitate when reacts with I2/KOH. Compound Y does not react with AgNO3/NH3. what is compound Y?

1 Answer
Sep 27, 2016

Compound Y is a methyl ketone, #RC(=O)CH_3#


Ketones and aldehydes react with #"2,4-DNP"# to give brightly coloured phenylhydrazones. Aldehydes can be oxidized fairly easily by ammoniacal silver ion to give a carboxylic acid, and a silver mirror as the reduction product (see Tollens' test). Most ketones fail the Tollens test, so the unknown is likely a ketone. Methyl ketones give a positive result in the iodoform test, i.e. a precipitate of yellow #CHI_3#, as observed here. You will have to look up these reactions in your text.

As to the actual identity of the methyl ketone, you would take the melting point of the #"2,4-DNP"# derivative, and compare it with the copious literature (there are reams of literature detailing melting points of derivatives of carbonyl compounds just for this purpose of identification). You would have to make another derivative of the ketone, perhaps an ester of the resultant acid that was generated in the iodoform test, in order to identify the ketone unequivocally.