Qualitative Tests for Carbonyls: Aldehydes vs. Ketones. Various chemical tests identifying ketones and aldehydes are used in this experiment in order to identify an unknown carbonyl compound.

Laboratory 6

Qualitative Tests for Carbonyls: Aldehydes vs. Ketones

Introduction

Various chemical seeks identifying ketones and aldehydes atomic number 18 utilize in this experiment in order to identify an unknow carbonyl compound. The tests used are: 2,4-dinitrophenylhydrazone test, Tollens Test, Benedicts Test, Chromic panelling Test, aka Bordwell-Wellman Test, Schiffs Test, and Iodoform Test. These classification tests provide results based on color change or formation of precipitation, which is then used to determine the identity of the functional group.

The firstborn test, the 2,4-dinitrophenylhydrazone test, determines the presence of a carbon-oxygen double bond. Bradys reagent, another name for the test, is a solution of 2,4-dinitrophenylhydrazine, methanol, and sulfuric acid. When performing the test, a bright orange or yellow precipitate shows the presence of an aldehyde or ketone. This test proceeds via a nucleophilic addition-elimination response, as shown below.¹

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The Tollens test is used to sleep with between aldehydes and ketones. The reaction works due to the fact that contradictory ketones, aldehydes can be readily oxidized. The Tollens test is also known as the silver- reverberate test, because when the test is positive for aldehydes, a silver mirror forms on the side of the test tube. A sample reaction is shown below.

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The Benedicts Test and Chromic Acid Test both work in similar mould as the Tollens Test. In the Benedicts Test, cupric salts are used as the oxidizing reagent rather than the silver nitrate. An aldehyde is identified by a brick-red precipitate, composition ketones have no reaction.

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The Chromic Acid Tests, sometimes known as the Bordwell-Wellman Test, uses chromic acid to oxidize the aldehydes to carboxylic acids. Ketones do not react. When oxidized, the...

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