Oxidation to carboxylic acids [Tollens]

Oxidation to carboxylic acids [Tollens] Definition:


When Ag2O is added to aldehydes, carboxylic acids are formed. The results in the formation of silver metal (“silver mirror”) a reaction known as the Tollens test.



Oxidation to carboxylic acids [Tollens] Explained:


In Tollens’ reaction, a solution of silver ion precipitates a silver mirror on exposure to an aldehyde. Because ketones have no hydrogen on the carbonyl carbon, they do not undergo this oxidation reaction. The Tollens’ test is used for detects the presence of readily oxidized functional groups in organic molecules and employed to produce shiny silver mirrors on a glass surface. Tollens’ test is not commonly used in large-scale syntheses of carboxylic acid.

Tollens reagent consists of a solution of silver nitrate and ammonia.  Aqueous silver nitrate is mixed with aqueous sodium hydroxide:

AgNO3+ NaOH → AgOH + HNO3

2 AgOH → Ag2O + H2O

Then aqueous ammonia is added:

Ag2O + 4 NH3 + H2O → 2 Ag(NH3)²+ + 2 OH‾

Tollens reagent oxidizes an aldehyde into the corresponding carboxylic acid: