Fehlingreaktioner

Fehlingreaktioner are qualitative tests used to detect the presence of reducing sugars and aldehydes. Developed by Hermann von Fehling in 1849, these reactions rely on the reducing properties of these compounds. The Fehling's solution is typically prepared as two separate solutions, Fehling's solution A (an aqueous solution of copper(II) sulfate) and Fehling's solution B (an alkaline solution of potassium sodium tartrate). When these two solutions are mixed, they form a complex of copper(II) ions in an alkaline environment.

When a sample containing a reducing sugar or aldehyde is added to the Fehling's solution and heated, the copper(II) ions (Cu2+) are reduced to copper(I) ions (Cu+). This reduction is accompanied by the formation of a brick-red precipitate of copper(I) oxide (Cu2O). The intensity of the red precipitate is proportional to the amount of reducing sugar or aldehyde present. Aldehydes are readily oxidized to carboxylic acids by Fehling's solution. Ketones, with the exception of alpha-hydroxy ketones, do not react with Fehling's solution. This differentiating capability makes the Fehling's reaction a useful tool in organic chemistry for identifying the presence of specific functional groups. The reaction is typically carried out in a water bath to ensure controlled heating.