Baeyer's reagent

Baeyer's reagent, named after the German organic chemist Adolf von Baeyer, is used in organic chemistry as a qualitative test for the presence of unsaturation, such as double bonds. The bromine test is also able to determine the presence of unsaturation.

Baeyer's reagent is an alkaline solution of potassium permanganate, which is a powerful oxidant. Reaction with double or triple bonds (-C=C- or -C≡C-) in an organic material causes the color to fade from purplish-pink to brown. It is a syn addition reaction. Aldehydes and formic acid (and formic acid esters) also give a positive test.

The brown solid manganese(IV) oxide precipitates out of solution when potassium permanganate reacts with a double or triple bond.