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 a neutral 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.