|First off, thanks for asking an organic chemistry question. I just love organic!
The Baeyer test for unsaturation is for determining the presence of carbon-carbon double bonded compounds, called alkenes or carbon-carbon trible bonded compounds, called alkyne bonds.
The Baeyer test uses dilute Pottasium Permanganate to Oxidize the carbon-carbon double or triple bond. It's called oxidation because the double bond is replaced by a hydroxy group (an OH group). The carbon's charge goes from being +1 to +2, so it loses an electron (and is thus oxidized)
The reaction looks like this:
H H OH OH
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H-C=C-H + KMnO4 ------> H- C - C-H + Mn02
An alkene is replaced with a diol (a compound with 2 hydroxy groups). Evidence for the reaction is there because the purple Pottasium permanganate goes colorless.
Alkynes work the same way, but a 4 hydroxy quattrol is produced (with 2 hydroxy groups on each carbon).
The reaction is important because it doesn't work on alkanes (compounds with carbon-carbon single bonds) or aromatic compounds.
However, the test has a few drawbacks. Aldehydes (terminal carbonyls ... carbon double bonded to Oxygen) will also be oxidized (to carboxylic acids) and formic acid (ethanoic acid) and its esters are known to give positive tests.
I hope that explains it sufficiently.
(republished on 07/13/06)
(published on 08/29/09)
(published on 12/23/10)