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Q & A: Baeyer’s Test

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Most recent answer: 12/22/2010
Q:
How does the Baeyer's test for unsaturation works?
- Danica Fernandez
Wesleyan University-Philippines
A:
  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
| | | |
H-C=C-H + KMnO4 ------> H- C - C-H + Mn02
| |
H H

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.

Jason

(published on 10/22/2007)

Follow-Up #1: What is the chemical equation of benzene?

Q:
what is the chemical equation of benzene?
- tootchie lopez (age 18)
davao city,philippines
A:
A benzene molecule, C6H6, consists of six carbon atoms and six hydrogen atoms.   The carbon atoms are bound together to form a hexagonal ring.  Each carbon atom has an additional hydrogen atom attached to it. 

LeeH

(published on 08/13/2009)

Follow-Up #2: What is the chemical notation for benzene?

Q:
what is the chemical equation of benzene?
- Anonymous (age 16)
zamboanga, philippines
A:
Benzene is a molecule that contains six carbon atoms and six hydrogen atoms in a ring structure.   The chemical notation is C6H6.  There is a nice Wikipedia article on it: 

LeeH

(published on 12/22/2010)

Follow-up on this answer.