ORGLIST:Lieberman-Burchard Reaction

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From: antonio regla (areglac$##$
Date: Sun Nov 10 2002 - 14:19:03 EST

Dear List members:

Cholesterol reacts with acetic anhydride and concentrated sulfuric acid, to give a positive test, which is a blue coloration. Recently, a graduate student at my university asked me what reactions are involved in this test. We looked up on books, on the net, and very little regarding the reactions involved was found. There were a lot of references on the clinical side of the topic. We sat down and wrote down reactions, one of them was the esterification of the OH on cholesterol, however it seems very unlikely that this ester absorbs at such high wavelenghts, around 620 nm. Also, I wonder if acetic anhydride can acetylate alcohols in strongly acidic media such as concentrated sulfuric acid. I wonder if dehydration is taking place, followed by a 1,2-hydride shift, giving an allylic cation which would give rise to the colored species being formed. Does anyone have any ideas on this subject, we will appreciate any information you may provide.


Antonio Regla

Facultad de Farmacia

Universidad Autonoma de Morelos

Cuernavaca, Mexico

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