Posted by: Mark Foreman | January 21, 2012

Organic oxidation and reduction

One of the first things we need to deal with is the carbonyl group, a vast series of compounds contain this functional group. In common with much of organic chemistry the same functional groups, reactions and ideas come back time and time again. I hold the view that a first year at Chalmers needs to know only about eight organic reactions in total. I might be wrong with the exact count so I might change the number on the list.

If we need to reduce (unoxidise) a carbonyl group then the classic method these days is to use a maingroup hydride such as “lithium aluminium hydride”. You will need to know how to select the right reduction reagent, here are some tips for understanding why lithium aluminium hydride is so much stronger as a reducing agent than sodium borohydride. In general for inorganic chemists boron hydrides are interesting molecules as you can get lots of interesting shaped molecules, these include things like “interesting bonds” such as three centred two electron bonds like the banana bonds in diborane but in most first year classes you do not need to go in detail into this topic.

Back to the first year chemistry.

The reduction of an ester forms an alcohol. What happens when borohydride is used is that a nucleophilic attack by a hydrogen occurs on the carbonyl carbon. This is promoted by the coordination of the carbonyl oxygen to the cation which is associated with the borohydride. I will write some more shortly.

To do the oxidation which goes the other way, then it is typical to use a chromium(VI) reagent. The bench monkey has an interesting view of the matter.

The next reaction is ester formation

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Responses

  1. this is my comments ! thx for all !


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