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#1 2011-11-22 15:26:38

orgopete
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Conversion of cyclohexane-1,3-dione to glutaric acid

Yahoo!Answers in chemistry wrote:

When cyclohexan-1,3-dione is heated in the presence of Br2 (bromine) under basic conditions, the main organic products are 1,5-pentanedioc acid and CHBr3. Explain the result.

This is a combination question. The first reaction is a base catalyzed bromination. This reaction occurs three times. Its mechanism is illustrated for the first bromination step. It is repeated to give 2,2-dibromocyclohexane-1,3-dione.

At this point, the addition to a carbonyl group becomes evident. If hydroxide adds, it can reversibly eliminate hydroxide. However, as a alternate, it can eliminate the enolate of a dibromoketone (shown as its enolate). In the presence of bromine, a third bromination step can take place. A proton transfer step must also take place because the solution much contain excess hydroxide.

The product at this stage is a tribromomethyl ketone with a carboxylate ion. Addition and elimination of a tribromomethyl anion will give the disodium salt of pentanoic acid (glutaric acid). This step should be familiar to anyone familiar with the haloform reaction. [The tribromomethane will pick up a proton from water to give tribromomethane (bromoform).] Acidification will give the free glutaric acid.

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