Organic Chemistry 2 - 09, Assig #6

Organic Chemistry 2 - 09, Assig #6 - THE FOLLOWING IS A...

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THE FOLLOWING IS A SHORT DISCUSSION OF THE CONCEPT OF PROTECTING GROUPS. This topic was discussed at the end of one lecture and repeated at the beginning of the next one. This short discussion is designed to further illustrate this important synthesis strategy. Question 10 and parts of 11, 12 and 13 test your understanding of the reactions involved in this approach. CHM 2120 Concept Protecting groups. The purpose: to hide temporarily a relatively reactive functional group so that chemical changes can be made elsewhere in the molecule. Once the desired changes have been accomplished the protecting group is removed and the original functional group is regenerated. This processes used commonly in complex syntheses and many different protecting groups are available fort he various common functional groups such as ketones, aldehydes, amines, alcohols, etc. The reason several different protecting groups are needed for a single functional group is that a single protecting group is not likely to be useful under all reaction conditions. In this course only one protecting group for ketones and aldehydes, and two protecting groups for alcohols will be illustrated. A. The ketal [acetal] protecting group for ketones and aldehydes. Reaction of carbonyl compounds, ketones and aldehydes, but not esters or amides or acids, with alcohols in the presence of sulfuric acid leads to formation of ketal [acetals] and water. This is an equilibrium reaction and the equilibrium can be driven to completion by removal of water from the reaction medium by either a chemical or physical process. Conversely, a ketal [acetal] can be converted essentially completely into its parent ketone [aldehyde] by exposing it to sulfuric acid in the presence of excess water. The overall process is illustrated for butanone
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Organic Chemistry 2 - 09, Assig #6 - THE FOLLOWING IS A...

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