20. Some alcohols undergo rearrangement or other unwanted side reactions when they dehydrate in acid. Alcohols may be dehydrated under mildly basic conditions using phosphorus oxychloride (POCI3) in pyridine. The alcohol reacts with phosphorus oxychloride much like it reacts with tosyl chloride, displacing a chloride ion from phosphorus to give an alkyl dichlorophosphate ester. The dichlorophosphate group is an outstanding leaving group. Pyridine reacts as a base with the dichlorophosphate ester to give an E2 elimination. Propose a reasonable mechanism for the dehydration of 2- methylcyclohexanol by POCl3 in pyridine.
20. Some alcohols undergo rearrangement or other unwanted side reactions when they dehydrate in acid. Alcohols may be dehydrated under mildly basic conditions using phosphorus oxychloride (POCI3) in pyridine. The alcohol reacts with phosphorus oxychloride much like it reacts with tosyl chloride, displacing a chloride ion from phosphorus to give an alkyl dichlorophosphate ester. The dichlorophosphate group is an outstanding leaving group. Pyridine reacts as a base with the dichlorophosphate ester to give an E2 elimination. Propose a reasonable mechanism for the dehydration of 2- methylcyclohexanol by POCl3 in pyridine.
Organic Chemistry
8th Edition
ISBN:9781305580350
Author:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. Foote
Publisher:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. Foote
Chapter11: Ethers, Epoxides, And Sulfides
Section: Chapter Questions
Problem 11.41P: Aldehydes and ketones react with one molecule of an alcohol to form compounds called hemiacetals, in...
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Concept explainers
Reactions of Ethers
Ethers (R-O-R’) are compounds formed by replacing hydrogen atoms of an alcohol (R-OH compound) or a phenol (C6H5OH) by an aryl/ acyl group (functional group after removing single hydrogen from an aromatic ring). In this section, reaction, preparation and behavior of ethers are discussed in the context of organic chemistry.
Epoxides
Epoxides are a special class of cyclic ethers which are an important functional group in organic chemistry and generate reactive centers due to their unusual high reactivity. Due to their high reactivity, epoxides are considered to be toxic and mutagenic.
Williamson Ether Synthesis
An organic reaction in which an organohalide and a deprotonated alcohol forms ether is known as Williamson ether synthesis. Alexander Williamson developed the Williamson ether synthesis in 1850. The formation of ether in this synthesis is an SN2 reaction.
Question
Transcribed Image Text:20. Some alcohols undergo rearrangement or other unwanted side reactions when they
dehydrate in acid. Alcohols may be dehydrated under mildly basic conditions using
phosphorus oxychloride (POCI3) in pyridine. The alcohol reacts with phosphorus
oxychloride much like it reacts with tosyl chloride, displacing a chloride ion from
phosphorus to give an alkyl dichlorophosphate ester. The dichlorophosphate group is an
outstanding leaving group. Pyridine reacts as a base with the dichlorophosphate ester to
give an E2 elimination. Propose a reasonable mechanism for the dehydration of 2-
methylcyclohexanol by POCl 3 in pyridine.
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