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  1. >>Class 12
  2. >>Chemistry
  3. >>Alcohols, Phenols and Ethers
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Alcohols, Phenols And Ethers

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1

Dehydration of alcohols at different temperature

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At 443K concentrated sulphuric acid  and alcohol produces alkene.
At 413 K concentrated sulphuric acid and alcohol produces ether.
 
Name the reagents used in the following reaction:
Dehydration of propan-2-ol to propene.
2

Reaction between ethers and halogens acids

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Ethers are easily cleaved by hydroiodic acid or hydrobromic acid.

The cleavage of C-O bond in ethers takes place under drastic conditions with excess of hydrogen halides. The reaction of dialkyl ether gives two alkyl halide molecules.

Alkyl aryl ethers are cleaved at the alkyl-oxygen bond due to the more stable aryl-oxygen bond. The reaction yields phenol and alkyl halide.

Define ether. What is the action of hot hydroiodic acid on isopropyl methyl ether?
3

Kolbe's reaction of phenols

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Phenoxide ion generated by treating phenol with sodium hydroxide is even more reactive than phenol towards electrophilic aromatic substitution. Hence, it undergoes electrophilic substitution with carbon dioxide, a weak electrophile. Ortho hydroxybenzoic acid is formed as the main reaction product.
Phenol on treatment with in the presence of NaOH followed by acidification produces compound X as the major product. X on treatment with in the presence of catalytic amount of produces:
4

Hydroboration-oxidation reactions of alkenes

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The addition of borane to the double bond takes place in such a manner that the boron atom gets attached to the sp2 carbon carrying greater number of hydrogen atoms. The alcohol so formed looks as if it has been formed by the addition of water to the alkene in a way opposite to the Markovnikovs rule. In this reaction, alcohol is obtained in excellent yield.
What is meant by hydroboration-oxidation reaction? Illustrate it with an example.