Chapter 11 Alcohols Phenols and Ethers Notes pdf
The compounds obtained by replacing one hydrogen atom from aliphatic hydrocarbons by hydroxyl group are alcohols whereas those obtained by replacing hydrogen atom of aromatic hydrocarbons are phenols.
The substitution of hydrogen atom in a hydrocarbon by an alkoxy ( RO ) or aryloxy ( ArO ) gives another class of compounds known as ethers.
Classification of alcohols:
The alcohols are classified as Primary , secondary and tertiary alcohols depending upon the hydroxyl group attached to a primary, secondary or a tertiary carbon atom.
Allylic, vinylic and benzylic alcohols
Nomenclature of alcohols:
Nomenclature of Phenols:
Methods of Preparation of alcohols
1. From haloalkanes
Haloalkanes when boiled with aqueous KOH or moist silver oxide ( AgOH ) give alcohols.
2.By reduction of aldehydes , ketones and carboxylic acids
Aldehydes give primary alcohols and ketones give secondary alcohols by reduction with common reducing agents.
Reduction of aldehydes :
3. From Grignard's reagent
Grignard's reagent RMgX reacts with aldehydes, ketones and esters to form addition products which decompose with dil. HCl or dil. sulphuric acid to give alcohols.
- formaldehyde give primary alcohol
- other aldehydes give secondary alcohols
- ketones give tertiary alcohols
4. From alkenes
a) By acid catalysed hydration of alkenes
Alkenes add a molecule of water in the presence of mineral acids as catalyst to form alcohol.
Mechanism of this reaction is very important : Watch the video for mechanism
b) Hydroboration oxidation reduction
Alkenes react with diborane B2H6 to form trialkylboranes which upon treatment with alkaline hydrogen peroxide gives alcohols. This addition occurs according to anti Markovnikov's rule.
Methods of Preparation of Phenols
1. From diazonium Salts
On warming aqueous solution of diazonium salt it gives phenols.
2. From benzene sulphonic acid
First benzene is sulphonated with oleum to form benzene sulphonic acid then benzene sulphonic acid so formed is converted to sodium phenoxide by heating with sod. hydroxide. This on acidification gives phenol.
3. From chlorobenzene ( Dows Process )
4. From Cumene ( isopropyl benzene )
Cumene is prepared by Friedel craft alkylation of benzene with propene in the presence of phosphoric acid.
Cumene is first oxidised and then hydrolysed to give phenol.
5. From benzene ( Raschig's process )
First benzene is converted to chlorobenzene by using vapours of HCl in the presence of catalyst and excess of air. Then steam is passed through chlorobenzene in the presence of silica as catalyst to give Phenols.
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