Upload
vipin-arora
View
236
Download
1
Embed Size (px)
Citation preview
7/27/2019 Alcohols Phenols & ether
http://slidepdf.com/reader/full/alcohols-phenols-ether 1/10
11. Alcohols, Phenols and Ethers
Classification of alcohols and phenols: Mono, di, tri or polyhydric –
On the basis of hybridisation –
3C sp
– OH
Primary, secondary and tertiary Allylic alcohols
Benzylic alcohols
2C sp
– OH
Vinylic alcohol
Phenol
7/27/2019 Alcohols Phenols & ether
http://slidepdf.com/reader/full/alcohols-phenols-ether 2/10
Classification of ethers:
Simple or symmetrical – C2H5OC2H5, C6H5OC6H5
Mixed or unsymmetrical –
C2H5OCH3, CH3OC6H5
Common names of some phenols:
Alcohols and phenols:
Preparation of alcohols –
From alkenes Acid catalysed hydration
[According to Markovnikov’s rule]
Hydroboration – oxidation
7/27/2019 Alcohols Phenols & ether
http://slidepdf.com/reader/full/alcohols-phenols-ether 3/10
From carbonyl compounds By reduction of aldehydes and ketones.
Aldehydes give 1 and ketones give 2 alcohols.Pd
2 2RCHO H RCH OH
By reduction of carboxylic acids and esters4
2
i LiAlH
2ii H O
catalyst
2 2catalystic hydrogenation
RCOOH RCH OH
RCOOR H RCH OH R OH
From Grignard reagents
Methanol gives 1 , other aldehydes give 2 , and ketones give 3 alcohols.
Preparation of phenols – From haloarenes
From benzenesulphonic acid
7/27/2019 Alcohols Phenols & ether
http://slidepdf.com/reader/full/alcohols-phenols-ether 4/10
From diazonium salts
From cumene
Physical properties of alcohols and phenols – Boiling points:
The boiling points of alcohols and phenols increase with increase in number
of carbon atoms as it involves increase in van der Waals forces. The boiling points of alcohols decrease with increase of branching. This is
because van der Waals forces decrease with decrease in surface area. Solubility:
Alcohols and phenols form H-bonds, so they are soluble in water. Their solubility decreases with increase in size of alkyl/aryl groups.
Chemical reactions: Alcohols react both as nucleophiles and electrophiles
Reactions that involve cleavage of O – H bond Acidity of alcohols and phenols
Reaction with metals
22ROH 2Na 2R O Na H
Sodium
alkoxide
7/27/2019 Alcohols Phenols & ether
http://slidepdf.com/reader/full/alcohols-phenols-ether 5/10
Acidity of alcoholsThe increasing order of acidity of alcohols is
Acidity of phenolsPhenols are more acidic than alcohols and water.Electron-withdrawing groups increase the acidity of phenols whileelectron-releasing groups decrease the acidity of phenols.
EsterificationPyridine
R/ArOH R COCl R/ArOCOR HCl Acetylation of salicylic acid
Reactions that involve cleavage of C – O bond in alcohols Reaction with hydrogen halide
2ROH HX RX H O
Lucas test – Used for distinguishing between 1°, 2° and 3° alcohols.(Lucas reagent – Concentrated HCl and ZnCl2)
Reaction with phosphorus trihalide
3 3 33R OH PX 3R X H PO X Cl,Br
7/27/2019 Alcohols Phenols & ether
http://slidepdf.com/reader/full/alcohols-phenols-ether 6/10
Dehydration
Treated with concentrated H2SO4 or H3PO4 or Anhyd. ZnCl2, or Al2O3
The order of increasing reactivity towards dehydration is
1 alcohol < 2 alcohol < 3 alcohol Oxidation (also known as dehydrogenation)
It involves formation of a carbon – oxygen double bond. Oxidising agent – Acidified KMnO4
directlyAlcohol Carboxylic acid
Oxidising agent Anhyd. CrO3
1 alcohol Aldehydealcohol Ketone
Pyridinium chlorochromate (PCC)
1 alcohol Aldehyde
Oxidising agent Heated Cu at 573 K
1 alcohol Aldehyde
alcohol Ketone
3 alcohols do not undergo oxidation
Reactions of phenols: Electrophilic aromatic substitution reaction
Nitration
The o-isomer is steam volatile due to intramolecular H-bondingwhile the p-isomer is less volatile due to intermolecular H-bonding.So, they can be separated by steam distillation.
7/27/2019 Alcohols Phenols & ether
http://slidepdf.com/reader/full/alcohols-phenols-ether 7/10
Halogenation
Kolbe’s reaction
Reimer – Tiemann reaction
Reaction of phenol with zinc dust
7/27/2019 Alcohols Phenols & ether
http://slidepdf.com/reader/full/alcohols-phenols-ether 8/10
Oxidation
Ethers:
Preparation of ethers – By dehydration of alcohols
Williamson synthesis
But in case of 2 and 3 halides, instead of substitution, elimination takesplace, resulting in alkenes.
Phenols are converted into ethers.
Physical properties of ethers – Boiling points:
7/27/2019 Alcohols Phenols & ether
http://slidepdf.com/reader/full/alcohols-phenols-ether 9/10
The boiling points of ethers are lower than those of alcohols of comparablemolecular masses due to the presence of H-bonding in alcohols.
Chemical reactions of ethers:
Cleavage of C – O bond Least reactive; under drastic conditions with excess of hydrogen halides, theC – O bond is cleaved
The order of increasing reactivity of hydrogen halides isHCl < HBr < HI
Electrophilic substitution Halogenation
Friedel Craft’s alkylation
Friedel Craft’s acylation
7/27/2019 Alcohols Phenols & ether
http://slidepdf.com/reader/full/alcohols-phenols-ether 10/10
Nitration
Contribute to this Revision Note:
If you find anything of importance missing from this note, email it to us at [email protected] , and weadd it to this note under your name!