A Alcohols are formed when a hy OH group. Examples: CH 3 OH, C 2 Phenols are formed when a hy OH group. Example: C 6 H 5 OH The substitution of a hydrogen O/Ar–O) yields another class of (dimethyl ether). Class Monohydric: CH 3 OH Methyl a Phenol Dihydric: Ethyle Trihydric: Class- XII Chemistry Chapter-11 Alcohols, Phenols and Ethers Alcohols ydrogen atom in a hydrocarbon, alipha 2 H 5 OH Phenols ydrogen atom in a hydrocarbon, aroma Ethers atom in a hydrocarbon by an alkoxy o f compounds known as ‘ethers’, for exa sification of Alcohols and Phenols alcohol, C 2 H 5 OH-Ethyl alcohol ene Glycol atic is replaced by – atic is replaced by – or aryloxy group (R– ample, CH 3 OCH 3
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Alcohols, Phenols and Ethers
Alcohols are formed when a hydrogen atom in a hydrocarbon, aliphatic is replaced by
OH group. Examples: CH3OH, C2
Phenols are formed when a hydrogen atom in a hydrocarbon,
OH group. Example: C6H5OH
The substitution of a hydrogen atom in a hydrocarbon by an alkoxy or aryloxy group (R
O/Ar–O) yields another class of compounds known as ‘ethers’, for example, CH
(dimethyl ether).
Classificati
Monohydric: CH3OH Methyl alcohol,
Phenol
Dihydric:
Ethylene Glycol
Trihydric:
Class- XII
Chemistry
Chapter-11
Alcohols, Phenols and Ethers
Alcohols
Alcohols are formed when a hydrogen atom in a hydrocarbon, aliphatic is replaced by
2H5OH
Phenols
Phenols are formed when a hydrogen atom in a hydrocarbon, aromatic is replaced by
Ethers
The substitution of a hydrogen atom in a hydrocarbon by an alkoxy or aryloxy group (R
O) yields another class of compounds known as ‘ethers’, for example, CH
Classification of Alcohols and Phenols
OH Methyl alcohol, C2H5OH-Ethyl alcohol
Ethylene Glycol
Alcohols are formed when a hydrogen atom in a hydrocarbon, aliphatic is replaced by –
aromatic is replaced by –
The substitution of a hydrogen atom in a hydrocarbon by an alkoxy or aryloxy group (R–
O) yields another class of compounds known as ‘ethers’, for example, CH3OCH3
Glycerol
Classification according to the hybridisation of the carbon atom to which the hydroxyl
group is attached.
(i) Compounds containing C
Alkyl Alcohol
Primary, secondary and tertiary alcohols
Allylic alcohols:
Benzylic alcohols:
Glycerol
Classification according to the hybridisation of the carbon atom to which the hydroxyl
Compounds containing Csp3-OH bond:
Primary, secondary and tertiary alcohols
Classification according to the hybridisation of the carbon atom to which the hydroxyl
(ii) Compounds containing Csp2- OH bond
Classification of Ethers
Simple or symmetrical if the alkyl or aryl groups attached to the oxygen atom are the
same. Example Diethyl ether, C2H5OC2H5
Mixed or unsymmetrical if the two groups are different.
C2H5OCH3 and C2H5OC6H5 are unsymmetrical ethers.
Preparation of Alcohols
1.From alkenes:
(i) By acid catalysed hydration:
Mechanism The mechanism of the reaction involves the following three steps:
Step 1:
Protonation of alkene to form carbocation by electrophilic attack of H3O+.
(ii)By hydroboration–oxidation:
2.From carbonyl compounds
(i) By reduction of aldehydes and ketones
oxidation:
2.From carbonyl compounds
By reduction of aldehydes and ketones:
The usual catalyst is a finely divided metal such as platinum(Pt), palladium(Pd) or
nickel (Ni). It is also prepared by treating aldehydes and ketones with sodium
borohydride (NaBH4) or lithium aluminium hydride (LiAlH4)
(iii) By reduction of carboxylic acids and esters:
3. From Grignard reagents:
Alcohols are produced by the reaction of Grignard reagents with aldehydes and
ketones.
Preparation of Phenols
1. From haloarenes:
Chlorobenzene is fused with NaOH at 623K and 3
is obtained by acidification of sodium phenoxide so produced.
2. From benzene sulphonic acid:
Benzene is sulphonated with oleum and benzene sulphonic acid so formed is
converted to sodium phenoxide on heating with molten sod
Acidification of the sodium salt gives phenol.
Alcohols are produced by the reaction of Grignard reagents with aldehydes and
Chlorobenzene is fused with NaOH at 623K and 320 atmospheric pressure. Phenol
is obtained by acidification of sodium phenoxide so produced.
From benzene sulphonic acid:
Benzene is sulphonated with oleum and benzene sulphonic acid so formed is
converted to sodium phenoxide on heating with molten sodium hydroxide.
Acidification of the sodium salt gives phenol.
Alcohols are produced by the reaction of Grignard reagents with aldehydes and
20 atmospheric pressure. Phenol
Benzene is sulphonated with oleum and benzene sulphonic acid so formed is
ium hydroxide.
3. From diazonium salts
4. From cumene
From cumene Phenol is manufactured from the hydrocarbon, cumene. Cumene
(isopropyl benzene) is oxidised in the presence of air to cumene hydroperoxide. It is
converted to phenol and acetone by treating it with dilute acid. Acetone, a by-
product of this reaction, is also obtained in large quantities by this method.
Physical Properties of Alcohol and Phenol
Boiling Points
The boiling points of alcohols and phenols increase with increase in the number of
carbon atoms (increase in van der Waals forces). In alcohols, the boiling points
decrease with increase of branching in carbon chain (because of decrease in van
der Waals forces with decrease in surface area).
Boiling points of alcohols and phenols are higher in comparison to other classes of
compounds, namely hydrocarbons, ethers, haloalkanes and haloarenes of
comparable molecular masses.
The high boiling points of alcohols are mainly due to the prese
hydrogen bonding in them which is lacking in ethers and hydrocarbons
Solubility
Solubility of alcohols and phenols in water is due to their ability to form
hydrogen bondwith water molecules.
Chemical Properties of A
Alcohols are versatile compounds. They react both as nucleophiles and electrophiles.
i) The bond between O–
(a) Reactions involving cleavage of O
1. Acidic nature of alcohols and phenols:
Acidic nature of alcohols:
The high boiling points of alcohols are mainly due to the presence of intermolecular
hydrogen bonding in them which is lacking in ethers and hydrocarbons
Solubility of alcohols and phenols in water is due to their ability to form
water molecules.
cal Properties of Alcohol and Phenol
Alcohols are versatile compounds. They react both as nucleophiles and electrophiles.
–H is broken when alcohols react as nucleophiles.
Reactions involving cleavage of O–H bond
Acidic nature of alcohols and phenols:
nce of intermolecular
hydrogen bonding in them which is lacking in ethers and hydrocarbons.
Solubility of alcohols and phenols in water is due to their ability to form
Alcohols are versatile compounds. They react both as nucleophiles and electrophiles.
H is broken when alcohols react as nucleophiles.
Alcohols react with sodium to form a salt (sodium
Acidic nature of phenols:
Reason
The hydroxyl group, in phenol is directly attached to the sp2 hybridised carbon
of benzene ring which acts as an ele
charge distribution in phenol molecule, as depicted in its resonance structures,
causes the oxygen of
to form a salt (sodium alkoxide) and hydrogen gas
The hydroxyl group, in phenol is directly attached to the sp2 hybridised carbon
of benzene ring which acts as an electron withdrawing group.
charge distribution in phenol molecule, as depicted in its resonance structures,
causes the oxygen of –OH group to be positive.
alkoxide) and hydrogen gas
The hydroxyl group, in phenol is directly attached to the sp2 hybridised carbon
ctron withdrawing group. Due to this, the
charge distribution in phenol molecule, as depicted in its resonance structures,
(iv) Comparison between acidity of phenol with ethanol.
Phenols are stronger acids than
(i)The reaction of phenol with aqueous sodium hydroxide indicates that phenols are
stronger acids than alcohols and water.
(ii) The ionisation of an alcohol and a phenol
Due to the higher electronegativity of sp2 hybridised carbon of p
attached, electron density decreases on oxygen. This increases the polarity of O
and results in an increase in ionisation of phenols than that of alcohols.
(iii) The stabilities of alkoxide and phenoxide ions
In alkoxide ion, the negative charge is localised on oxygen while in phenoxide ion, the
charge is delocalised. The delocalisation of negative charge makes phenoxide ion more
stable and favours the ionisation of phenol.
omparison between acidity of phenol with ethanol.
Phenols are stronger acids than alcohols because:
(i)The reaction of phenol with aqueous sodium hydroxide indicates that phenols are
stronger acids than alcohols and water.
(ii) The ionisation of an alcohol and a phenol
Due to the higher electronegativity of sp2 hybridised carbon of phenol to which
attached, electron density decreases on oxygen. This increases the polarity of O
and results in an increase in ionisation of phenols than that of alcohols.
(iii) The stabilities of alkoxide and phenoxide ions:
the negative charge is localised on oxygen while in phenoxide ion, the
charge is delocalised. The delocalisation of negative charge makes phenoxide ion more
stable and favours the ionisation of phenol.
(i)The reaction of phenol with aqueous sodium hydroxide indicates that phenols are
henol to which –OH is
attached, electron density decreases on oxygen. This increases the polarity of O–H bond
and results in an increase in ionisation of phenols than that of alcohols.
the negative charge is localised on oxygen while in phenoxide ion, the
charge is delocalised. The delocalisation of negative charge makes phenoxide ion more
2. Esterification
Alcohols and phenols react with ca
form esters.
Alcohols react with carboxylic acids to form esters
The reaction with carboxylic acid and acid anhydride is carried out in the presence of a
small amount of concentrated sulphuric acid. The
water is removed as soon as it is formed
Alcohols react with acid chlorides to form esters
The reaction with acid chloride is carried out in the presence of a base (pyridine) so as to
neutralise HCl which is formed during the reaction. It shifts the equilibrium to the right
hand side.
Phenols react acid anhydrides to form esters
Alcohols and phenols react with carboxylic acids, acid chlorides and acid anhydrides to
Alcohols react with carboxylic acids to form esters
The reaction with carboxylic acid and acid anhydride is carried out in the presence of a
small amount of concentrated sulphuric acid. The reaction is reversible, and therefore,
water is removed as soon as it is formed
Alcohols react with acid chlorides to form esters.
The reaction with acid chloride is carried out in the presence of a base (pyridine) so as to
rmed during the reaction. It shifts the equilibrium to the right
Phenols react acid anhydrides to form esters
rboxylic acids, acid chlorides and acid anhydrides to
The reaction with carboxylic acid and acid anhydride is carried out in the presence of a
reaction is reversible, and therefore,
The reaction with acid chloride is carried out in the presence of a base (pyridine) so as to
rmed during the reaction. It shifts the equilibrium to the right-
Phenols react with carboxylic acids to form esters
Phenols react with acid chlorides to form esters
Acetylation (formation of Aspirin
The introduction of acetyl (CH3CO) group in alcohols or phenols is known as acetylation.
Acetylation of salicylic acid produces aspirin.
(b) Reactions involving cleavage of carbon
1. Reaction with hydrogen halides
halides.
Phenols react with carboxylic acids to form esters
henols react with acid chlorides to form esters
irin)
The introduction of acetyl (CH3CO) group in alcohols or phenols is known as acetylation.
Acetylation of salicylic acid produces aspirin.
(b) Reactions involving cleavage of carbon – oxygen (C–O) bond in alcohols
Reaction with hydrogen halides: Alcohols react with hydrogen halides to form alkyl
The introduction of acetyl (CH3CO) group in alcohols or phenols is known as acetylation.
O) bond in alcohols
Alcohols react with hydrogen halides to form alkyl
ROH + HX → R–X + H2O
Lucas test
Lucas test is used to differentiate and categorize primary, secondary and tertiary alcohols
using a solution of anhydrous zinc chloride (ZnCl2) in concentrated hydrochloric acid (HCl).
This solution is commonly referred to as the Lucas reagent.
Primary
Alcohol
The solution remains colourless unless it is subjected to
heat. The solution forms an oily layer when heated.
Example: 1-Pentanol.
Secondary
Alcohol
The solution turns turbid and forms an oily layer in three to
five minutes (varies based on the solubility). Example: 2-
Pentanol.
Tertiary
Alcohol
The solution turns turbid and forms an oily layer
immediately. Example: 2-methyl-2-butanol.
2. Reaction with phosphorus trihalides: Alcohols are converted to alkyl bromides by
reaction with phosphorus tribromide.
3. Dehydration: Alcohols undergo dehydration (removal of a molecule of water) to form
alkenes on treating with a protic acid e.g., concentrated H2SO4 or H3PO4, or catalysts such
as anhydrous zinc chloride or alumina.
Thus, the relative ease of dehydration of alcohols follows the following order:
Tertiary
Mechanism of Dehydration of alcohols:
5. Oxidation: Oxidation of alcohols involves the formation of a carbon oxygen double
bond with cleavage of an O
Thus, the relative ease of dehydration of alcohols follows the following order:
Tertiary >Secondary > Primary
Mechanism of Dehydration of alcohols:
: Oxidation of alcohols involves the formation of a carbon oxygen double
bond with cleavage of an O-H and C-H bonds. Such a cleavage and formation of
Thus, the relative ease of dehydration of alcohols follows the following order:
: Oxidation of alcohols involves the formation of a carbon oxygen double
H bonds. Such a cleavage and formation of
bonds occur in oxidation reactions. These are also known as dehydrogenation
reactions as these involve loss of dihydrogen from an alcohol molecule.
Strong oxidising agents: KMnO4
Mild oxidising agents: CrO3 in anhydrous medium, pyridinium chlorochromate (PCC), a
complex of chromium trioxide with pyridine and HCl.
bonds occur in oxidation reactions. These are also known as dehydrogenation
ve loss of dihydrogen from an alcohol molecule.
: KMnO4
: CrO3 in anhydrous medium, pyridinium chlorochromate (PCC), a
complex of chromium trioxide with pyridine and HCl.
bonds occur in oxidation reactions. These are also known as dehydrogenation
ve loss of dihydrogen from an alcohol molecule.
: CrO3 in anhydrous medium, pyridinium chlorochromate (PCC), a
(c) Reactions of phenols
1. Electrophilic aromatic substitution:
(i) Nitration: With dilute nitric acid at low temperature (298 K), phenol yields a mixture of
ortho and para nitrophenols.
The ortho and para isomers can be separated by steam distillation.
o-Nitrophenol is steam volatile du
p-nitrophenol is less volatile due to intermolecular hydrogen bonding which causes the
association of molecules.
Formation of Picric acid (2,4,6-
(i)
Phenol phenol-2,4-disulphonic acid
ilic aromatic substitution:
With dilute nitric acid at low temperature (298 K), phenol yields a mixture of
The ortho and para isomers can be separated by steam distillation.
Nitrophenol is steam volatile due to intramolecular hydrogen bonding.
nitrophenol is less volatile due to intermolecular hydrogen bonding which causes the
-trinitrophenol) from phenol:
sulphonic acid Picric acid
With dilute nitric acid at low temperature (298 K), phenol yields a mixture of
e to intramolecular hydrogen bonding.
nitrophenol is less volatile due to intermolecular hydrogen bonding which causes the
Picric acid
(ii)
Phenol
(ii) Halogenation:
(a) When the reaction is carried out in solvents of low polarity such as CHCl3 or CS2
and at low temperature, monobromophenols are formed.
In non-aqueous medium
(b) When phenol is treated
white precipitate.
In aqueous medium
2. Kolbe’s reaction:
Phenoxide ion generated by treating phenol with sodium hydroxide is even more reactive
than phenol towards electrophilic aromatic substituti
substitution with carbon dioxide, a weak electrophile. Ortho hydroxybenzoic acid is
formed as the main reaction product.
Picric acid
When the reaction is carried out in solvents of low polarity such as CHCl3 or CS2
and at low temperature, monobromophenols are formed.
with bromine water, 2,4,6-tribromophenol is formed as
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.
When the reaction is carried out in solvents of low polarity such as CHCl3 or CS2
tribromophenol is formed as
Phenoxide ion generated by treating phenol with sodium hydroxide is even more reactive
on. Hence, it undergoes electrophilic
substitution with carbon dioxide, a weak electrophile. Ortho hydroxybenzoic acid is
3. Reimer-Tiemann reaction:
On treating phenol with chloroform in the presence of sodium hydro
introduced at ortho position of benzene ring. This reaction is known as Reimer
reaction. The intermediate substituted benzal chloride is hydrolysed in the presence of
alkali to produce salicylaldehyde.
4. Reaction of phenol with zinc dust:
Phenol is converted to benzene on heating with zinc dust.
5.Oxidation:
Oxidation of phenol with chromic acid produces a conjugated diketone known as
benzoquinone.
On treating phenol with chloroform in the presence of sodium hydro
introduced at ortho position of benzene ring. This reaction is known as Reimer
reaction. The intermediate substituted benzal chloride is hydrolysed in the presence of
alkali to produce salicylaldehyde.
l with zinc dust:
Phenol is converted to benzene on heating with zinc dust.
Oxidation of phenol with chromic acid produces a conjugated diketone known as
On treating phenol with chloroform in the presence of sodium hydroxide, a –CHO group is
introduced at ortho position of benzene ring. This reaction is known as Reimer - Tiemann
reaction. The intermediate substituted benzal chloride is hydrolysed in the presence of
Oxidation of phenol with chromic acid produces a conjugated diketone known as
In the presence of air, phenols are slowly oxidised to dark coloured mixtures containing
quinones.
(i) By dehydration of alcohols:
Ethanol is dehydrated to ethene in the presence of sulphuric acid at 443 K. At 413 K,
ethoxyethane is the main product.
2. Williamson synthesis:
It is an important laboratory method for the preparation of symmetrical and
unsymmetrical ethers. In this method, an alkyl halide is allowed to react with sodium
alkoxide.
(i)
In the presence of air, phenols are slowly oxidised to dark coloured mixtures containing
Preparation of Ethers
Ethanol is dehydrated to ethene in the presence of sulphuric acid at 443 K. At 413 K,
xyethane is the main product.
It is an important laboratory method for the preparation of symmetrical and
unsymmetrical ethers. In this method, an alkyl halide is allowed to react with sodium
In the presence of air, phenols are slowly oxidised to dark coloured mixtures containing
Ethanol is dehydrated to ethene in the presence of sulphuric acid at 443 K. At 413 K,
It is an important laboratory method for the preparation of symmetrical and
unsymmetrical ethers. In this method, an alkyl halide is allowed to react with sodium
(ii)
Ethers containing substituted alkyl groups (secondary or tertiary) may also be prepared by
this method. The reaction involves SN2 attack of an alkoxide ion on primary alkyl halide.
Phenols are also converted to ethers by this method.
ining substituted alkyl groups (secondary or tertiary) may also be prepared by
this method. The reaction involves SN2 attack of an alkoxide ion on primary alkyl halide.
Phenols are also converted to ethers by this method.
ining substituted alkyl groups (secondary or tertiary) may also be prepared by
this method. The reaction involves SN2 attack of an alkoxide ion on primary alkyl halide.
Physical properties of Ethers:
Boiling point:
Boiling points of Ethers are lower than alcohols. The large difference in boiling points of
alcohols and ethers is due to the presence of hydrogen bonding in alcohols.
Solubility:
The miscibility of ethers with water resembles those of a
mass. This is due to the fact that just like alcohols, oxygen of ether can also form
hydrogen bonds with water molecule
Chemical properties of Ethers:
1.Cleavage of C–O bond in ethers
The reaction of dialkyl ether gives t
Ethers with two different alkyl groups are also cleaved in the same manner.
Boiling points of Ethers are lower than alcohols. The large difference in boiling points of
alcohols and ethers is due to the presence of hydrogen bonding in alcohols.
The miscibility of ethers with water resembles those of alcohols of the same molecular
mass. This is due to the fact that just like alcohols, oxygen of ether can also form
hydrogen bonds with water molecule.
Chemical properties of Ethers:
O bond in ethers:
The reaction of dialkyl ether gives two alkyl halide molecules.
Ethers with two different alkyl groups are also cleaved in the same manner.
Boiling points of Ethers are lower than alcohols. The large difference in boiling points of
alcohols and ethers is due to the presence of hydrogen bonding in alcohols.
lcohols of the same molecular
mass. This is due to the fact that just like alcohols, oxygen of ether can also form
Ethers with two different alkyl groups are also cleaved in the same manner.
Alkyl aryl ethers are cleaved at the alkyl
bond. The reaction yields phenol and alkyl halide.
When one of the alkyl group is a tertiary group, the halide formed is a tertiary halide.
It is because in step 2 of the reaction, the departure of leaving group (HO
more stable carbocation [(CH3)3C
Alkyl aryl ethers are cleaved at the alkyl-oxygen bond due to the more stable aryl
bond. The reaction yields phenol and alkyl halide.
ne of the alkyl group is a tertiary group, the halide formed is a tertiary halide.
It is because in step 2 of the reaction, the departure of leaving group (HO
more stable carbocation [(CH3)3C+], and the reaction follows SN1 mechanism
oxygen bond due to the more stable aryl-oxygen
ne of the alkyl group is a tertiary group, the halide formed is a tertiary halide.
It is because in step 2 of the reaction, the departure of leaving group (HO–CH3) creates a
], and the reaction follows SN1 mechanism
2. Electrophilic substitution:
the alkoxy group (-OR) is ortho, para directing and activates the aromatic ring towards
electrophilic substitution.
(i) Halogenation:
(ii) Friedel-Crafts reaction:
(iii) Nitration:
Anisole reacts with a mixture of conc
of ortho and para nitro anisole.
OR) is ortho, para directing and activates the aromatic ring towards
Anisole reacts with a mixture of concentrated sulphuric and nitric acids to yield a mixture
of ortho and para nitro anisole.
OR) is ortho, para directing and activates the aromatic ring towards
entrated sulphuric and nitric acids to yield a mixture