Download Alcohols phenols ethers

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Alcohols are the hydroxyl derivatives of aliphatic hydrocarbon in which the –OH group
is attached to alkyl group.
→
R-H
R-OH
CH4
→
C2H6
→
CH3OH
(Methanol)
C2H5OH
(Ethanol)
The aromatic hydroxyl compounds in which one or more hydroxyl groups are directly
attached the aromatic nucleus (i.e. benzene like ring) are called Phenols.
Ph -H
→
Ph-OH
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,
CH3OCH3 (dimethyl ether). ethers as compounds formed by substituting the hydrogen
atom of hydroxyl group of an alcohol or phenol by an alkyl or aryl group.
Alcohols are organic compounds that have one or more hydroxy (-OH) groups bonded to
the carbon atoms in aliphatic compounds. They occur widely in nature and have many
industrial and pharmaceutical applications. For example, methanol and ethanol are two
industrially important alcohols.
+OR
R-H
→
R-O-R
Nomenclature of Alcohols
The general formula of monohydric alcohols is C nH2n+1OH where n=1, 2, 3……….etc..
or R-OH where R is any alkyl group .These are named by the following systems.
(i) common system: In the common system, monohydric alcohols are called alkyl
alcohols their names are derived by adding the word alcohol to the name of the alkyl
group present in the molecule.
(ii) carbinol system: In this system, methyl alcohol (CH3OH) is called carbinol while
other alcohols are named as alkyl or aryl derivatives of carbinol.
(iii) IUPAC system: Alcohols are named by replacing ‘e’ in the name of parent alkane
by ‘ol’. The IUPAC and common names for several alcohols are given below
Structure
CH3OH
CH3CH2OH
CH3CH2CH2OH
Common
methyl alcohol
ethyl alcohol
n-propyl alcohol
IUPAC
Methanol
Ethanol
Propan-1-ol
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Among the compounds with carbon-oxygen single bond are the classes of alcohols, phenols and
ethers having the following general structures.
Alcohols and Hydrogen Bonding
The differences in physical properties between
alcohols and alkanes1. Alcohols have higher boiling points
than alkanes of similar molecular mass.
2. Alcohols have much higher solubility in water
than alkanes of similar molecular mass.
Figure shows the association of ethanol molecules in
the liquid state (only two of the three possible
hydrogen bonds to the upper oxygen are shown here).
Alcohols have higher boiling points and are more soluble in water than hydrocarbons.
STRUCTURE
In alcohols, oxygen atoms are sp3 hybridized. Two of the four sp3 hybridized orbitals of
oxygen get involved in formation of σ-bond with hydrogen and carbon respectively In
alcohols, both carbon and where as rest of two sp3 hybridized orbitals contain lone pair of
electrons. C-O–H bond angle is found to be as 105o ( rather than normal tetrahedral
angle 109.5O) Deviation from normal angle can be explained on the basis of greater
repulsion by lone pairs than bond pairs.
CLASSIFICATION OF ALCOHOLS
On the basis of number of hydroxyl groups present in a molecule, alcohols are classified
as
(I) Monohydric alcohols : contain only one hydroxyl group in their molecules.
CH3 OH :
methyl alcohol
(CH3)3C- OH : Tert. butyl alcohol
(II) Dihydric alcohol
contain two hydroxyl groups situated on different carbon
atoms.it is also called diols or glycols
(iii) Trihydric alcohol
Compounds in which three hydrogen atoms are replaced by
three hydroxyl groups.
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CLASSIFICATION OF MONOHYDRIC ALCOHOLS
Monohydric alcohols are classified according to the type of hybridization of the carban
atom to which the hydroxyl group is attached.
1. Compound containing C sp3 – OH bond.
In these alcohols, the –OH group is attached to an sp3 –hybridized carbon atom
of an alkyl group.
(i) Primary alcohol(1o): In these alcohols, the hydroxyl group is attached with
primary (1o) carbon atom. The general formula is R-CH2-OH. R may be H or alkyl
group
(ii) Secondary alcohol (2o): In these alcohol attached with secondary (2o) carbon
atom. The general formula is
R and R’ may be same or different
(iii) Tertiary alcohol(3o): In these alcohols, the hydroxyl group is attached with,
tertiary (3o) carbon atom. General formula is
R, R’, R” may be same or different
iv) Allylic alcohol : In these alcohol, the –OH group is attached to an sp3 hybridized
carbon next to the carbon-carbon double bond. i.e. to an allylic carbon
(v)Benzylic alcohols: In these alcohols, the –OH group is attached to a sp3- hybridized
carbon atom next to an aromatic ring. It may be 10, 20 and 30.
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2
2. Compound containing C sp -OH bond
In these alcohols, the –OH group is attached to a carbon atom of double bond i.e.
vinylic carbon. These are also called vinylic alcohol.
CH2 = CH2 – OH (vinyl alcohol, unstable)
ISOMERISM IN ALCOHOLS
1. Chain isomerism : Alcohols containing four or more carbon atoms
exhibit chain isomerism in which the isomers differ in the chain of carbon atoms
attached to the hydroxyl group Molecular formula C4H9OH shows the following
isomers.
CH3 = CH2 – CH2 – CH2 – OH
CH3-CH-CH2CH3
( Butan – 1 –ol)
OH (Sec-Butyl alcohol)
CH3
CH3- C- OH
CH3
(tert-butyl alcohol)
2.Position isomerism : Alcohols containing three or more carbon atoms show
position isomerism in which the isomers differ in the position of hydroxyl group when
carbon chain is the same.
3.Functional group isomerism: Saturated monohydric alcohols containing
two or more carbon atom show functional isomerism with ethers e.g.
CH3 – CH2 – OH (ethanol ) and CH3 – O – CH3 ( methoxymethane)
Besides the structural isomerism, alcohols having asymmetric carbon atom
exhibit optical isomerism e.g.
GENERAL METHODS OF PREPARATION OF ALCOHOLS
1. Hydrolysis of alkyl halide:
Alkyl halides on heating with dilute aqueous alkali give corresponding alcohols. Better
yields are obtained when alkyl halides are heated with moist silver oxide.
∆
R-X + KOH (aq) →
R-OH + KX
(moist) Ag2O
R-X + AgOH
→
∆
R-OH + AgX
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This method is not satisfactory for preparing alcohol because haloalkanes are
themselves obtained from alcohols and in higher halides, the alkenes are formed as side
products However, satisfactory results are obtained by using moist silver oxides (AgOH)

(A) Primary (10) alkyl halides gives good yield of alcohols, while tertiary butyl
halides mainly give alkenes due to dehydrohalogenation







(B) Secondary(2o) alkylhalides gives a mixture of alcohol and alkene
Br
CH3-CH-CH3 +KOH
OH
∆
→
CH3-CH-CH3
+ CH2-CH=CH2
hydrolysis of 1o halides proceeds by SN2 mechanism while those of 3o halides by SN1
mechanism. The hydrolysis 2o alkyl halides may proceed by SN1 or SN2 mechanism
(2) Hydration of alkene :
The term hydration means addition of a molecule of water. The hydration of alkenes can
be carried out either indirectly or directly. In the indirect process, alkenes are passed
through con. H2SO4 to form alkyl hydrogen sulphates, These upon hydrolysis with
boiling water give alcohols. thus
1.Direct hydration
∆
CH2=CH2 + H2SO4 → CH3–CH2–OSO3H+H2O → CH3CH2OH + H2SO4
Ethene
ethyl hydrogen sulphate
Ehanol
HOH/∆
CH3-CH=CH2 + H-OSO3H → CH3-CH-CH3 →
CH3-CH-CH3 + H2SO4
Propene
OSO3H
isopropyl hydrogen sulphate
OH
Propan-2-ol
Mechanism:
The mechanism of acid catalysed addition of water (hydration) to alkenes involves
following stapes:
Step I : Electrophilic attack by hydronium ion (H3O+) on alkene gives an
intermediate carbocation
H2SO4 → H+ + HSO4-
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Step II: Nucleophilic attack by water on carbocation to yield protonated alcohol
Step III: Deprotonation ( loss of proton) to form an alcohol
Addition of H2SO4 follows Markownikoff’s rule
2.Indirect hydration
a) Oxymercuration - demercuration : Alkenens react with mercuric acetate
(CH3COO)2Hg or Hg(OAc)2, to form oxymercuration products which upon reduction
with NaBH4 in basic medium give demercuration product alcohols. thus,
Step-1:Oxymercuration
Step-2:Demercuration
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b) Hydroboration–Oxidation: Diborane (B2H6) is an electron deficient molecule
.Therefore, it acts as an electrophile and reacts with alkenes to form trialkylboranes
which upon subsequent oxidation with alkaline H2O2 give alcohols. Thus
Ether
R-CH=CH2
+
B2H6
→
RCH2-CH2-BH2
RCH2-CH2-BH2 + R-CH=CH2 → (RCH2CH2)2BH
(RCH2CH2)2BH + R-CH=CH2 → (RCH2CH2)3B
H2O2/OH-
(RCH2CH2)3B
→
3RCH2-CH2-OH + H3BO3
Reaction ultimately results in anti Markownikoff’s addition of water
(3)Hydrolysis of esters :
H+ or OH-
RCOOR’ +H2O
→
RCOOH + R’OH
(4)Hydrolysis of ethers:
H2SO4
R-O-R’ +
H-O-H
→
R-OH + R’-OH
(5)Action of nitrous acid (HONO) on primary amine:
Aliphatic primary amines on treatment with nitrous acid (NaNO2+HCl) give primary
alcohols.
RNH2 + HONO → R-OH + N2↑ + H2O
Or
Methylamine does not yield methyl alcohol only, but in excess of nitrous acid the other
products may be formed as, methyl nitrite or dimethyl ether.
CH3NH2 + 2HNO3 → CH3 – O – N = O + 2H2O + N2↑
Methyl nitrite
2CH3NH2 + 2HNO3 → CH3 – O – CH3 + 2H2O + N2↑
Dimethyl ether
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(6)Reduction of aldehydes and ketones:
Aldehyde and Ketones are reduced to the corresponding alcohols by (i)addition of H2 in
presence of catalyst (Catalytic hydrogenation),such as finely divided Pt, Pd, Ni, or
Ru,(ii) By nascent hydrogen obtained by the action of Na/C2H5OH and (iii)By complex
metal Hydrides such as LiAlH4 or NaBH4.
Catalysts : H2/Ni or Na/C2H5OH or LiAlH4 or NaBH4
Catalyst
HCHO
→ CH3OH
Catalyst
R-CHO
→ R-CH2-OH
pri alcohol
(7) Action of Grignard reagents: All the three types of the alcohols can be
prepared by this method. An aldehyde or Ketone undergoes nucleophilic addition of
Grignard reagent in presence of dry ether to form a complex which on acid hydrolysis
gives an alcohol. It occurs in two steps
Step I : Nucleophilic addition of Grignard reagent to the carbonyl group to form an
adduct
Step II : hydrolysis of adduct to yield alcohol
(I)Primary alcohol is produced with methane
(ii)Secondary alcohol is obtained with other aldehydes
(III)Tertiary alcohol is produced with ketones
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(8)Reduction of carbonyl group including carboxylic acid and esters:
Reduction of carboxylic acids with LiAlH4 or better with B2H6 gives primary alcohols.
Diborane, however, does not easily reduce functional groups such as ester, nitro
halo,etc.thus
LiAlH4 Or B2H6/ether
→
R-COOH
R-CH2-OH
LiAlH4
→
RCOCl
Acetyl chloride
R-CH2-OH + HCl
primary alcohols
LiAlH4
R(CO)2O
→
2R-CH2-OH
Acid anhydride
4
Reduction of carboxyl compounds and esters to alcohol by using alcoholic sodium
is called Bouveault – Blance reduction.
O
CH3-C-OC2H5
Na/alcohol
→
2CH3CH2OH
Ethyl alcohol
(9)From epoxides :
Epoxyalkanes such as oxiranes or Ethylene oxide react with Grignard reagent in the
presence of anhydrous ether to form addition products which are hydrolysed by water in
the presence of acid to form alcohols and on reduction in the presence of LiAlH4 gives
Alcohols.
(i)Reduction
(ii)Action of Grignard reagent
RMgX +
CH2-CH2 →
RCH2-CH2-OMgX
O
R-CH2-CH2-OH +Mg(OH)X
(10)Oxo process :
This reaction is also known as carbonylation or hydroformylation reaction
2CH2-CH=CH2+2CO+2H2
→
CH3CH2CH2-CHO
Cu-Zn(H2) or LiAlH4
CH3CH2CH2-CHO
→
CH3CH2CH2CH2OH
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(11)Fermentation of carbohydrates:
Ethanol or ethyl alcohol or grain alcohol can be prepared on commercial scale by the
fermentation of sugar (present in molasses and grapes etc) or starch (present in Rice,
berlay, maize etc).The reactions that are taking place are catalysed by certain enzymes
also called Biocatalysts.
(i)From Molasses
Molasses is the mother liquor after crystallization of sugar from sugar solution
Invertase
C12H22O11 + H2O
→
C6H12O6 +
C6H12O6
Glucose
fructose
Zymase
C6H12O6
→
2C2H5OH + CO2
Ethyl alcohol
(ii)From starch
Diatase
2(C6H10O5)n +nH2O
→
Maltase
nC11H22O11
→
2nC6H12O6
H2O
Zymase
C6H12O6
→ 2C2H5OH +CO2
(12) Reduction of water gas
It is an industrial method for preparation of methanol
PHYSICAL PROPERTIES OF ALCOHOLS
(i) Physical state
*At ordinary temperature, lower members upto C11 are colourless liquids. Higher
members are wax like solids The lower members have a characteristic smell and a
burning taste while higher members are almost colourless ,odourless waxy solids.
*Alcohol are lighter than water
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(iii) Boiling point
*Boiling points of alcohols are much higher than corresponding aliphatic hydrocarbons
and halo alkanes.
*Among isomeric alcohol, the boiling points decrease in the following
order
Primary > Secondary > tertiary
*The boiling point decreases with branching.
*The high boiling points of alcohol are mainly due to the presence of intermolecular
hydrogen bonding in them which is lacking in ether and hydrocarbons.
(iv) Solubility
*Alcohols can form hydrogen bonds with water and break H-bond between water
molecule.
*Lower alcohols are soluble in water due to hydrogen bonding but solubility
decreases with increase of molecular mass since hydrocarbon part increases which
interrupts the hydrogen bond formation.
*Solubility increases with branching since surface area of hydrocarbon part
decreases with increase of branching.
CHEMICAL PROPERTIES OF ALCOHOLS
Alcohols are versatile compounds. They react both as nucleophile and
electrophile

*Alcohol as nucleophile





*Alcohol as electrophile
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Chemical reactions of alcohols can be classified into following categories
(A) Reactions due to O-H bond, breaking
(B) Reactions due to C-OH bond breaking
(C) Reaction of alcohol molecule as a whole
(A)Reactions due to O-H bond, breaking
Order of ease of cleavage of O-H bond and thus order of reactivity is
CH3OH > primary > secondary> tertiary
1. Reaction with metals ( acidic nature):
2R – O – H + 2Na
→ 2R-O-Na +H2
Sodium alkoxide
Alcohols are stronger acid than acetylenes and acidic nature is in the order
H-OH > ROH> CH≡CH > NH3RH
Acidic character of alcohol and water
*Alcohols act as Bronsted acids which lose a proton to strong base 

*Electron releasing inductive effect (+I) of the alkyl group makes the alcohol weaker
acids than water. 






*On treating alkoxide ion with water, the starting alcohol is obtained
.
Comparison of acidic character of primary, secondary and tertiary alcohols The acidic
character of alcohols is due to the polar nature of O – H bond an electron releasing
group increases electron density on oxygen tending to decrease the polarity of O – H
bond. This decreases the acidic strength and so the acid strength of alcohol decreases in
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the following order
RCH2OH > R2CHOH > R3COH
Order of +I effect in various isomeric alcohols is
CH3OH < Primary < secondary < tertiary
2. Esterification :
*If the above reaction is carried out with dry HCl gas as catalyst, the reaction is known
as Fischer-Spcier esterification
*Order of reactivity of different alcohols towards esterification is
CH3OH > RCH2OH > R2CHOH > R3COH
*As the size of hydrocarbon part (R) around –OH increases, rate of reaction
decreases due to steric hinderance
3. Reaction with inorganic acid
H2O C2H5OH + HOSO2OH
→
C2H5SO3OH + H2O
Sulphuric acid
C2H5OH + HO-NO2
Nitric acid
ethyl hydrogen sulphate
→ C2H5-O-NO2 + H2O
ethyl nitrate
4. Acylation or reaction with acid chloride and acid anhydrides
*When alcohols reacts with acid chloride or acid anhydrides, the hydrogen of the
hydroxyl group is replaced by an acyl group (RCO-) resulting in the formation of
esters. The process is known as acylation 
*When the hydrogen of –OH group is replaced by CH3CO- (acetyl) group, the process
is termed acetylation. 
*The acetylation of alcohol is usually carried out in the presence of base such as
pyrimidine.
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(B) Reaction due to C – OH bond breaking
Order of ease of cleavage of C – OH bond and thus reactivity of different
alcohols is
Tertiary > Secondary > Primary > CH3OH
1. Reaction with halogen acids
R – OH + H – X → R-X +H2O
*For a given hydrogen halide order of reactivity of different alcohol is
*Allyl > benzyl > 3o > 2o > 1o
*Order of reactivity of HX is
HI > HBr > HCl
(i)With HClDue to low reactivity, the reactions of primary and secondary alcohols with HCl require
the use of some Lewis acid catalyst such as anhydrous zinc chloride. However, tertiary
alcohol react readily with conc. HCl even in the absence of a catalyst, i.e., anhydrous
ZnCl2.
Anhydrous ZnCl2
CH3CH2-OH + H-Cl
→
∆
CH3CH2-Cl +H2O
1-chloro ethane
CH3
CH3
Anhydrous ZnCl2
HC-OH
+
H-Cl
→
CH3
HC-Cl +H2O
CH3
2-chloroPropane
CH3
CH3
Anhydrous ZnCl2
CH3-C-OH + H-Cl
CH3
→
CH3- C-Cl + H2O
CH3
2-chloro-2-methylPropane
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(ii)With HBr-
Like HCl, the reaction of primary alcohols with constant boiling HBr (48%) is
carried out in presence of a small amount of conc. H2SO4 as catalyst. No catalyst is
required for secondary and tertiary alcohols because they undergo dehydration in
presence of conc. H2SO4 to give alkenes
Cocn.H2SO4
→
CH3-CH2-OH + HBr
CH3CH2-Br + H2O
reflux
(iii)With HI-Alkyl halides are formed, on refluxing alcohols with constant boiling HI (57%).
Reflux
→
CH3OH + HI
CH3-I +
H2O
However, when an alcohol is heated with HI in presence of red phosphorus, reduction
occurs to form the corresponding alkane.
Red P
CH3OH + 2HI
→
CH4 + H2O + I2
423K
2. Reaction with phosphorus halides and Thionyl chloride
Alcohols react with Thionyl chloride in presence of pyridine to form chloroalkanes or
alkyl chloride. Phosphorus halides such as PCl5, PCl3, PBr3 (P+Br2) and PI3(P+I2) react
with alcohols to form the corresponding haloalkanes or alkyl halides
R - OH +
PCl5
→
R-Cl
Chloro
alkane
3R - OH +
PCl3
alkane
PBr3
POCl3 + HCl
Phosphorus
Oxychloride
→ 3R-Cl + H3PO3
Chloro
3R - OH +
+
Phosphorus
acid
→ 3R-Br + H3PO3
Bromo
alkane
R - OH
+
SOCl2 →
R-Cl
+ SO2↑ + HCl
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3. Reaction of Nitric acid
When a mixture of the vapours of an alcohol and ammonia are passed over heated
alumina (Al2O3) at 633K, A mixture of Primary, secondary, and tertiary amine is
produced.
ROH +HONO2 →R-O-NO2 +H2O
Alkyl nitrite
Al2o3
ROH + NH3
→
RNH2 + H2O
10Amine
Al2o3
ROH + RNH2 →
R2NH + H2O
20Amine
Al2o3
ROH + R2NH
→
R3N +
H2 O
0
3 Amine
Al2o3
ROH + R3N
→
(R4N+)OH-
(R4N+)OH-: Quaternary alkyl ammonium hydroxide
(C) Reaction involving alcohol molecule as a whole
1. Dehydration
Dehydration (removal of a molecule of water)of alcohols can lead to the formation of either
alkenes or ethers.This dehydration can be carried out either with protonic acids such as conc.
H2SO4,H3PO3 or catalysts such as anhydrous zinc chloride or alumina.
(a)With protonic acids
Mechanism of dehydration
Step I: Formation of protonated alcohol
Step II : Formation of carbocation. It is the slowest step and hence the rate determining
step of the reaction
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Step III : Formation of ethene by elimination of proton
 * Formation of 2-methyl but-2-ene
Mechanism
In case of secondary and tertiary alcohols, Saytzeff’s rule is followed and the ease of
dehydration of alcohol is in the order
Tertiary > Secondary > Primary
(b) with heated Alumina (Al2O3):When vapours of an alcohol are passed over heated
alumina, different products are obtained at different temperature as given below.
(i) At 513- 523K , intermolecular dehydration takes place to form ethers
Al2O3
→
2C2H5OH
CH3CH2-O-CH2CH3 + H2O
513-523K
(ii) At 633K, intramolecular dehydration takes place to form Alkenes
Al2O3
C2H5OH
→
CH2=CH2 + H2O
623K
2. Dehydrohalogenation
(a)A primary alcohol loses hydrogen and forms aldehyde
Cu/573k
RCH2OH
→
RCHO + H2
(b) A secondary alcohol loses hydrogen and form a ketone
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Cu/573k
R2CHOH
→
( R )2C=O + H2
(c)A tertiary alcohol undergoes dehydration of alkene
Cu/573k
(CH3)3COH
→
(CH3)2C=CH2 + H2
3. Oxidation
(i) Primary alcohols on oxidation gives aldehydes which further get
oxidized to carboxylic acid
Oxidation can be stopped at aldehyde stage by using collin’s reagent
( CrO3∙2C5H5N, chloroform trioxide-pyridine complex) or pyridinium chlorochromate,
PCC ( CrO3 ∙ 2C5H5N∙HCl )
(ii) Secondary alcohols on oxidation give mixture of carboxylic acids
This oxidation can be stopped at ketone stage by using (CrO3)
(iii) A tertiary alcohol having no oxidisable hydrogen linked to carbon atom bearing
hydroxyl group, is stable to oxidation in neutral or alkaline KMnO4 solution
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4. Reaction with bleaching powder:
Chloroform was discovered by Libig in 1831 and named was given to Dumas. It can be
prepared by the action of aqueous paste of CaOCl (bleaching powder/Calcium
oxychloride) with ethanol. After completion of reaction chloroform distilled at 334 K and
it is dried over fused CaCl2.
Hydrolysis
CaOCl2 +
Oxidation
H2O
→
CH3CH2OH + Cl2 →
Ca(OH)2 + Cl2
CH3CHO + 2HCl
Chlorination
2CH3CHO + 3Cl2 →
CCl3CHO + 3HCl
Hydrolysis
2CCl3CHO + 3Ca(OH)2→ 2CHCl3 + (HCOO)2Ca
5. Haloform Reaction
Compound having at least one methyl group linked to the carbonyl carbon atom i.e., these
compounds are easily oxidized by sodium hypohalite solution (Cl2,Br2,I2 in the presence of dil
NaOH) to give Haloform (Chloroform, Bromoform or Iodoform ).
When the reaction is carried out with sodium hypoiodite NaOI (I2 +aq. NaOH), a yellow ppt. of
iodoform is produced.
heat
CH3CH2OH + 4I2 + 6 NaOH → CHI3 + 5NaI + HCOONa + 5H2O
Sodium Formate
This reaction like the preparation of chloroform also in three steps
Oxidation
C2H5OH
→
Iodination
CH3CHO
(NaOH+I2)
→
(NaOH)
hydrolysis
CI3CHO
→
I2
CHI3
CH3CHO + 3I2 → CI3CHO + 3HI
Acetaldehyde
CI3CHO + NaOH → CHI3 + HCOONa
Iodoform
(yellow ppt)
CH3COCH3 + I2 → CI3COCH3 + 3HI
CI3COCH3 + NaOH → CHI3 + CH3COONa
Acetone
place of iodine, bromine or chlorine can be taken when the corresponding compounds
bromoform or chloroform are to be formed. This reaction in general is known as
haloform reaction.
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SOME COMMERCIALLY IMPORTANT ALCOHOLS
1. Methanol (Wood Spirit or Wood naphtha)
*for the manufacture of formaldehyde which is widely used as a preservative for
biological specimens and in the manufacture of formaldehyde resins such as Bakelite,
melamine-formaldehyde, urea-formaldehyde, etc.
* for denaturing ethyl alcohol i.e., to make it unfit for drinking purposes, Denatured
alcohol is commonly known as methylated spirit.
*In the manufacture of perfumes, drugs and varnishes.
* as an antifreeze for automobile radiators.
* It is used as solvent in paints, varnishes and celluloid.
2. Ethanol (Spirit of Wine or Grain alcohol)
*Ethanol is produced by fermentation of molasses into glucose and
Fermentation gives ethanol and carbon dioxide
Invertase
C12H22O11 + H2O
→
C6H12O6 + C6H12O6
Glucose
fructose
Zymase
C6H12O6
→
2C2H5OH + CO2

* It is used as solvent for dyes, oils, perfumes, varnishes, gums, paints cosmetics etc.
* It is used as solid alcohol fuel. It is prepared by mixing ethanol with saturated
calcium acetate solution. A solid gel is formed is known as canned heat or solid
alcohol. It burn like alcohol.
* The commercial alcohol is made unfit for drinking by mixing in it some copper
sulphate ( to give color) and pyridine ( afoul smelling liquid). It is known as
denaturation of alcohol.
* It is used as antifreeze in automobile radiator, antiseptic, Petrol substitute (Power
alcohol).
* It is used in Thermometer, Spirit lamp, explosive etc.
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* Phenol are the aromatic hydroxy compounds in which one or more
hydroxyl (-OH) groups are directly attached to benzene ring. If –OH group is not directly
attached to benzene ring it is called aromatic alcohol.
* Simple phenol is hydroxy benzene or phenyl hydroxide or benzenol
or phenol itself also known as carbolic acid. It is represented as Ar-OH Or Ph-OH where
Ar or Ph is C6H5-group.
CLASSIFICATION OF PHENOL
Phenols are classified as mono, di and trihydric phenols according to the number
of hydroxyl groups attached to the aromatic ring.
1. Monohydric phenols
2.Dihydric phenols
3. Trihydric phenols
22 | P a g e
ELECTRONIC STRUCTURE OF PHENOL
* The O-H bond in phenol , like the O-H bond in alcohols, is formed by overlap of a sp3orbital of oxygen with 1s-orbital of hydrogen while the C-O bond is formed by the
overlap of a sp3-orbital of oxygen with a sp2-orbital of carbon of the benzene ring .
* The C-O-H bond angle in phenol is approx the same (1090) as in methanol but the
carbon-oxygen bond length in phenol is, however, slightly less (136pm) than methanol
(412pm).
* This is due to (i) resonance as a result of which carbon-oxygen bond acquires some
double bond character because of conjugation of the lone pair of electrons of oxygen with
the benzene ring and (ii) sp2-hybridised state of carbon to which oxygen in attached.
* Phenol has dipole moment 1.54D where as methanol has dipole moment 1.71D. This
smaller dipole moment of phenol is due to the electron attracting effect of phenyl group
in contrast to the electron releasing effect of methyl (or alkyl) group in alcohol
GENERAL METHODS OF PREPARATION OF PHENOLS
INDUSTRIAL METHOD
1. Middle oil fraction of coal tar distillation:
On reaction with aq. NaOH phenols are dissolved in it as phenoxide, CO2 is then blown
through this phenoxide ion solution to liberate phenols
Fractional
Coaltar
→ Middle oil (1700-2300)
Distillation
Excessive
→
washed
→
Middle oil fraction-basic
impurities (like pyridine)
H2SO4
aq NaOH
Middle oil fraction-Naphthalene separate
→
Cooling
CO2/H2O
C6H5ONa
→
Phenol-(crude) + Na2CO3
↓fractional distillation
Phenol-1800
Cresol-1900-2050
Xylols-2110-2350
On reaction with aq.NaOH phenols are dissolved in it as phenoxide, CO2 is then blown through
this phenoxide ion solution to liberate Phenols.
23 | P a g e
2. Hydrolysis of aryl halides (Dow’s process):
In this method, chlorobenzene is heated with excess of aqueous sodium hydroxide (6-8%)
at 623K under pressure of 320 atm. Sodium phenoxide formed in the process is
hydrolyzed.
using dilute hydrochloric acid to get phenol. Alternatively a current of carbon dioxide is
passed through aqueous sodium phenoxide to get phenol.
However if some electron withdrawing group is attached to benzene ring, then reaction
conditions get relaxed.
24 | P a g e
3. Oxidation of iso-propyl benzene (Cumene) :
Cumene (isopropylbenzene or 2-Propyl benzene or 2-Phenyl propene) is prepared
by friedel craft alkylation of benzene with propene or propyl chloride in presence of
phosphoric acid or AlCl3.This on aerial oxidation forms cumene hydroperoxide which
upon subsequent hydrolysis with an aq. acid gives phenol and propanone
This reaction is also called Auto-oxidation
4. From Chlorobenzene Rasching’s process:
When chlorobenzene is heated with steam at 500K in presence of Ca3(PO4)2 or SiO2 or
CuCl2 gives phenol. This method is more economical than Dow’s method since, HCl
produced can be reused in the preparation of Chlorobenzene from benzene. A mixture of
benzene vapours, air and hydrogen chloride is passed over heated CuCl2 at 500K.
25 | P a g e
LABORATORY METHOD
1. From benzene sulphonic acid:
Preparation of Phenol from benzene sulphonic acid involes three steps.
1) Step-I Neutralisation
Benzene sulphonic acid is neutralized by aq. alkali like NaOH. It forms sodium salt of
benzene sulphonic acid or sodium benzene sulphonate.
2) Step-II Fusion:
Sodium benzene sulphonate salt is fused with solid caustic soda at 573K to 623K. It gives
sodium phenoxide (sodium phenate) .
3) Step-III Acidification
Sodium phenoxide is then acidified with dil HCl/dil. H2O+CO2 mixture i.e. (Carbonic
acid) to get phenol.
The above reaction is laboratory method for preparation of phenol.
2. Hydrolysis of diazonium salt:
(I)
Benzene,on nitration gives Nitro benzene.
(II) On reduction of nitrobenzene in presence of Sn/HCl giveS Aniline.
(III) When Aniline is reacted with nitrous acid (NaNO2+HCl) at 273K to 278k gives
benzene diazonium chloride.
26 | P a g e
(IV) By acid hydrolysis to get Phenol.
3. Decarboxylation of salicylic acid:
Phenol is obtained by decarboxylation of sodium salt of salicyclic acid with soda lime
(CaO+NaOH) followed by acidification with dilute HCl.
4. Oxidation of Grignard reagent:
When oxygen is bubbled through an ethereal solution of phenyl magnesium bromide it
forms an addition product which upon treatment with a dilute mineral acid gives phenol.
27 | P a g e
5. Oxidation of aromatic hydrocarbons:
On Oxidation ,Toluene gives phenol in presence of cupric salt as a acatalyst.
PHYSICAL PROPERTIES OF PHENOL
1.Physical state
*At ordinary temp. lower alcohols are colourless liquids with distinct smell and burning
taste. The higher members are colourless, odourless waxy solids. but they reddish
brown due to auto oxidation on exposure to air and light. 
*Phenols are poisonous in nature but act as disinfectant and antiseptic. 
2.Solubility
*Phenols form H-Bonds with water molecule and hence soluble in water, but their
solubility is lower than that of alcohols because of large hydrocarbon part .Phenols, like
alcohols,also form intermolecular hydrogen bonds
*Phenols, like alcohols, exist as associated molecules.
3.Boiling point
*Phenols have much higher boiling point than there corresponding
hydrocarbons due to intermolecular hydrogen bonding.
*Amongst the isomeric nitrophenols, o-nitrophenol is steam volatile due to
chelation (intramolecular H-bonding) while p-isomer is not steam volatile due to
association of molecules by intermolecular H-bonding. Further, due to chelation,
o-nitrophenol has lower m.p. and b.p. lower acidity and lower solubility in water
than p-nitrophenol.
28 | P a g e
On the other hand meta and para nitrophenol exhibit intermolecular H-bonding with their
own molecules as well as with water molecules and hence show comparatively higher
melting and solubility.
(i) Intermolecular H-bonding (m –nitrophenol)
(ii) H- bonding with water molecules ( m-nitrophenol)
(iii) Intermolecular H- bonding ( p –nitrophenol)
(iv) H – bonding with water molecules ( p – nitrophenol)
CHEMCIAL PROPERTIES OF PHENOL
(A)Reactions involving cleavage of O- H bond
1. Acidic character of phenol
(i) Reaction with active metals:
Phenols are weak acidic in nature. they can react with active alkali metals (NaOH, KOH)
to form salts known as phenoxides or phenates.
29 | P a g e
(ii)Reaction with alkalies
*They do not react with carbonates and bicarbonates. Phenols are weaker acid as
compared to carboxylic acid because of polar O-H group in them. The acidic nature
of phenol is due to formation of stable phenoxide ion in solution to give H+.
Comparison of acidic character of alcohols and water
Alohol behave as Bronsted acids, i.e. they can donate a proton to a strong base (:B ).
..
-..
-
B:
+ H-O-R
..
Base
Alcohol(acid)
→ B-H
+
(conjugated acid)
: O-R
..
Alkoxide ion(conjugated base)
However, when an alkoxide ion reacts with water, the starting alcohol is obtained.
..
..
..
-..
R-O:
+
H-O-H
→
H-O-R
+
:OH
..
..
..
..
-
Base
Acid
(conjugated acid)
(conjugated base)
This reaction suggests that water is a better proton - donar than alcohol. alcohols are
weaker acids than water. Conversely, alkoxide ion is a better proton acceptor than
hydroxide ion.i.e. alkoxides are stronger bases than hydroxide ion.
Explanation for stronger acidic character of phenols than alcohols
*phenols are stronger acid than alcohols
i.)The greater acidity of phenol is due to stability of phenoxide ion is resonance
stabilized.
ii.) Resonance structure of phenol
30 | P a g e
iii.) As a result of resonance, the oxygen atom acquires a partial charge. this weakens the
O-H bond and thus facilities the release of a proton. thus, facilities the release of a proton.
Thus, phenols like alcohols also act as Bronsted acids facilitates the release of proton
(H+) to give phenoxide ion which is also stable due to resonance
iv.) Resonating structure of phenoxide ion .
v.) Both phenol and phenoxide ion are stabilized by resonance. But phenoxide ion is
more stabilized than phenol because the resonating structure of phenoxide ion carry
only negative charge of phenol involves separation of positive and negative charge.
Hence, phenol has a strong tendency to form more stable phenoxide ion by releasing
a proton.In contrast, neither the alcohol nor the alkoxide ion is stabilized by
resonance.
Effect of substituent on the acidity of phenols
a.Electron withdrawing group (EWG)
*Electron withdrawing groups NO2 , -X, -CHO, -COOH, -CN etc. stabilizes the
phenoxide ion more by dispersing the negative charge relative to phenols ( i.e. proton
release become easy) and thus increases the acidic strength of phenols
Particular effect is more when the substituent is present on o– and p-positions than
in m- position. Thus acidic strength of nitrophenol decreases in the order
p-nitrophenol > o-nitrophenol > m-nitrophenol > phenol
*Further greater the number of electron withdrawing groups at o- and p – position,
more acidic the phenol.
b.Electron donating group (EDG)
(i) Electron donating group –R, -NH2, -OR etc destabilize the phenoxide ion by donating
electrons and intensify the negative charge relative to phenol (i.e. proton release become
difficult)and thus decreases the acidic strength of phenol.
31 | P a g e
(ii)The effect is more when the substituent is present on o- and p-position than on mposition with respect to –OH group. Thus cresol are less acidic than phenol.
m – methoxy and m-amnion phenols are stronger acid than phenols because of –I
effect ( of –OCH3 and –NH2 groups) and absence of +R effect.
m –methoxy phenol > m-amino phenol > phenol > O-methoxy phenol > p-methoxy phenol
2.Ester formation :
Phenols also react with acid chloride and anhydrides to give esters in excellent
yields.
The reaction with acetyl chloride is usually catalysed by a base such as pyridine, that
with acetic anhydride is catalysed both by acids (a few drops of conc. H2SO4) and bases
(sodium acetate, pyridine).
Reaction with benzoyl chloride is known as benzoylation
Benzoylation of alcohols o phenols in presence of NaOH is called SchottenBaumann reaction
32 | P a g e
3.Ether formation:
Phenol react with alkyl halide in presence of NaOH give alkoxy benzene.
NaOH
C6H5OH
+
CH3CH2Br
→ C6H5OCH3CH2 +
Ethoxy benzene
NaBr
+
H2 O



4.Claisen Rearrangment of Aryl Allyl Ethers
Reaction type : Electrocyclic reaction or sigmatropic rearrangement
*Aryl allyl ethers undergo a thermal rearrangement to give ortho-allyl phenols.
*This reaction is an intramolecular process.
*A sigmatropic rearangement is a reaction is which a σ bond migrates from one end of a
π system to the other.
(B) Electrophilic aromatic substitution reaction
The hydroxyl group is a powerful activating group and hence phenols readily undergo
electrophilic substitution reactions. In this reaction, an electrophile (electron loving species)
attacks the benzene ring and replaces one of its hydrogen atoms. Since the ortho and
para positions of the phenol are electron rich, the substitution takes place at these positions.
Two such reactions are halogenation and nitration reactions. Let us now study them in
details.
33 | P a g e
1. Halogenation
Phenol reacts with bromine in aqueous solution to give 2, 4,6- tribromophenol in
about 100% yield. Bromination can be limited to mono bromination to give mainly 4bromophenol using low temperature and less polar solvent such as carbon disulphide. The
other product formed in minor quantity is 2-bromophenol.
Due to steric hinderance at ortho position, para-product predominates
2. Sulphonation :
34 | P a g e
3. Nitration:
Phenol gives a mixture of 2-nitro and 4-nitrophenols on nitration with dilute nitric acid.The
mixture of nitrophenols so obtained is separated using steam distillation. Both these
products show hydrogen bonding. In case of 2-nitrophenol, the hydrogen bonding is
intramolecular (in the same molecule) whereas in case of 4-nitrophenol, it is
intermolecular (between different molecules). Nitrophenol is steam volatile and distills
out on passing steam whereas 4-nitrophenol is less volatile due to intermolecular hydrogen
bonding.
Treatment of phenol with a mixture of conc. nitric acid and conc. sulphuric acid at 323K
yields 2,4,6-trinitrophenol also known as picric acid.
4. Mercuration
35 | P a g e
4. Friedel crafts alkylation and acylation Phenol reacts with alkyl halides in presence of
anhydrous AlCl3 to form para product with a small quantity of ortho isomers
6.Nitrosation
Phenol is treated with Nitrous acid (NaNO2+HCl) and nitrosophenol thus obtained
is oxidized with dil. HNO3, the yield of mononitrophenol is increased.
36 | P a g e
7. Kolbe’s reaction:
involves sodium phenoxide which is allowed to absorb carbon dioxide and then
heated under a pressure of CO to 398 K. Sodium salicylate so obtained on
acidification yields
Mechanism
37 | P a g e
Acetyl salicylic acid ( Aspirin) (2-acetoxy benzoic acid)
Salicylic acid is the starting material for the manufacture of 2-acetoxybenzoic acid
.It is obtained by acetylating salicylic acid with acetic anhydride (Sodiumacetate or
acetic acid) and few drops of conc.H2SO4.
It is a white solid (m.pt. 408K) and is used for relieving pain (analgesic) and to bring
down the body temperature (antipyretic during fever)
(b) Methyl salicylate
It is prepared by refluxing salicylic acid with methyl alcohol
*It is an oily liquid (b.pt. 495K) with pleasant odour (oil of wintergreen) used in
perfumery and flavorings agent.
*It is also used in medicine in the treatment of rheumatic pain and as a remedy
for aches, sprains and bruises.
38 | P a g e
(c) Phenyl salicylate ( salol)
It may be prepared by heating salicylic acid with phenol in the presence of
phosphoryl chloride.
It is white solid (m.pt 316K) and is used as an intestinal antispeptic.
8. Reimer-Tiemann reaction:
When phenol is refluxed with chloroform in the presence of aqueous sodium
hydroxide at 340K followed by hydrolysis,an aldehyde group (-CHO) gets
introduced in the ring at apposition ortho to the phenolic group. Ortho hydroxyl
benzaldehyde or Salicyldehyde is formed as the product of the reaction.
This reaction is called Reimer-Tiemann reaction.In addition to O-salicyldehyde,
small amount of p-salicyldehyde is also formed but the major product is ortho.
Mechanism
The electrophile, dichloromethylene CCl2 is generated from chloroform by
action of base
OH- + CHCl3 ⇆ HOH + CCl3 → Cl- +:CCl2
39 | P a g e
Attack of electrophile ( :CCl2) on phenoxide ion
Salicylaldehyde
If the reaction is carried out with carbon tetrachloride (CCl4) instead of
chloroform, o -hydroxy benzoic acid (salicylic acid) is formed.
TESTS TO DISTINGUISH BETWEEN ALCOHOLS AND PHENOLS
1. Litmus test
Phenol turns blue litmus red being acidic in nature but alcohol do not.
They turn blue litmus paper red. Acidity of phenol is due to the formation of H+ ion
and stable phenoxide ion in the solution.
C6H5OH + 2Na → 2C6H5ONa + H2↑
C6H5OH + NaOH → C6H5ONa + H2O
2. Ferric chloride test
Phenol react with neutral ferric chloride solution to form violet or green
colored solution (water soluble complex compounds) where as alcohol
do not undergo such reactions.
40 | P a g e
3C6H5OH + FeCl3 → (C6H5O)3Fe + 3HCl
(C6H5O)3 Fe : Ferric phenoxide ( violet complex)
In fact, all compound containing enolic group (=C-OH) give this test.
3. Bromine water test
Aqueous solution of phenol forms white precipitate of 2,4,6-tribromo phenol,
when treated with bromine water. However alcohol so not give such
precipitation.
USES
* Dilute solution of Phenol is used as antiseptic and disinfectant.
* Phenol is used in preparation of salicylic acid, Aspirin (analgesic), phenacetin ,
paracetamol (antipyretics) and dyes (Phenolphthalein)
* Phenol is used in preparation of explosive such as picric acid.
* It is used as preservative for wood and ink.
* It is used to prepare 2, 4- dinitro phenoxy ethanoic acid which is selective weed
killer.
* It is used in preparation of adhesive i.e. Bakelite resin (phenol formaldehyde
resin), epoxy resin, ion exchange resin.
41 | P a g e
Ethers are organic compounds containing divalent oxygen atom attached to two
same or different alkyl groups. In ether divalent oxygen atom (-O-) is a
functional group.
Ethers have a general formula R - O - R’, where R and R’ may be same or
different alkyl or aryl or arylalkyl groups.

*Ethers can be classified as follows:
(I)Aliphatic ethers
If both R and R’ groups are alkyl groups, then ether is aliphatic ether
CH3 – O – CH2CH3 (ethyl methyl ether)
CH3CH2 – O – CH2CH3 (diethyl ether)
(II)Aromatic ether
If both R and R’ or any of them is aryl group then ether is aromatic ether
CH3– O –C6H5 ( methyl phenyl ether)
C6H5 – O – C6H5 (Diphenyl ether)
Depending upon the nature of alkyl group s attached to oxygen, ethers are two types
(III)Simple or symmetrical ether
If two group R and R’ present in ether are same, then it is known as simple or
symmetric ether
CH3 – O – CH3 (Dimethyl ether)
C2H5 – O – C2H5 (Diethyl ether)
C6H5 – O – C6H5 (Diphenyl ether)
(IV)Mixed or unsymmetrical ether
If R and R’ present in ether are different, then ether is known as mixed or
unsymmetrical ether
CH3 –O – C2H5 (ethyl methyl ether)
CH3–O-C6H5 (methyl phenyl ether)
C6H5 – O – CH2C6H5 (Benzyl phenyl ether)
Isomerism in Ethers
1.Functional Isomerism:
both –O- and –OH are the functional groups.
42 | P a g e
Ethers are isomeric with mono-hydric alcohol eg.-C2H6O
CH3CH2OH ( ethyl alcohol)
CH3 – O –CH3 ( dimethyl ether)
2.Metamerism:
Ethers containing more than three carban atoms shows such type of isomerism.
CH3-CH2-CH2-O-CH3
Methyl n-propyl ether
C2H5-O-C2H5
Diethyl Ether
3.Chain isomerism
It is due to difference in the nature of carbon chain.
CH3-O-CH2-CH2-CH2-CH3 CH3-O-CH2-CH-CH3
n-butyl methyl ether
CH3
Isobutyl methyl ether
STRUCTURE
Ether may be considered as dialkyl derivative of water. In ether , oxygen atom
undergoes sp3 hybridization.It has structure similar to that of water. oxygen atom has
four sp3 hybrid orbitals out of four, two sp3 hybrid orbitals form two sigma bond with
two alkyl groups by sp3-sp3 overlapping. Remaining two sp3 hybrid orbitals contains
lone pair of electrons. It has bent or angular structure C-O-C bond angle in ether is
1100 which is greater than water, This is because in ethers alkyl groups have repulsive
forces among themselves but in water. This repulsion between the H-atom is absent.
thus ether possess net dipole moment.
ETHERS
43 | P a g e
GENERAL METHOD OF PREPARATION OF ETHERS
1. Dehydration of alcohols
(i) Acidic dehydration of alcohols
This method is used to prepare simple or symmetrical ether. In this reaction, reaction
conditions have to be carefully controlled, to get the maximum yield of ether. At a
slightly higher temperature (150oC) alkene is obtained instead of ether.
Mechanism
SN1 mechanism
SN2 mechanism
Primary alcohols reacts by generally SN2 mechanism where as secondary and tertiary
alcohols undergo the reaction by SN1 mechanism
Order of ease of dehydration of alcohol to form ethers
1O alcohol > 2O alcohol >3O alcohol
(ii)Catalytic dehydration
(Al2O39523K)
2R-OH
→
R-O-R + H2O
44 | P a g e
2.Williamson synthesis
When Sodium alkoxide is heated with alkyl halide in alcohol, ethers are obtained . This
method is called Williamsons synthesis. It is laboratory preparation method of ethers.
R’ – ONa + X – R → R’ – O – R + NaX
Both symmetric and unsymmetrical ethers can be prepared by this method Mechanism
Symmetric or simple ether
C2H5ONa ⇌ C2H5O- + Na+
Unsymmetric or Mixed ether
CH3-O-Na + Br-C2H5 → CH3-O-C2H5 + NaBr
Order of reactivity of alkyl halides towards this reaction is
Primary > secondary > tertiary
For better yield, the alkyl halide should be primary and alkoxide should be
secondary or tertiary
3. Action of silver oxide on alkyl halide
heat
2RX + Ag2O → R-O-R + 2Ag
4. Action of diazomethane on alcohols
When Diazomethane is reacted with alcohol in presence of fluoroboric acid or BF3 it gives
methyl ethers.
HBF4
CH3-CH2-OH + CH2N2
→
Diazomethane
CH3-CH2-OCH3 + N2
ethyl methyl ether
(mixed ether)
5. Reaction of lower halogenated ether with Grignard reagent
45 | P a g e
6. Addition of alcohols to alkene
By direct addition of alcohols to reactive alkenes in presence of acids as catalyst.
Mechanism
H2SO4 → H+ + H2SO4-
PHYSICAL PROPERTIES OF ETHERS
* dimethyl ether and ethyl ether are gases while All ethers are colourless liquids at
room temperature
* Ethers are sparingly soluble in water but readily soluble in organic solvent like alcohol,
chloroform, Benzene etc.
*The solubility of lower ethers in water is due to formation of hydrogen bonding with
water but tendency to form hydrogen bonding decrease in number of alkyl groups.
Hence ethers are not soluble in water.
* Ethers are lighter than water and they form upper layer when mixed with it.
* they are highly inflammable.
* When ethers are exposed to oxygen in presence of sunlight they form explosive
hydroperoxide.
* Due to the low polarity of ethers they do not form inter molecular hydrogen bonding
therefore they have low boiling points than isomeric alcohols and almost same as
alkanes of comparable molecular weight.
* Ethers are polar in nature and its dipole moment ranges from 1.15D to 1.30D
46 | P a g e
CHEMICAL PROPERTIES OF ETHERS
Ethers are relatively, almost as inert compound, These are not easily attacked by alkalies,
dilute mineral acid. they are stable to catalytic hydrogenation and to other reducing
agents such as LiAlH4. this is due to the reason that the functional group of ethers(-O)
does not contain any active site in their molecules as compared to hydroxyl (-OH) group
of alcohols and phenols even though the oxygen atom atom in both these functional
groups contains two lone pairs of electrons. However, under specific conditions, ethers
undergo the following reactions.
(I)Reactions of the ethereal Oxygen
1. Action of concentrated acids(formation of oxonium salt)
The oxygen atom in ether molecule has two lone pairs of electrons, Therefore, ethers
actas Lewis bases and dissolve in cold concentrated mineral acids(H2SO4,HCl) to form
stable oxonium salts.
+
R-O-R+H2SO4(Cold) →(R- O: - R) HSO4H
Dialkyl Oxonium hydrogen sulphate
2.Reaction with Lewis acids:
Being Lewis bases, ethers form complexes with lewis acids such as BF3, AlCl3,
FeCl3,etc.these complexes are called etherates.
CH3 CH2
CH3 CH2
..
..
O + BF3
→
CH3 CH2
CH3CH2
O
..
BF3
Boron trifluride etherate (complex)
(II) Reaction involving the cleavage of carban – oxygen bond
1. With halogen acids:
Ethers are cleaved by strong acids HI or HBr, but HCl does not cleave ethers.This is
because, HI or HBr are sufficiently acidic to protonate ethers while iodide and bromide
ions are good nucleophiles for substitution Ethers are heated with excess of concentrated
hydrogen halide to give alkyl halides. The order of reactivity of hydrogen halides is
Reactivity of halogen acid
HI > HBr > HCl
Mechanism
47 | P a g e
[During the cleavage of unsymmetrical ethers, smaller alkyl group produces alkyl halides]
(A) In cold a simple ether gives one molecule of alkyl halide and one molecule of an
alcohol, while when heated gives two molecules of alkyl halide.
Cold
→ R-X + R-OH
∆
R-O-R + HX → R-X + H2O
(B)In cold a mixed ether gives generally a lower alkyl iodide and a higher alcohol while when
heated it gives two different alkyl halides.
R-O-R + HX
Cold
R-O-R’ + HX →
R-O-R + HX
R-X
∆
→
+
Lower
R’-OH
Higher
R-X + R’-X + H2O
2. With sulphuric acid:
On heating with dil. H2SO4under pressure, ethers are hydrolysed to alcohols.
R-O-R + H2O
Dil.H2SO4. ∆
→
2R-OH
Under pressure
3. With phosphorus pentachloride:
Phosphorus pentachloride also bringsabout the cleavage of carbon-oxygen bond of ethers
leading to the formation of alkyl halides.
∆
R-O-R + PCl5 → 2R-Cl + POCl3
Alkyl chloride
4. Reaction with acid chlorides and anhydrides:
Acid chlorides react with ethers when heated in the presence of anhydrous ZnCl2 or AlCl3
to form alkyl halides and esters.
Anhydrous ZnCl2
C2H5-O-C2H5 + CH3COCl
→
C2H5Cl + CH3COOC2H5
48 | P a g e
(III) Reaction involving the alkyl group
1. Action of air(Formation of peroxides)
On exposure to sunlight, ethers slowly react with oxygen from air to form hydroperoxides
or peroxides which are explosive
CH3-CH2-O-CH2-CH3 + O2→ CH3-CH-O-CH2-CH3
O-O-H
1-Ethoxy ethyl hydroperoxide
2. Halogenation :
Ethers react with chlorine or bromine in the dark to give substituted products. The extent
of substitution depends upon the reaction conditions. for example, diethyl ether react with
chlorine in the dark to give α,α-dichlorodiethylether in which the halogenation
preferentially occurs at α-carbon atoms.
(IV) Electrophilic substitution reaction
The alkoxy group (-OR) is ortho, para directing and activates the aromatic ring towards
electrophilic substitution in the same way as in phenol
(i)Halogenations:
Phenylalkyl ethers undergo usual halogenation in the benzene ring, e.g., anisole
undergoes bromination with bromine in ethanoic acid even in the absence of iron (III)
bromide catalyst. It is due to the activation of benzene ring by the methoxy group. Para
isomer is obtained in 90% yield
49 | P a g e
(ii) Nitration:
Anisole reacts with a mixture of concentrated sulphuric and nitric acids to yield a mixture of
ortho and para nitroanisole.
(iii) Friedel crafts reaction :
Anisole undergoes Friedel-Crafts reaction, i.e., the alkyl and acyl groups are introduced at
ortho and para positions by reaction with alkyl halide and acyl halide in the presence of
anhydrous aluminium chloride (a Lewis acid) as catalyst
Alkylation
Acetylation
USES OF ETHER
1.It act as an industrial solvent for oils, resins, gums, etc.
2.Ethoxyethane has been used as an inhalation anaesthetic agent in surgery. however,
because of its slow effect and unpleasant recovery period, other compound such as
ethrane (or enflurane) and isoflurane (or forane) and penthrane (methoxyflurane) have
replaced ethoxyethane as an anaesthetic agent.
3.It is used as refrigerant for cooling.
4.A mixture of diethyl ether and ethyl alcohol, known as Natalite, is used as fuel.