ALCOHOL

INTRODUCTION:
Alcohols are organic compounds in which one or more hydrogen atoms from hydrocarbon have
been replaced by hydroxyl (-OH) group. They are some of the most common and useful
compounds in nature, in industry, and around the house. The general formula for a simple acyclic
alcohol is CnH2n+1OH, where n=1, 2, 3, etc. The saturated carbon chain is often designated by the
symbol R, so that ROH can represent any alcohol in the homologous series. Alcohols can be
viewed as organic analogues of water in which one hydrogen atom is replaced by an alkyl group.
The simplest and most commonly used alcohols are methanol and ethanol. They occur widely in
nature and have many industrial and pharmaceutical applications.

CH3OH CH3 CH2 OH

Methanol Ethanol

Aromatic compounds, which contain a hydroxy group on a side chain, behave like alcohols are
3
called aromatic alcohol. In these alcohols, the —OH group is attached to a sp hybridised carbon
atom next to an aromatic ring.

CH2OH CH CH OH CH CH CH OH
2 2 2 2 2

benzyl alcohol 2 - phenyl ethanol 3 - phenyl propanol

3
In some alcohols, the -OH group is attached to a sp hybridised carbon next to the carbon-
carbon double bond that is to an allylic carbon are known as allylic alcohols. In some alcohols
—OH group bonded to a carbon-carbon d ouble bond i.e., to a vinylic carbon or to an aryl
carbon. These alcohols are also known as vinylic alcohols. Allylic and benzylic alcohols may be
primary, secondary or tertiary in nature.

OH
CH2 CH OH CH2 CH CH2 OH
vinylic alcohol allylic alcohol
phenol
CLASSIFICATION OF ALCOHOLS: Alcohols are classified into following types on
the basis of number of –OH groups present in the molecule and nature of carbon attached with –OH
group as follow:

(a) Monohydric Alcohols: These compounds contain only one –OH group.

CH3CH2OH CH3CH2CH2OH

(b) Dihydric Alcohols: These contain two –OH groups.

 CH2 OH
CH2 OH

(c) Trihydric Alcohols: These contain three –OH groups.

CH2 OH
CH OH
CH2 OH

On the basis of nature of carbon atom attached with -OH group the mnohydric
Alcohols can be further classified as primary (1°), secondary (2°), or tertiary (3°)
depending on the number of carbon atoms bound to the hydroxyl-bearing carbon.

(a) Primary alcohol (1° alcohol): A primary alcohol has one alkyl group attached to
the carbon bound to the –OH, i.e., a compound in which the hydroxyl group is
bounded to a primary carbon. Primary alcohols have the group –CH 2OH, where
the carbon atom with the alcoholic hydroxyl group has at least two additional
hydrogen attached to that carbon. Primary alcohol has –OH gr oup bonded to a
carbon which is bonded to one other carbon:

H H

H C C OH

H H

(b) Secondary alcohol (2° alcohol): A secondary alcohol has two alkyl group attached
to the carbon bound to the –OH, i.e., the hydroxyl group is bounded to a secondary
carbon. Secondary alcohols have the group –CHOH, where the carbon atom with the
alcoholic hydroxyl group has only one additional H atom attached to it. There are two
R groups (R stands for any other organic chain or group), and the alcoholic hydroxyl
group is attached to a secondary carbon. Secondary alcohol has –OH group bonded to
a carbon which is bonded to two other carbon:

H OH H

HC C C H

H H H

(c) Tertiary alcohol (3° alcohol): A tertiary alcohol has three alkyl group attached to
the carbon bound to the –OH, i.e., the hydroxyl gro up is bounded to a tertiary carbon.
 Tertiary alcohols have the group –COH, wher e the carbon atom with the alcoholic
hydroxyl group has no additional H atoms attached to it.

H CH3 H

H C C C H
H OH H
If we replace hydrogen with a –OH group we get the following groups for three
alcohols:

CH2OH CH OH C OH

primary alcohol secondary alcohol tertiary alcohol

OH
OH OH
OH C CH3
CH3 CH2 CH CH3 CH3 CH2
primary alcohol CH3
secondary alcohol secondary alcohol tertiary alcohol

NOMENCLATURE OF ALCOHOLS

According to the IUPAC system of nomenclature, alcohols are called alkanols.

They are named as the derivatives of the corresponding alkane in which the -e of the
alkane is replaced by -ol. The IUPAC have come up with a set of rules that are used to
name any alcohol regardless of its complexity. These rules are summarized as follows:

Step 1. Name the longest continuous chain to which the hydroxyl (—OH) group is
attached. Count the number of carbon atoms and identify the corresponding alkane.
The name for this chain is obtained by dropping the final -e from the name of the
hydrocarbon parent name and adding the ending -ol.

Step 2. Number the longest chain to give the lowest possible number to the carbon
bearing the hydroxyl group.

Step 3. Locate the position of the hydroxyl group by the number of the carbon to which
it is attached.

Step 4. Number the any other substituents according to their position on the chain.
Step 5. Combine the name and location for other groups, the hydroxyl group location,
and the longest chain into the final name.
 Step 6. If there are more than one –OH group do not remove the –e from the suffix,
but add a di- or tri- prefix to the –ol suffix.

Step 7. Identify and locate the other branches on the chain so that they are named
alphabetically and their carbon number is hyphenated onto the front of the name.

viz; Alcohols Common name IUPAC name

CH3OH Methyl alcohol Methanol

CH3CH2OH Ethyl alcohol Ethanol

CH3CH2 CH2OH n-Propyl alcohol 1-Propanol

CH3CHOHCH3 Isopropyl alcohol 2-Propanol

CH3(CH2)2CH2OH n-Butyl alcohol 1-Butanol

CH3(CH2)3CH2OH n-Pentyl alcohol 1-Pentanol

Other examples:

OH CH3 OH
CH3 CH CH2 CH3 CH3 CH CH2 CH2 CH CH3
OH
2 5 2
- butanol methyl hexanol cyclopentanol

OH OH OH OH
CH2 CH 2
CH2 CH CH3
1 2 3 OH CH3 CH
, , - 3 1
NH2
1 2 3 trihydroxy propane 3- -1- 3
cyclopentyl propanol --amino 2- butanol
OH
OH

CH2 CH CH OH CH3

CH3
3 2 CH3 CH3
- butene - - ol .
3 - meyhylcyclohexanol 2 3 - dimethylcyclooctanol
METHOD OF PREPARATION OF ALCOHOLS

The following methods are used for the preparation of alcohols:

1. Hydrolysis of haloalkanes: Haloalkanes can be converted to corresponding alcohols

using aqueous NaOH, KOH or Ca (OH)2. With this method primary and
secondary alcohols are formed from a primary and secondary halogenoalkanes.
This is a type of nucleophilic substitution reaction (S N). This reaction is useful
only with reactants that do not undergo E2 elimination readily.

H2O

RX+OH ROH + X
H2O
CH3CH2CH2Br + NaOH(aq) CH3CH2CH2OH + NaCl

2. Reduction of carbonyl compounds: Carbonyl compounds (which contain –C–O group)

such as aldehydes, ketones, carboxylic acids and esters can be reduced to alcohols.
Aldehydes give primary alcohols while ketones yield secondary alcohols, either by
catalytic hydrogenation or by use of chemical reducing agents like lithium aluminum
hydride, LiAlH4. Carboxylic acids and esters also give primary alcohols on reduction
with hydride reagents such as LiAIH4 and sodium borohydride
(NaBH4). NaBH4 does not reduce carbon-carbon double bonds, not even those conjugated with
carbonyl groups, and in thus useful for the reduction of such unsaturated carbonyl compounds to
unsaturated alcohols. In the above reactions it is observed that only the carbonyl group is reduced and
the other functional groups remain unaffected. Highly selective behaviour of NaBH4 makes the
preferred reagent for the reduction of carbonyl groups in sensitive poly functional group containing
compounds.

+ –
3. From hydration of alkenes: Hydration i.e.s addition of H and OH across a C=C
double bond to give alc ohols. This is an electrophilic addition of H2O to the alkene.
Alcohols can be prepa red by adding water to an alkene in the presen ce of a strong
acid such as co. H2SOO4. Because these reactions follow Markovnikov's rule, the
º º
product of the reaction is often a highly substituted 2 or 3 alcohol.

RCH=CH2 + H2SO 4 →RCH-CH3 RCHOHCH3

CH2=CH2 + H2SO4 →CH3-CH2HSO4 CH3CH2OH

Ease of preparation is tert. > sec. > prim alcohol; ease of dehydr ation follows
same sequence.

4. Oxidation of organoboranes: When an alkene reacts with BH3 (a boron hydride)

in THF solution, an org anoborane is obtained. Hydroboration followed by oxidation
will produce an alcoho l. Since BH3 has three hydrogens, above addition can occur
three times to give tria lkylborane. This is oxidised to alcohol by hydr ogen peroxide
(H2O2) in the presence of aqueous sodium hydroxide. The overall reaction is addition
of water across the double bond opposite to that of Markovni kov’s rule and the
reaction is regiosele ctive producing the least substituted alcohol.
Except ethyl alcohol no other primary alcohol can be obtained by this met hod,
however hydroboration of terminal alkenes give primary alcohols.

5. From Grignard reageents – Alcohol can easily be prepared by using Grignard

(RMgX) reagent as folloow:

(a) By reaction with aldehydes & ketones: The reaction of Grignard reagents with
formaldehyde produces a primary alcohol, with other aldehydes, secon dary alcohols
and with ketones, tertiary alcohols. In this method alcohol is prepa red with the
formation of new carbon-carbon bonds.

0
All other aldehydes yield 2 alcohols on reaction with Grignard reagents.
OH
CH3 i ether
CH CH MgBr CH3CH2 CHCH3
+
32 C O ii H O
H 3

CH3 H CH3
CH3 CH C O
+
CH3MgI H+ CH3 CH CH OH

0
With ketones, Grignard rea gents give 3 alcohols. CH3

CH3
CH3 i ether
C OH
CH3CH2MgBr C O + CH3CH2
ii H3O
CH3 CH3

(b) By reaction with esters: Produces tertiary alcohols in which two of the
substituents on the hydroxyyl- bearing carbon are derived from the Grignardd reagent.
 O
MgBr
C OCH2CH3
NH +
4 C OH

(c) By reaction with epoxxides: Grignard reagents react with epoxide to yield primary
alcohols containing two or more carbon atoms.

5. Fermentation: Ethanol is prepared on a large scale using fermentation process. It

involves breaking down large molecules into simpler ones using enzymes.
Usually, yeast is added as a source of enzymes. Yeast converts the reactant glucose
or fructose into ethanol and carbon dioxide in presence of zymase enzyme.

ACIDIC NATURE OF ALCOHOLS:

Alcohols can act as Brönsted acids as well as Lewi s base due to donation of proton and presence of
unpaired electron on oxygen respectively. Alcohols are very weak acids because the alkyl group
pushes electrons towards the —OH group, so that the oxygen does not strongly attract the electrons
-
in the —OH bond. Furthermore once a RO ion is formed, it cannot be stabilized by the
delocalization of the charge. Thus alcohols react only to a very slight extent with alkali, but will react
with very electropositive metals under anhydrous conditions to give alkoxide with the general
- +
formula RO M .
Example: Reaction of ethanol with sodium
- +
2CH3CH2OH + 2Na 2CH3CH2O Na + H2

Addition of water will regenerate the alcohol readily.

- +
CH3CH2O Na + H2O CH3CH2OH + NaOH

The reaction is much slower than the reaction of water with sodium. Alcohols tend to
be slightly less acidic (pKa = 15) compared to water (pKa = 14). The higher the pKa
value the lower is the acid strength. The reaction of alcohol with sodium can be used
to deposite the excess sodium in the laboratory. Even alcohols are neutral to litmus
and do not reacts with alkali like NaOH but contain active hydrogen atom so reacts
with Na or K metal.

CH3CH2OH + NaOH No reaction

Reactivity of alcohol towards metal: 1° > 2° > 3° alc ohol. An electron-releasing

group (-CH3, -C2H5) increases electron density on oxygen tend to decrease the
polarity of O-H bond. For example, with methanol:

++ NaOH H2SO4 +
H CH3 ONa CH3 OH CH3 OH2
Sod. Strong Methanol Strong Protonated
methoxide base acid methanol

(i) The lower alcohols are colourless liquids with a characteristic smell and a burning
taste. The higher members (with more than 12 carbons) are colourless wax like solids.

(ii) Because of hydrogen bonding, alcohols tend to have higher boiling points than
comparable hydrocarbons and ethers of similar molecular weight. Alcohols exists
associated molecules due to the association of molecules in the liquid phase through
strong intermolecular hydrogen bond between hydrogen atom of one molecule and
oxygen atom of another molecule. The oxygen-hydrogen bond is polar because
oxygen is much more electronegative than hydrogen. The lowers members have low
boiling points. With the increase in molecular weight, the boiling points keep on
increasing gradually. For example, the boiling point of butyl alcohol is 118°C whereas
the boiling point of the isomeric diethyl ether is 36°C.

(iii) Solubility: The general rule in solubility is “like dissolves like.” The hydroxyl group
generally makes the alcohol molecule polar and therefore more likely to be soluble in
water. Hydrogen bonding also has an effect on water solubility. The OH groups of an
alcohol can hydrogen bond with water, and so this portion of the alcohol is hydrophilic.
On the other hand, the alkyl chain in an alcohol is similar to hydrophobic molecules like
hydrocarbon that do not mix with water. Compounds like alcohols that have hydrophilic
and hydrophobic regions are called ambiphilic (or amphiphilic). The water solubility of a
given alcohol depends on whether the hydrophilic OH or the
hydrophobic alkyl chain dominates. Alcohols with shorter carbon chains
(CH3OH,CH3CH2OH, CH3CH2CH2OH) are usually more soluble than those with longer
carbon chains because the increasing size of the nonpolar chain disrupts the hydrogen
bonding network. Formation of hydrogen bonds with water will increase their solubility.
That is why alcohols are much more soluble in water than their corresponding alkanes,
aromatic hydrocarbons, alkyl halides or aryl halides. Amongst isomeric alcohols, the
solubility increases with branching.

(iv)The B.P. and M.P. will also increase with carbon chain length. The longer the
alcohols carbon chain, the better the chance that the alcohol will be a solid at room
temperature. Alcohols show higher boiling points than alkane and ethers of similar
mass due to hydrogen bonding. Since there is not any possibility of hydrogen bonding
in ether, the forces between the ether molecules are much weaker and can be much
more easily vaporized.
CH3CH2CH2CH2CH2CH2CH2CH2OH
CH3CH2OH
Insoluble in water
Soluble in water O
H H
O
O
H H
H3C H
R R
R O
..... O H
O H ..... OH H
H

Comparison of boiling points among isomeric alcohols

CH3 CH3
CH3CH2CH2CH2OH CH3 CH CH2OH CH3 C OH
CH3
1_ _ 1_ 2_ 2_
butanol 2 methyl propanol methyl propanol
0 0 0
B.P. 118 C B.P. 108 C B.P. 83 C
74 74 74
M.Wt = M.Wt = M.Wt =

(v) The viscosity of small alcohols is much higher than the viscosity of alkanes.

(vi) Generally alcohols are lighter than water, i.e., less dense than water. Density of
alcohols increases with molecular mass.
CHEMICAL REACTIONS OF ALCOHOLS:
Alcohols acts both as nucleophiles as well as electrophiles. The bond between O-H is
broken when alcohols react as nucleophiles and the bond between C-O is broken when
they react as electrophiles. The chemical properties of any given aliphatic alcohol depend
on the nature of the alkyl group and on the properties of the hydroxyl group. Based on the
cleavage of O-H and C-OH bonds, the reactions of alcohols may be divided into two
groups:

(A) Reactions involving cleavage of O-H bond

1. Acylation of alcohol: When alcohol reacts with acylhalide and anhydride

substitution of hydrogen atom by acyl group is known as acylation of alcohols.

+
ROH + CH3COCl ROCOCH3 HCl

ROH + (CH3CO)2O ROCOCH3 + CH3COOH

(B) Reaction involving fission of R—OH bond (cleavage of C—O bon d): The
reactions involving R – OH bond with cleavage of C – O bond are as follow

1. Dehydration: (a) Intramolecular dehydration (forming alkene): Alcohols

undergo dehydration to form unsaturated hydrocarbon on treating with a protic acid
e.g., con. H2SO4or H3PO4, or catalysts such as anhydrous ZnCl2or Al2O3. In this
reaction the OH and an H groups removes from an adjacent carbons. Since water is
removed from the alcohol, this reaction is known as a dehydration reaction (or an
elimination reaction). Secondary and tertiary alcohols are dehydrated under much milder
conditions. The conditions for dehydrating alcohols depend closely on the structure of
individual alcohols.

For primary alcohols, the conditions required are conc. sulphuric acid and temperature
0
of 170 C.
 +
H
+
ROH ROH R + alkene
2
+
- H
H
CH3CH2CH2CH2OH CH CH CHCH
3 3

CH3 +
H
C CH2OH CH3 C CH CH3
CH3
CH3 CH3
+
CH2OH2
CH2OH H+

In smaller ring always ring expansion takes place due to molecular strain and they
tend to convert to high stability with large ring.

Secondary alcohols dehydrate under milder conditions than primary alcohols.

OH

H3PO4
+ H2O
_ 0
160 170 C

Tertiary alcohols dehydrate under even milder conditions.

C H3 20 % H2SO4
H3 C C C H2
H3C C OH
CH CH 3
3

The main function of the acid is to transform the poor leaving group — OH into the very
good leaving group —OH 2 . The order of the relative ease of dehydration of alcohols is:
0 0 0
3 >2 >1
Tertiary carbocations are most stable and therefore are easier to form than secondary and
primary carbocations; tertiary alcohols are the easiest to dehydrate.

The order of stability of th e carbocations is:

CH3 CH3 H H
CH3 C CH3 C CH3 C H C
CH3 H H H

Dehydration of secondary and tertiary alcohols containing more than three carbon atoms
will give a mixture of alkenes, the major product can be deteermined from Satzeff’s
Rule:

Satzeff’s Rule — When an alkene is produced in an elimination reaction, the major

product is the one with the more highly substituted double bond i.e., the major product is
that contains the higher number of alkyl groups attached to the C=C bond. e.g.

Rearrangement of the alkyll

groups of alcohols is very common in dehydration, particularly in the pres ence of strong
acids, which are conducive to carbocation formation. Typical examples showing both
methyl and hydrogen migr ation follow:

Mechanism:

(b)

Intermolecular dehydratioon (forming ether):

0
When the dehydration is carried out at a temperature of 140 C with an excess of alcohol
ether will be formed. Thiss reaction removes a molecule of water from two alcohol
molecules, causing the two ―R‖ groups to become att ached to an oxygen a tom,
forming an ether functional group:
 2 Con.H 2SO4
CH3CH2OH +
CH3CH2 O CH2CH3 HO
2

2. Halogenation: Alcohols can be converted to alkyl halides using one of three

reactions:

(a) Reaction with hydrogen halides: Respective alkyl halides are formed by reacting
with the appropriate hydro gen halide, HCl for chlorination, HBr for bromination, and HI
for iodination. The rea ction involves the initial protonation of the hydroxyl group of the
alcohol. This improves the leaving group ability of the hydroxyl group.

HCl
R Cl + H2O

HBr
R OH R Br + H2 O

HI
R I + H2 O

Mechanism:

Step1: Protonation of the alcohols: The alcohol acts as a weak base an d accepts the
proton donated by the hydrogen halide.
 3 3
ROH + PBr3 RBr + H PO
3 3
3 3
ROH + PI RI + HPO
3 3 3

ROH + + +
H R O H
H
Step 2: Removal of a water molecule and formation of halide through SN2 mechanism/
SN1 mechanism as:

(i) For primary and secondary alcohols, it is a SN2 reaction.

+
R-CH 2-X
X RCH2O H
H

(ii) For tertiary alcohols, it is a SN1 reaction.

R
+
+
R3C O C
H
R R
H

R
R
+ C
X C R
R R X R
0 0 0
(iii) Rate of the reaction for 1 , 2 and 3

alcohols: The order of rates of reaction:

0 0 0
3 alcohol > 2 alcohol > 1 alcohol

The rate can be shown by the turbidity in the aqueous layer since the chloroalkane
formed is immiscible with water.
(b) Reaction with thionyl chloride, SOCl2: Alcohols will react with thionyl chloride
to produce alkyl halides. The reaction involves a nucleophilic attack of the alcohol on
a SOCl2 molecule displacing one of the chlorides. Then the chloride will act as the
nucleophile in a second step and displace the oxygen from the carbinol carbon.

R OH + SOCl
2 R Cl + SO2 + HCl
(c) Reaction with phosphorus halides

Alcohols will react with phosphorus tribromide or phosphorus pentabromide to form

alkyl bromides.

The mechanism is very similar to the thionyl chloride reaction. The alcohol acts as the
nucleophile and displaces a halide ion from the PX3 or the PX5.

R-OH + P C l5 R-Cl+ H C l + P O C l3
3. Esterification: Alcohol reacts with carboxylic acids, acid chlorides and acid
anhydrides to form esters. The reaction with carboxylic acid and acid anhydride is
reversible, and therefore, water is removed as soon as it is formed. Esterification takes
place much faster in the presence of a catalyst such as conc. H2SO4.

Example :

O
Con.H2SO4
CH3CH2COOH + CH3CH2OH CH3CH2 C OCH2CH3 + H2O
Reflux

Alcohols can also react with acid chlorides and acid anhydrides to form esters. The
introduction of acetyl (CH3CO) group in alcohols or phenols is known as acetylation.

Example:
O O
+ + HCl
CH3CH2 C Cl CH3CH2OH CH3CH2 C OCH2CH3

O
O
CH3CH2 C Con.H SO
2 4

O+CH 3
CH OH
2
CH3CH2 C OCH2CH3 + CH3CH2COOH
CH3CH2 C
O
 3. Oxidation: Alcohols can be oxidized by various oxidizing agents to aldehyde, ketones
or carboxylic acids. Oxidation is the gain of oxygens and /or the loss of
hydrogens.
OH
O
[O]
C C
oxidising agent
H

0
(a) 1 alcohol oxidizes readily, first to an aldehyde, then to a carboxylic acid. These two
oxidation steps make sense because the primary alcohol functional group has two C-H
bonds that can be broken. Primary or secondary alcohols can be oxidized to produce
compounds containing the carbonyl group (a carbon-oxygen double bond, C=O). Strong
oxidizing agents such as hot alkaline KMnO4 or CrO3 in H2SO4 will oxidize primary
alcohols right past the aldehyde to the salt of the carboxylic acid in which the acid may be
precipitated by acidification. The alcohol, aldehyde and acid retain the same number of
carbon atoms.

O
[O]
RCH2OH R C H+H2O
oxidising agent

O
[O]
CH3CH2OH CH3 C H+H2O
oxidising agent

O
[O]
CH2OH C H
oxidising agent
0
b. 2 alcohol has only one C-H bond that can be broken, so it can only oxidize once, to a ketone,
which cannot be oxidized any further:
 H
R
R C OH
_2 H C O
R' R'

0
3 alcohol Ketone

OH O O
[O] [O]
CH3 CH CH3 CH C CH CH3 C OH+HO
3 3 2

OH O
[O]
+ H2O

0
c. 3 alcohol has no C-H bonds that can be broken, so it is not oxidized, no matter how
strong the oxidizing agent because it would involve the breakage of the high energy
C—C bonds in the alcohol molecule.

CH3
[O]
CH3 C OH No oxidation product
CH3

0
In acidic solutions, 3 alcohols can he oxidized to give a mixture of ketone and acid,
both with fewer carbon atoms than the alcohol.

CH3 O
[O]
+
CH3 C OH CH3 C CH3 CH COOH
3

CH2CH3

Characterization of the oxidation products of alcohols is a means of distinguishing

between primary, secondary and tertiary alcohols.

DIHYDRIC ALCOHOLS:
These compounds contain two hydroxyl (–OH) groups in a molecule. These are
dihydroxy components of alkanes. Their general formula is CnH2n+2O2. The simplest
and most important dihydric alcohol is ethylene glycol. They are classified as α, β,γ.....
glycols, according to the relative position of two hydroxyl groups. α is 1, 2 glycol, β is
1, 3 glycol.
CH2 OH
CH2 OH
CH2
CH2 OH
CH2 OH
 Nomenclature: For naming polyhydric alcohols, the name of the alkane is retained and
the ending -e is not dropped but add a di- or tri- prefix to the –ol suf fix. Thus dihydric
alcohols are named as alkane diols and trihydric alcohols are named as alkene triols.
OH
CH2 OH
OH OH
CH2 OH CH3 CH CH2 CH CH3
OH
eth - 1,2 - diol trans - 1,2 - cyclobutanediol , - pentadienol
24

OH
2 4
HO 6 7
1 3 5

, -
3 3 - diethyl 1,6 - heptanediol

METHODS OF PREPARATION

Dihydric alcohols are prepared by following different methods:

From ethylene: (a) through icy dilute alkaline solution of Bayer's reagent.

CH2 Ag 200
(i)
dil.KMnO4
(c) With HOCl followed by
(ii) OH hydrolysis:
C C

RCOOH

(b) With O2 in presence of Ag :

CH2 - catalyst
1
+ 2 O2
_ 0
400 C
 C C
OH OH
syn hydroxilation H2O CH2 OH
dil.HCl CH2 OH
OH O
OH/H
C C
O OH

anti hydroxilation
CH2 CH2 OH
+ HOCl NaHCO3 CH2 OH

+
CH2 CH2 Cl CH2 OH NaCl + CO2

From 1, 2 dibromo ethane :

CH2 Br + CH2 OH
Na2CO3 + HO 2
+ CO
CH2 Br 2
+
NaBr 2
CH2 OH

CH2 Br CH COOH CH2

+
2
CH COOK 3 CH2COOCH3 NaOH OH 2
3
2 +
CH 2 Br - KBr CH COOCH CH2 OH
CH3COONa
2 3

PHYSICAL PROPERTIES OF DIHYDRIC ALCOHOL

Dihydric alcohol viz; glycerol exhibits the following physical properties:

 (i) It is a colourless, syrupy liquid and sweet in taste. Its boiling point is 197° C.
0C
melting point -11.5

(ii) It is miscible in water and ethanol in all proportions but is insoluble in ether.

(iii) It is toxic as methanol when taken orally.

(iv) It is widely used as a solvent and as an antifreeze agent.

CHEMICAL REACTIONS OF VICINAL GLYCOLS

0
Glycerol molecule is made up of two 1 alcohol groups joined together its chemical
0
reactions are, therefore those of 1 alcohols twice over viz;

0
1. Action of Sodium: It reacts with Na at 50 c to form to form mono and dialkoxide
at elevated temperature.
0 +
CH2 OH 50 C CH 2 ONa 1
+ Na + 2
H
2

CH2 OH CH2 OH

+ 0 +
CH2 ONa
+ Na
160 C CH 2 ONa 1
+ H
CH2 OH CH2 ONa + 2 2

2. Reaction with HC: Ethylene dichloride is formed in two successive steps at

elevated temperature

CH2 0 CH2
OH+ HCl 160 C Cl
CH2 OH CH 2 OH
+H 2
O

CH2 Cl 200
0 C
CH 2 Cl
+ HCl +
CH2 OH CH2 Cl H2 O

3. Action with phosphorus halides : ethylene dihalides are formed as follow:

CH2 OH CH 2 Br
3 + PBr 3
3 2
+
H3PO4

CH2 OH CH2 Br
PI3 produce ethylene diodide which is unstable and split into I2= and ethylene

CH2 OH PI3 CH2 I CH2

+

+ I2

CH2 OH CH2 I CH2

4. Reaction with carboxylic acid: Gives diester depending upon the amount of glycol
and acid taken:

CH2 OH
+ CH3COOH CH2 OCOCH3
+ H2O
CH2 OH CH2 OH
glycol monoacetate

CH2 OCOCH3
+ CH3COOH H2SO4 CH2 OCOCH3
CH2 OH in excess CH2 OCOCH3
glycol diacetate
With dibasic acid it form polymer:
CH2 OH O O
HOOC HO
COOH + n
C C OCH CH O H
n H2O 2 2 n
OH
n CH2
terylene
trephthalic acid

5. Reaction with aldehyde and ketones: Glycol reacts with aldehyde and ketones in
presence of p- toluene sulphonic acid to give cyclic acetals/ketals which further
may give ketone/aldehyde while treating with HIO4. This reaction thus can be
useful to protect carbonyl group.

R
CH2 OH + O C O R
CH2 OH H C +H2O
O H

R
CH2 OH + O C O R
C +
H2O
CH2 OH R O R

O R R
HIO4 2
C CHCO + O C
O R R
6. (i) The oxidation of ethylene glycol with HNO3 to yields anumber of substance as
follow:
CHO
CHO
glyoxal CHO
COOH
CH2 OH CHO
COOH
CH2 OH CH2 OH COOH
glycol glucollic
aldehyde glyoxylic acid oxalic acid
COOH
 CH2 OH
glycollic acid
(ii) Oxidation with KMnO4 or K2Cr2O7 to form formic acid:

CH2 O
OH KMnO4
CH2 OH or K Cr O
2 H C OH
2 2 7
glycol
(iii) Oxidation with Pb (OCOCH3)4 or HIO4 glycol gives formaldehyde.

CH2 OH O
Pb(OCOCH3)4
CH2 OH 2H C H
glycol or HIO4

7. Dehydration: (i) Heating wih ZnCl2 glycol gives acetaldehyde

CH2 OH
ZnCl2
CH2 OH CH3CHO + HO
2
glycol
0
(ii) When heated alone at 500 C, it gives ethylene oxide.

CH2 OH
heat O
CH2 OH + HO
2
glycol
(iii) Dioxane is obtained when glycol is heated with conc. H2SO4.

HO CH2 CH2 OH
CH2 CH2
H2SO4 +2
+ O O H2O
HO CH2 CH2 OH CH2 CH2

Uses of ethylene glycol:-

1. It is used as antifreeze substance which prevents the freezing of water in car

radiators in cold countries.

2. Due it has a high viscosity, so it is used in the hydrolic break , printing ink ball,
pen inks, organic solvents .

3. Used in the manufacture of Dacron, dioxane etc.

 4. As a solvent and as a preservatives.

5. As a cooling agent in aeroplanes.

6. As an explosives in the form of dinitrate.

7. Large amounts of ethylene glycol are converted to polymers ( such as polyethylene

glycol ) used in The manufacture of dacron fibers ,photographic films and cassette
tapes.

TRIHYDRIC ALCOHOL

It is a triol. The introduction of third –OH group in diol molecule raises the b.p. about
0
100 C, increase viscosity and make the alcohol more sweet. Viz; glycerol
CH2OH

CHOH

CH2OH

It is desigbated as prop-1, 2, 3-triol in IUPAC nomenclature. It may be considered as

derivative of propane, obtained by replacement of three hydrogen atoms from different
carbon atoms by three hydroxyl group. In industry, it’s known as glycerine. It occurs
as glycosides in almost all animal and vegetable oils and fats.

METHODS OF PREPARATION

Glycerol can be synthesized by following different methods:

1. From fats and oil: On hydrolysis of fats and oils, glycerol and higher fatty acids are
formed.

CH2OOCR CH2OH
+
CHOOCR 3HO + 3
2 CHOH RCOOH
CH2OOCR CH2OH
2. By fermentation of sugars: Alcoholic fermentation of sugar in the presence of
sodium sulphite gives good yield of glycerol.

CH2OH
yeat CHOH
CH O + CH3CHO + CO2
6 12 6

3. Synthesis (from propene): Today much of glycerol is obtained from propene.

 CH3 CH Cl CH OH CH2OH CH OH
Cl2 2 dil NaOH 2 HOCl dil NaOH 2
CH CH CH CHCl CH OH
600 0C

CH2 CH2 CH2 CH2OH CH2 OH

Physical properties: Glycerol is a colourless, odourless, viscous and hygroscopic

liquid, sweet in taste and non-oxic in nature.
It is soluble in water and ethyl alcohol but insoluble in ether.
It has high boiling point, i.e., 290°C. The high vi scosity and high boiling point of
glycerol are due to association through hydrogen bonding purified in the lab by
reduced pressure distillation or vacuum distillation.

CHEMICAL REACTIONS
0 0
Glycerol molecule contains two 1 – OH groups and one 2 – OH group. Thus, it
shows characteristics of both primary and secondary alcohols.

Primary alcoholic group CH2OH

Secondary alcoholic group CHOH
Primary alcoholic group CH2OH

0 0
In general, 1 – OH groups are more reactive than 2 – OH group.

1. Reaction with sodium: Only primary alcoholic groups are attacked one by one and
secondary alcoholic group is not attacked, Sodium forms monosodium glycerolate
at room temperature and disodium glycerolate at higher temperature.

CH OH CHONa CH2ONa
2 Na 2 Na
CHOH CHOH CHOH
Room tem. High tem.
CH OH CHOH CH2ONa
2 2

2. Reaction with PCI5: All three OH groups are replaced by Cl atoms.

CH2OH CH2 Cl
+
CH2OH + PCl5 CH Cl 3 POCl 3
3 + HCl
CH2OH CH2 Cl
3. Reaction with HCI or HBr: When HCI is passed into glycerol at 110°C, both , α or
β glycerol monochlorohydrins are formed. If the HCI gas is passed for sufficient
time, glycerol α, α’ dichlorohydrin and glycerol, α,β- dichlorohydrin are formed.
 CH2 OH 0 CH2 Cl CH2 OH
110 C
CH OH + HCl CH OH + CH Cl

CH2 OH CH2 OH CH2 OH

CH2 Cl CH2 Cl
CH OH + CH Cl Excess of HCl
0
CH2 Cl CH2 OH 110 C
Same reactions occur with HBr.

4. Reaction with HI: Glycerol reacts with HI intwoways:

(a) When glycerol is warmed with a small amount of hydrogen iodide, allyl iodide is

formed. First tri iodide is formed but due to large size of iodine atom I2 comes out
from product.

CH2OH CH2I CH2

CH +I2
CHOH + 3 HI CHI
CH2OH CH2I CH2I

(b) When glycerol is heated with a large amount of HI, the allyl iodide first formed is
reduced to propene, which in presence of excess of HI forms iso-propyl iodide.
CH2 CH3 CH3 CH3
CH + HI CHI _
I
CH +HI CHI

CH2I 2
CH2I CH2 CH3
5. Reaction with HNO3: When one part of glycerol in a thin stream is added to three
times conc. HNO3 and five parts of concentrated sulphuric acid, nitro-glycerine
(glyceryl trinitrate) is formed.

CH2OH CH2 ONO2

Con. H2SO4 ONO + 3
CH
CHOH + HNO3 2 HCl
CH2OH CH2 ONO2
Glyceryl trinitrate is a yellow oily liquid. It is poisonous and causes headache. It
explodes violently when heated rapidly or subjected to sudden shock. It becomes a
safer explosive when absorbed on kieselguhr. In this form, it is known as dynamite.
Dynamite was discovered by Alfred Nobel in 1867.

6. Reaction with acetic acid, acetic anhydride or acetyl chloride: Mono-, di- and tri-
esters are formed.
 CH2OH CH2OCOCH3 CH OCOCH
CH3COOH CH3COOH 2 3
CHOH CHOH CHOH
or CH3COCl or CH3COCl
CH2OH CH2OH CH OCOCH
2 3

CH2OCOCH3
CHOCOCH3
CH2OCOCH3

7. Reaction with oxalic acid: Different products are formed under different
conditions.
0
(a) At 100 C and with excess of oxalic acid, formic acid is formed
O
CH2OH CH2O C
CH OOCH
2

_
100 110 0
C

CHOH + HOOC COOH _ CHOH

H2O CHOH C OH _CO2
CH2OH CH OCOCH
CH2OH O 2 3

CH2OH H2 O
CHOH
HCOOH +
CH2OH
0
(b) At 260 C allyl alcohol is formed
CH2OH CH2OOC CH2
CHOH+ HOOC COOH CHOOC_
_2H O 2CO2 CH
2
CH2OH
CH2OH CH2OH
8. Dehydration: Glycerol when heated alone or with dehydrating agents such as
potassium hydrogen sulphate or phosphorus penta oxide or conc. sulphuric acid,
acrolein or acrylaldehyde is formed which has a characteristic bad smell. This
reaction can be used as a test of glycerol.

CH2OH CH2
2
CHOH KHSO4 or CH + HO
2

P2O5 heat
CH2OH CHO
 9. Oxidation: Glycerol gives different oxidation products depending on the nature of
oxidizing agent. The following products may be obtained during oxidation of
glycerol.

CH2OH CH2OH COOH

[O] [O] CHO
CHOH CHOH H
COO COO
CH2OH CHO H H
glyceraldehyde glyceric acid
CHOH [O] tartonic acid
CH2OH CH OH COOH
2
glycerol [O]
CO CO [O]
COOH
CH2OH
dihydroxyacetone mesoxalic acid

(a) Dilute HNO3 gives mainly glyceric acid.

(b) Conc. HNO3 oxidises glycerol into glyceric acid and tartronic acid.

(c) Bismuth nitrate gives mainly meso oxalic acid.

(d) Fenton’s reagent (H 2O2 + FeSO4) or NaOBr or Br2- water in presence of

Na2CO3 oxidises glycerol into a mixture of glyceraldehyde and dihydroxy
acetone (or glycerose).

10. Formation of resin: Glycerol reacts with phthalic anhydride forming polyesters
known as glyptals. Each of the three –OH groups in glycerol forms an ester
linkage with the anhydride, giving a thermosetting polymer (plastic) used for
making synthetic fibers.
 O

C CH CH2 OH
n O+HO CH2
OH
C
g ly c e r o l
O
p h th a lic a n h y d r id e

O O
O
C C
CH CH2 O C
O CH2
O
O C
C O
O

C O
O
glyptal

Uses: Glycerol is used: Glycerol is used as a sweetening agent in confectionery,

beverages and medicines being non-toxic in nature. It is used as antifreeze in automobile
radiators, in the preparation of good quality of soap, hand lotions, shaving creams, tooth
pastes and cosmetics and as a lubricant in watches and preservative.

1.16 TERMINAL QUESTION

Q. 1. Explain why Alcohols are acidic in nature.

Q. 2. Write the mechanism of dehydration of ethyl alcohol with conc. H2SO4.

Q. 3.Why boiling point of alcohols is higher than that of alkanes of corresponding

molecular weight.

Q. 4. Explain why polarity of primary alcohol is maximum?Q.5.Write the major

product(s) of the following reaction.
CH3
SOCl2
HO pyridine
CH2CH3
H
 CH OH
2 PBr3

CH2OH
CrO3
H2SO4

OH PBr3

Q.6. Write short note on:-

1. Satuzaff’s rule

2. Glyptal

3. Amphoteric nature of alcohols

4. Synthesis of glycerol

5. Applicatoions of glycol and glycerol

6. Classification of monohydric alcohols

7. Oxidation of glycol and glycerol

Q.8. Tick the appropriate option (MCQs)

1. Ethanol containing some methanol is called

A. Absolute sprit B. Rectified sprit

C. Power alcohol D. Methylated sprit

2. Glycerol is a:

A. Primary alcohol B. Monohydric alcohol

C. Secondary alcohol D. Trihydric alcohol

3. Which of the following can work as a dehydrating agent for alcohols?

A.H2SO4 B.Al2O3
C.H3PO4 D. All.

4. Primary and secondary alcohols on action of red hot copper give

A. Aldehydes and ketons respectively B.Ketones and aldehydes respectively

C. Only aldehydes D.Only ketones

5. Which one has highest boiling point?

A. Butan-2-ol B.Ethane

C.Butane D.Pentane

6. Which of the following has maximum hydrogen bonding?

A. Ethyl amine B.Ammonia

C. Ethyl alcohol D.Diethyl ether

7. What is the product of the following reaction?

O

H2, Pt
A.Cyclohexanol B.Cyclohexane

C. Cyclohexene D. 1,2-cyclohexanediol

8. What is the product of the following reaction?

O (i) L iA lH 4
?
(ii) H 2 O

OH O

A. B.

OH
C. D.
9. What is the product in following reaction?.

O
NaBH4
?
H
CH3CH2OH

A. OH B.

C. OH D.

10. What is the IUPAC name of the compound below?

OH

A. 5,5 – dimethyl-2-hexanol B. 5,5-dimethyl- 2- pentanol C.2,2- dimethyl-5-

hexanol D. 2,2-dimethyl-5-pentanol

11. What is IUPAc name of the following compound ?

OH

A. 3-isobutyl-2-hexanol B. 2-methyl-5-propyl-6-heptanol C. 2-methyl-5-(1-

hydroxyethyl)octane D. 6-methyl-3-propyl-2-heptanol

12. What is the IUPAC name of the following

compound? CH3

OH
A. cis-3-methylcyclohexanol B. cis-5-methylcyclohexanol

C. trans-3-methylcyclohexanol D. trans-5-methylcyclohexanol

13. Identify the tertiary alcohol.

OH
A. B.

OH
OH
OH OH
D.
C.

OH
14. What is the hybridization of the oxygen atom in alcohols?
2
A. sp B. sp
3 3
C. sp D. sp d

15. The compound found in Whisky, Brandy & Bear:

A. CH3OH B. CH3CH2OH

C. CH3CH2CH2OH D. CH3CH2CH2CH2OH

16. Which of these five-carbon alcohols would you expect to be most water soluble?

OH
A.
OH B. C

D. OH
C. OH

17. Which is the major product of the following reaction?

 O
NaBH4
C H

O
A. C OH B. CH2OH

O
C H D. CH2OH
C.

18. Which is the major product of the following reaction?

O +
Ether HO
+ 3

C CH3 CH3MgBr

OH OH
A. B.
C CH2 CH CH3
CH3
CH3

OH
C. CH
D. CH CH2CH3
CH2OH
CH3

19. Arrange the compounds in order of increasing solubility in water (least first).

O OH
O
CH3CH2CH2C H CH3CH2CH2CH2 CH3CH2CH2CH2CH3 CH3CH2CH2CH3
I II III IV

A. II, I, IV, III B. I, II, IV, III

C. III, IV, I, II D. II, I, IV, III

20. Dynamide is:

A. Nitroderivative of glycerol B. Nitro derivative of glycol

C. Acetyl derivative of glycerol D. Acetyl derivative of glycol

1.17 ANSWERS(MCQs):

2.D 2.D 3.D 4.A 5.A 6.C 7.C 8.C

9.C 10.A 11.D 12.C 13.D 14.C 15.B 16.B

17.B 18.A 19B 20.B

1.18 REFERENCES
th
1. Jerry march, Advanced Organic Chemistry, 4 edition, Wiley India, 2010.
nd
2. P.S. Kalsi, Organic Reactions and their Mechanisms, 2 edition, New
age International Publishers. 2017
3.S.M. Mukherji and S.P. Singh, Reaction Mechanism in Organic Chemistry.
Trinity Press, 2016

4. Goutam Brahmachari, Organic name Reactions, Narosa publishing house,

New Delhi. Revised version: 2012.
th
5.I.L. Finar, Organic Chemistry, Vol. II. 5 edition, ELBS & Longman group
Ltd., 1974.
th
6. Organic chemistry, R.T.Morrision and R.N.Boyd, 6 edition, Prentice Hall
Private Ltd. 1997.
th
8. Advanced Organic Chemistry, F.A. Carey and R.J. Sundberg, Plenum. 5
Edition, 2007
9. B.S Bahal and Arun Bahal Advanced Organic Chemistry,1993, S. Chand &
Company Ltd. Ram Nagar, new Delhi