HALOALKANES

ALKYL HALIDES
 INTRODUCTION
● Halogen derivatives of alkanes obtained by replacement
of one or more hydrogen atoms with halogen atoms
● General formula: CnH2n+1X

● General representation formula: R-X, where R is an alkyl

group and X is halide(Cl, Br, I)

-H
● R-H R-X
+X
alkane haloalkane
 Classification
On the basis of number of halogen atoms :
1. Mono Haloalkanes : With only one halogen atom. Simply
called haloalkanes.
For example, CH3 - Cl (Chloromethane), CH3- CH(Br)-CH3
(2-bromopropane) etc.
2. Dihaloalkanes : With two halogen atoms. They are of
different types as,
a. Vicinal(Vic-) dihalides : They contain two halogen
atoms on adjacent carbon atoms. Eg.
CH2Cl - CH2Cl (1,2-dichloroethane)
b. Geminal (gem-) dihalides : They contain two halogen
atoms on same carbon atoms. Eg.
CH3 - CHCl2 (1,1-Dichloroethane)
3. Polyhaloalkanes : With three or more halogen atoms. Eg.
CHCl3(Trichloromethane, Chloroform), CCl4
(Tetrachloromethane or Carbon tetrachloride) etc.
 Classification of monohaloalkanes
● Primary haloalkane: Halogen atom is bonded to primary(10)
carbon atom.

● Secondary haloalkane: Halogen atom is bonded to

secondary(20) carbon atom.

● Tertiary haloalkane: Halogen atom is bonded to tertiary(30)

carbon atom.
Primary, secondary tertiary and quaternary carbon

Quaternary
carbon
 NOMENCLATURE
● IUPAC SYSTEM: halo+alkane

● Halogen is written as prefix before the suitable word

root, without space.
CH3-Cl (Chloromethane), CH3-CH2-Br(Bromoethane)
● CH3-CH2-CH2-Br (1-bromopropane)
● CH3-CH-CH2-CH3 (2-chlorobutane)

Cl

CH3-CH-CH2-CH2-Cl (1-chloro-3-methyl butane)

CH3

CH3

CH3-C-Cl (2-chloro-2-methylpropane)

CH3
 NOMENCLATURE
● COMMON SYSTEM: alkyl+halide

● Name of alkyl group is written first followed by halogen as

halide separated by space.

CH3-Cl(Methyl Chloride), CH3-CH2-I(Ethyl iodide)

CH3-CH-CH3 (isopropyl bromide)

Br
CH3

CH3-C-Cl (Tertiary butyl chloride)

CH3

CH3-CH2-CH-CH3 ( Secondary butyl bromide)

Br
 PREPARATION
1. From hydrocarbons:
Haloalkanes can be prepared from alkanes and alkenes.

a) From alkanes: Haloalkanes are prepared by halogenation

of alkanes.
The reaction in which one or more hydrogen atoms from
alkanes are replaced with halogen atoms. It occurs in
presence of uv light or high temperature.

UV light
CH4 + Cl2 CH3Cl + HCl

Methane Chloromethane
● The reaction continues in excess of halogen until
all hydrogen atoms are replaced with halogen.

● CH3Cl + Cl2 CH2Cl2 + HCl

Dichloromethane

● CH2Cl2 + Cl2 CHCl3 + HCl

Trichloromethane(Chloroform)

● CHCl3 + Cl2 CCl4 + HCl

Carbon tetrachloride

● Halogenation of alkanes follows free radical

mechanism which is said to occur in three steps.
● Bromination is a slow process whereas iodination is
reversible. So, iodination is carried out in presence of
an oxidizing agents like HNO3 or HIO3. For example,

HNO3 or HIO3
CH3-CH3 + I2 CH3-CH2-I + HI

But,
HNO3 + HI H2O + NO2 + I2

b) From alkenes: When halogen acids( hydrogen halides) are

added to alkenes, haloalkanes are obtained.

CH2=CH2 + HCl CH3-CH2-Cl

ethene chloroethane
 MARKOVNIKOV’S RULE
● Addition of hydrogen halides to unsymmetrical alkenes
follows Markovnikov’s rule.

● Statement: On adding unsymmetrical reagent to

unsymmetrical alkene, the positive part of the reagent is
bonded to that carbon of double bond which contains
greater number of hydrogen.

● CH2=CH2 (ethene) CH3-CH=CH2(propene)

CH3-CH=CH-CH3(But-2-ene) CH3-CH2-CH=CH2(But-1-ene)

Symmetrical alkenes Unsymmetrical alkenes

For example,

CH3 - CH = CH2 + H-Cl ✖ CH3 - CH2 - CH2 - Cl

Propene 1-Chloropropane
(Unsymmetrical alkene) ✔ (Minor)

CH3 - CH - CH3

Cl
2-Chloropropane
(Major)
● Explanation: The addition reaction of alkene is
electrophilic addition i.e. the positive part adds first to
give carbocation which then adds negative part to give
final product.During addition of positive part, the more
stable carbocation is formed(Stability order 30 >20 >10
carbocation) which then adds -ve part to give Markovnikov’s
product.

● 1st step:
+
CH3-CH2-CH2
+ 10 Carbocation
CH3-CH=CH2 + H
+
Propene
CH3-CH-CH3
20 Carbocation(More stable)
2nd step:

Br
+
CH3-CH-CH3 + Br - CH3-CH-CH3
More stable 2-bromopropane
carbocation (Markovnikov’s product)
 PEROXIDE EFFECT
● It is applicable for addition of HBr to unsymmetrical
alkenes in presence of organic peroxides like benzoyl
peroxide.

● Addition is just opposite to Markovnikov’s rule. It

follows free radical mechanism.

● Not used for HCl and HI because:

i. H-Cl bond too strong and cannot be broken to form free
radicals.

ii. H-I bond easily breaks but iodine free radical too
reactive and combines to form iodine molecule.
For example,

Peroxide
CH3 - CH = CH2 + H-Br CH3 - CH2 - CH2 - Br
Propene
(Unsymmetrical alkene) 1-bromopropane
(Major)
No Peroxide Anti-Markovnikov’s
product

CH3 - CH - CH3

Br
2-bromopropane
(Minor)
Markovnikov’s product
(Without peroxide)
2. From alcohols:
a) Using phosphorus tri and pentahalides(PCl3 or PCl5)
Haloalkanes can be prepared by reacting alcohols with
phosphorus trihalides and pentahalides.(PBr5 or PI5 does
not exist.

R-OH + PCl5 R-Cl + POCl3 + HCl

alcohol chloroalkane
3R-OH + PCl3 3R-Cl + H3PO3
For example,
CH3-CH2-OH + PCl5 CH3-CH2-Cl + POCl3 + HCl
Ethanol Chloroethane
3CH3-CH2-OH + PCl3 3CH3-CH2-Cl + H3PO3

● PBr3 and PI3 are unstable so they are prepared in situ by

reacting phosphorus with bromine or iodine.
For example,
P4 + 6Br2 4PBr3
3CH3-CH2-OH + PBr3 3CH3-CH2-Br + H3PO3

Similarly,
P4 + 6I2 PI3
3CH3-CH2-OH + PI3 3CH3-CH2-I + H3PO3
b) Using thionyl chloride( SOCl2):

Chloroalkanes can be best prepared by treating alcohols with

thionyl chloride in presence of pyridine.

pyridine
R-OH + SOCl2 R-Cl + HCl + SO2

pyridine
CH3-CH2-OH + SOCl2 CH3-CH2-Cl + HCl + SO2

Ethanol Chloroethane

Note: This method is considered as best method to prepare

chloroalkanes in pure state as all other products(SO2 and
HCl) are gases.
c) Using hydrogen halides
On treating alcohols with halogen acids in
presence of anhydrous zinc chloride (HCl +
Anhydrous ZnCl2= Lucas reagent), haloalkanes are
obtained.

anhydrous ZnCl2
R-OH + HX R-X + H2O
alcohol haloalkane

The least reactive HCl requires catalyst to

react with primary and secondary alcohol whereas
tertiary alcohols being more reactive don’t need
catalyst.
 anhydrous ZnCl2
CH3-CH2-OH + HCl CH3-CH2-Cl + H2O
ethanol chloroethane

CH3 CH3
CH3-C-OH + HCl CH3-C-Cl + H2O
CH3 CH3
2-methyl-propan-2-ol 2-chloro-2-methylpropane

Note : Lucas reagent(HCl + anhydrous ZnCl2) is

used to distinguish primary, secondary and
tertiary alcohol. The solution becomes turbid
as haloalkane is produced. Depending upon the
time taken for turbidity to appear, alcohol is
identified.
 30 alcohol, most reactive → immediate turbidity.
20 alcohol, less reactive → turbidity within 5 minutes.
10 alcohol, least reactive → turbidity only on boiling.

● The reactivity of alcohols follows the order,

Tertiary >Secondary > Primary > Methyl
● The reactivity of halogen acids follows the order
HI>HBr>HCl

● The mechanism is SN1 except for methyl alcohol which

follows SN2 mechanism.
● Rearrangement can be seen during product formation.

● This is a acid-catalyzed reaction that involves protonation

of oxygen(OH2+) followed by loss of water(results in
formation of carbocation).
 PHYSICAL PROPERTIES
● Lower members are colourless gases and liquids while
higher members are colourless solids.
● Insoluble in water but soluble in organic solvents like
ether, carbon tetrachloride, etc.
● Density increases with increase in atomic mass of
halogen as well as number of carbon atoms.
● They have high melting and boiling points than alkanes
of comparable mass. This is because greater polar nature
of C-X bond which increases the dipole force attraction.
● For isomeric cases, boiling point decreases with
increase in branching.
 CHEMICAL PROPERTIES
● Highly reactive compounds.
● Reactivity is due to Polarityof C-X bond( Due to the
difference in electronegativity between carbon and
halogen atom.)
𝜹+ 𝜹-
C X
● Partialpositive charge and partial negative charge
develops on carbon and halogen atom respectively.
● Undersuitable conditions, halogen separates taking
the electron pair with itself leaving carbon with
positive charge. Then nucleophile gets bonded to
positive carbon.
● Hence the major reactions of haloalkanes are
nucleophilic substitution reactions.
 FACTORS AFFECTING REACTIVITY
1. C-X bond dissociation energy: Greater the size of
halogen, less will be the bond dissociation energy.
Since iodine is the largest halogen, the bond
dissociation energy follows the order,
C-Cl > C-Br > C-I
So the relative reactivity of different haloalkanes
is in order,
R - I > R - Br > R - Cl
2. Nature of alkyl group: Alkyl groups are electron
releasing in nature. Greater is the number of alkyl
groups, higher is the polarity of C-X bond. Hence
greater will be the reactivity. So the reactivity
follows the order,
30 > 20 > 10 > Methyl halide
 NUCLEOPHILIC SUBSTITUTION REACTION
1. SN2: Nucleophilic substitution bimolecular:
● Rate depends on concentration of substrate(
Haloalkane) and nucleophile both i.e. both
are involved in rate determining step(single
step).
● Follows inversion of configuration.
● Occurs in a single step.
● Involves formation of transition state.
2. SN1: Nucleophilic substitution unimolecular:
● Rate depends on concentration of substrate only
(haloalkane) or only haloalkane is involved in rate
determining step.
● Racemic modification( inversion + retention).

● Occurs in two steps.

● Involves formation of carbocation(first step).

 COMPARISON
SN1 vs. SN2 mechanisms
Kinetics :
SN1 Rate = K[haloalkane]
SN2 Rate = K[Haloalkane] [Nucleophile]
Stereochemistry :
SN1 Both inversion and retention(racemic)
SN2 inversion only
 Reactivity order of haloalkanes towards SN1 and SN2
reaction
For SN1 reaction
30 > 2 0 > 10 > methyl halide

Reactivity decreases

For SN2 reaction

Methyl halide > 10 > 20 > 30
Reactivity decreases
 COMMON NUCLEOPHILIC SUBSTITUTION REACTIONS

1. Reaction with aq. KOH/NaOH : Formation of alcohols

On boiling haloalkanes with aq. NaOH or KOH, alcohols are
obtained.

R-X + aq. NaOH R-OH + NaX

haloalkane alcohol

CH3-CH2-Cl + aq. NaOH CH3-CH2-OH + NaCl

chloroethane ethanol

CH3-CH-CH3+ aq. NaOH CH3-CH-CH3 + NaCl

Cl OH
2-chloropropane Propan-2-ol
(isopropyl alcohol)
● Haloalkanes also produce alcohols by reacting with moist
silver oxide.
Ag2O + H2O 2AgOH

CH3-CH2-Cl + AgOH CH3-CH2-OH + AgCl

chloroethane ethanol

Q. A haloalkane ‘M’ reacts with aq. NaOH to give

isopropyl alcohol. What happens when M is heated with
sodium in presence of dry ether?
 2. Reaction with sodium alkoxide : Formation of ethers
Haloalkanes react with sodium alkoxide to form ethers.

R-X + R-ONa R-O-R + NaX

Haloalkane sodium alkoxide Ether

For example,

CH3-CH2-Cl + CH3-CH2-ONa CH3-CH2-O-CH2-CH3 + NaCl

Chloroethane Sodium Ethoxyethane

ethoxide
● This is a method of preparing ethers (by reacting
haloalkanes with sodium alkoxides) and it is
called Williamson ether synthesis.

● Sodium alkoxide is prepared by dissolving sodium

in alcohol.
R-OH + Na R-ONa + H2
For example,
CH3-CH2-OH + Na CH3-CH2-ONa + H2
Ethanol Sodium
ethoxide
 CONTD…
● Both symmetrical as well as unsymmetrical ethers can be
prepared by using this method.

CH3-Cl + CH3-CH2-ONa CH3-CH2-O-CH3+ NaCl

chloromethane sodium ethoxide methoxyethane

● Symmetrical ethers can also be prepared by reacting

haloalkanes with dry Ag2O.
2CH3-Br + Ag2O CH3-O-CH3 + 2AgBr
bromomethane methoxymethane
 Practice questions
Q. What do you mean by Williamson ether synthesis?
Explain with an example.

Q. Give an example of symmetrical ether. How can you

prepare the ether using Williamson ether synthesis?

Q. Give an example of unsymmetrical ether. How can you

prepare the ether using Williamson ether synthesis?

Q. Write the limitations of Williamson’s etherification

reaction.
3. Reaction with NaCN or KCN : Formation of cyanides
On reacting haloalkanes with alcoholic solution of sodium or
potassium cyanide, alkyl cyanides or alkanenitriles are
formed.
R-X + alc. NaCN R-C≡N + NaX
haloalkane alkanenitrile

CH3-Cl + alc. NaCN CH3-C≡N + NaCl

ethanenitrile
chloromethane
(methyl cyanide)
● The reaction of haloalkanes with alcoholic KCN or NaCN
is widely used to increase the number of carbon atom by
1.
CH3-CH2-Br + NaCN CH3-CH2-C≡N + NaBr
propanenitrile
bromoethane
(ethyl cyanide)

● Cyanides are highly useful synthetic compounds. They can

be converted into aldehydes, carboxylic acids, amides
and amines.
● With conc. HCl cyanides undergo partial hydrolysis to
produce amides(-CONH2).

Conc. HCl
CH3-CH2-CN CH3-CH2-CO-NH2
propanenitrile Propanamide
(ethyl cyanide)
 CONTD…
● Complete hydrolysis: On complete hydrolysis cyanides in
presence of dil.HCl, carboxylic acids are obtained.
O
dil. HCl
CH3-CH2-C≡N + 2H2O CH3-CH2-C-OH + NH4Cl
propanenitrile propanoic acid

● Reduction: On reducing cyanides with H2/Ni or LiAlH4,

primary amines are produced.

LiAlH4
CH3-CH2-C≡N + 4[H] CH3-CH2-CH2-NH2
Propanenitrile 1-aminopropane
 Answer the following question
1. How would you convert ethane to propanoic acid?

2. Starting from methane, prepare ethanamine.

 4. Formation of isocyanides: When haloalkanes are heated
with alcoholic AgCN, alkyl isocyanides or alkyl
carbylamines are formed.

R-X + alc.AgCN R-N C + AgX

haloalkane alkyl isocyanide
(alkyl carbylamine)

CH3-CH2-I + alc.AgCN CH3-CH2-N C + AgI

iodoethane ethyl isocyanide
● Isocyanides on complete reduction yield secondary amines.

LiAlH4
● CH3-CH2-N C + 4[H] CH3-CH2-NH-CH3

N-methylaminoethane
 Identify A and B in the following reactions

Alc. AgCN LiAlH4

1. Bromoethane A B
Also write IUPAC names.

2. What is ambident nucleophile? Give example.

5. Formation of nitroalkanes:
When reacted with alcoholic solution of silver nitrite,
haloalkanes produce nitroalkanes.
O

R-X + alc. AgNO2 R-N=O + AgX

nitroalkane
haloalkane
O
CH3-CH2-Br + alc. AgNO2 CH3-CH2-N=O + AgBr
bromoethane
nitroethane
 CONTD…
6. Formation of alkyl nitrites:
On reacting haloalkanes with aqueous sodium or potassium
nitrite, alkyl nitrites are formed.

R-X + aq. NaNO2 R-O-N=O + NaX

haloalkane alkyl nitrite

CH3-CH2-I + aq. NaNO2 CH3-CH2-O-N=O + NaI

iodoethane ethyl nitrite

 AMBIDENT NUCLEOPHILE
● Thenucleophiles which can attack electron
deficient centre from two different sites/
atoms are called ambident nucleophile.
● For example: cyanide ( CN-), nitrite ( NO-2)
etc.
● Whenattack comes from carbon of CN group,
cyanide(R-CN) is formed.
● Whenattack comes from nitrogen, isocyanide
(R - NC) is obtained.
● Similarly,attack from nitrogen of NO2 forms
nitroalkane but attack from oxygen produces
alkyl nitrite.
 CONTD…
7. Formation of esters:
Haloalkanes react with alcoholic solution of silver
carboxylate to form esters.
O

R-X + alc. R’COOAg R’-C-O-R + AgX

haloalkane ester

CH3-CH2-I + CH3COOAg CH3-C-O-CH2-CH3 + AgI

iodoethane ethyl ethanoate
 8. Formation of amines:
When haloalkanes are heated with alcoholic ammonia in a
sealed tube at about 100℃ , primary amines are formed.This
reaction is called Hoffman's ammonolysis reaction.

CH3-Cl + alc. NH3 CH3-NH2 + HCl

chloromethane aminomethane

If excess haloalkanes is present, formation of secondary,

tertiary amines and quaternary ammonium salts occur.
CH3-Cl + CH3-NH2 CH3-NH-CH3 + HCl
N-methyl aminomethane

CH3-Cl + (CH3)2NH CH3-N-CH3 + HCl

CH3
N,N-dimethyl aminomethane

CH3-Cl + (CH3)3N (CH3)4N+Cl-

tetramethyl
ammonium chloride
 ELIMINATION REACTION
DEHYDROHALOGENATION REACTION:
● Eliminationreactions are those in which two
atoms or group of atoms from adjacent carbon
atoms are eliminated to form multiple bonds.
● Haloalkanes undergo elimination reaction to form
alkenes.
● Eliminationundergoes in presence of alcoholic
alkali like KOH or NaOH.
● Thecarbon which contains halogen loses the
halogen atom while hydrogen is lost from adjacent
carbon.
● So it is called dehydrohalogenation reaction.
CONTD…
● Both 1 and 2 halopropanes give propene on
dehydrohalogenation.
● Do it yourself
CH3
CH3-C-Br + alc.KOH ?????
CH3
2-bromo-2-methylpropane

● The reactivity of haloalkanes follows the order:

3˚haloalkane > 2˚haloalkane > 1˚haloalkane
● Ifdehydrohalogenation leads to the formation of
more than one alkene, the product formation
follows Saytzeff’s rule.
● Therule states that: in dehydrohalogenation of
haloalkane, if there is possibility of two
alkenes, then the preferred product is the more
substituted alkene (that has the greater number
of alkyl groups attached to the doubly bonded
carbon atoms).
● Insimple terms, the alkene which contains lesser
number of hydrogen atoms across the double bonded
carbon atoms is the preferred product.
 Br
CH3-CH-CH2-CH3 + alc.KOH CH3-CH=CH-CH3
2-bromobutane but-2-ene
major product( 81%)

CH3-CH2-CH=CH2
but-1-ene,
minor product(19%)

(Note : alc. KOH brings about elimination reaction

however, aq. KOH brings nucleophilic substitution
reaction.)
 REACTION WITH METALS
1. Action with magnesium ( Formation of Grignard
reagent):
Haloalkanes react with magnesium in presence of dry ether
to form alkyl magnesium halide, commonly called as
Grignard’s reagent.

dry ether
R-X + Mg RMgX
alkyl magnesium halide
dry ether
CH3-Br + Mg CH3MgBr
methyl methylmagnesium bromide
bromide
2. Wurtz reaction:
On heating haloalkanes (alkyl halides) with sodium metal
in presence of dry ether, higher symmetrical alkanes (even
number) having double the carbon atoms than haloalkanes
are produced.
dry ether
R-X + 2Na + X-R R-R + 2NaX
haloalkane alkane

dry ether
CH3-Cl + 2Na + Cl-CH3 CH3-CH3 + 2NaCl
chloromethane ethane
● Q. Show similar reactions using bromoethane and
1-chloropropane.
CH3 CH3 CH3 CH3
dry ether
CH3-CH-I + 2Na + I-CH-CH3 CH3-CH-CH-CH3 + NaI

2-iodopropane 2,3-dimethylbutane

● This reaction is preferred to prepare alkanes having even

number of carbon atoms. Using different alkyl groups to
obtain odd member alkanes leads to formation of mixture of
3 different alkanes, which is difficult to separate.
3. Action with other metals:

dry ether
R-X + 2Li RLi + LiX
alkyl lithium

dry ether
CH3-Cl + 2Li CH3-Li + LiCl
chloromethane methyl lithium
2R-X + Zn dry ether R2Zn + ZnX2
dialkyl zinc

dry ether
CH3-Cl + Zn (CH3)2Zn + ZnCl2
dimethyl zinc
 REDUCTION REACTION
● Haloalkanes are reduced into corresponding alkanes when
reacted with reducing agents like Zn/HCl or LiAlH4.

Zn/HCl
CH3-Cl + 2[H] CH4 + HCl
chloromethane methane

Zn/HCl
CH3-CH2-Br + 2[H] CH3-CH3 + HBr
bromoethane ethane
USES OF HALOALKANES

● Lower members are used as solvents.

● Used as starting material to manufacture large

number of organic compounds
 POLYHALOGEN DERIVATIVE
●CHLOROFORM
●IUPAC Name: Trichloromethane
●Structure: CHCl3
 LABORATORY PREPARATION
● Principle: In laboratory, chloroform is prepared by
heating the paste of bleaching powder and water with
ethyl alcohol or acetone.

CaOCl2 + H2O Ca(OH)2 + Cl2

● Bleaching powder acts as source of Cl2 and Ca(OH)2.

● Cl2 acts as chlorinating agent as well as oxidizing

agent.
● Ca(OH)2 acts as hydrolysing agent.
 USING ETHYL ALCOHOL
● Step 1:Oxidation, Cl2 oxidizes ethyl alcohol into ethanal.
O

CH3-CH2-OH + Cl2 CH3-C-H + HCl

ethyl alcohol Ethanal
● Step 2: Chlorination, The three α-hydrogen atoms of ethanal are
replaced by Cl atoms from Cl2 to form chloral.
O O
CH3-C-H + 3Cl2 CCl3 -C - H + 3HCl
trichloroacetaldehyde
(Chloral)
 CONTD…

Step 3: Calcium hydroxide then hydrolyzes chloral to

produce chloroform.

O
Ca(OH)2 + 2CCl3-C-H 2CHCl3 + Ca(HCOO)2
chloroform calcium formate
 USING ACETONE
● Step 1: The three α-hydrogen atoms of acetone are
replaced by Cl atoms from Cl2 to form trichloroacetone.
O O
CH3-C-CH3 + 3Cl2 CCl3-C-CH3 + 3HCl
acetone trichloroacetone

● Step 2: Calcium hydroxide then hydrolyzes

trichloroacetone to produce chloroform.
O
Ca(OH)2 + CCl3-C-CH3 CHCl3 + Ca(CH3COO)2
chloroform calcium acetate
PHYSICAL PROPERTIES

● Heavy, colourless liquid.

● Boils at 61℃ and freezes at -63℃.
● Sweet smelling liquid with burning taste.
● Heavier than water.
● Sparingly soluble in water but highly soluble in
organic solvents like, benzene, ether, etc.
 CHEMICAL PROPERTIES
1. Action with air ( Oxidation):
In presence of sunlight, chloroform is oxidized by air
(oxygen) into phosgene, which is a highly poisonous gas.

sunlight
2CHCl3 + O2 COCl2 + HCl
phosgene
(carbonyl chloride)

● To prevent the oxidation of chloroform into poisonous

phosgene gas,
 CONTD…
i. Chloroform is stored in dark bottle(to cut off
sunlight) filled upto brim(to cut off air).
ii. While storing chloroform, small amount of ethanol (1%)
is added to the bottle. That’s because ethanol
combines with any phosgene formed and converts into
non-toxic diethyl carbonate.
 CONTD…
2. Action with aqueous alkali ( Hydrolysis):
When boiled with aqueous KOH, chloroform is hydrolysed
into potassium formate.
O O
KOH
CHCl3 + aq. 3KOH H-C-OH H-C-O-K+
formic acid potassium
formate

Potassium formate on acidification gives formic acid.

O O
- +
HCl
H-C-O K H-C-OH + KCl
formic acid
 CONTD…
3. Action with silver powder ( Dehalogenation):
On heating chloroform with silver powder, ethyne gas is
formed.
2CHCl3 + 6Ag CH≡CH + 6AgCl
Ethyne or acetylene

4. Action with conc. HNO3 ( Nitration):

When chloroform is heated with conc. HNO3, chloropicrin is
obtained.
CHCl3 + conc. HNO3 CCl3NO2 + H2O
chloropicrin

● Chloropicrin is used as an insecticide and also

used in tear gas.
 CONTD…
5. Action with acetone:
Chloroform reacts with acetone in presence of alkali to
produce chloretone.
O OH
KOH
CH3-C-CH3 + CHCl3 CH3-C-CH3
acetone
CCl3
chloretone

● Chloretone is used as a hypnotic ( sleep inducing) drug.

 CONTD…
6. Action with primary amines (Carbylamine reaction):
When primary amine (aliphatic and aromatic) is heated
with chloroform in presence of alcoholic solution of KOH,
isocyanide (carbylamine) having highly offensive smell is
obtained.

R-NH2 + CHCl3 + 3KOH R-N C + 3KCl + 3H2O

primary amine alkyl isocyanide
(alkyl carbylamine)

● This is used as test reaction for primary amines as well

as chloroform.
CH3-CH2-NH2 + CHCl3 + 3KOH CH3-CH2-N C + 3KCl + 3H2O
aminoethane alc. ethyl carbylamine
(Ethyl isocyanide)

NH2 N C

+ CHCl3 + 3KOH + 3KCl + 3H2O

alc.
aniline phenyl isocyanide
 CONTD…
7. Action with Phenol (Reimer-Tiemann reaction):
When chloroform is heated with phenol at (60-70)℃ in
presence of aqueous NaOH or KOH followed by acidification,
o-hydroxybenzaldehyde or salicylaldehyde is obtained as
major product.

OH OH
+
CHO
+ CHCl3 + 3KOH H + 3KCl + 3H2O
aq. (60-70)℃
salicyldehyde
Phenol
 CONTD…
8. Reduction:
In presence of Zn/HCl, chloroform is reduced into
methylene chloride whereas reduction in presence of Zn/H20
produces methane.

Zn/HCl
CHCl3 + 2[H] CH2Cl2 + HCl
ethanol
methylene
chloride

Zn/H2O
CHCl3 +6 [H] CH4 + 3HCl
methane
 CONTD…
9. Action with silver nitrate solution:
Pure chloroform does not react with aqueous AgNO3
solution. This is because C-Cl bond in chloroform is
covalent in nature and does not ionize to release free Cl-
ions. Due to this, no white ppt. of AgCl is formed.
CHCl3 + AgNO3 No reaction

However, if chloroform is impure, it contains HCl as

impurity due to its reaction with air. HCl reacts with
AgNO3 to give white ppt. of AgCl.

HCl + AgNO3 AgCl ↓ + HNO3

impurity white ppt.
 IODOFORM REACTION
● Iodoform is a yellow, crystalline compound having
characteristic hospital smell. O
● Compounds containing methyl keto group (CH3-C-) or that
can produce methyl keto group upon oxidation give
positive iodoform test.
● In this reaction, alcohols and carbonyl compounds react
with iodine in presence of NaOH solution(alkaline iodine
solution or NaOI) at (60-70)℃ to produce iodoform
crystals.
● Ethanol is the only primary alcohol that gives positive
iodoform test.
● Ethanal is the only aldehyde that gives positive
iodoform test.
 CONTD…
NaOH + I2 NaI + NaOI + H2O
O
oxidation
CH3-CH2-OH + NaOI CH3-C-H + NaI + H2O
ethanol acetaldehyde
O O
iodination
CH3-C-H + 3NaOI CI3-C-H + 3NaOH
iodal
O
hydrolysis
CI3-C-H + NaOH CHI3↓ + HCOONa
Iodoform, Sodium
Yellow crystal formate
The overall reaction can be written as,

𝚫
CH3-CH2-OH + NaOH + I2 CHI3 + NaI + H2O + HCOONa
Yellow crystalline
ppt. (hospital smell)

Similarly,
O
𝚫
CH3-C-CH3 + NaOH + I2 CHI3 + NaI + H2O + CH3COONa
Yellow crystalline
Propanone ppt. (hospital smell)
Q. Follow the same set of reactions
using ethanal, propan-2-ol and
propanone.

USES:

● Used as solvent.

● Used as preservative for biological

specimen.

● Used as laboratory reagent.

 MCQs
1. 2-chloropropane is an example of,
a. 10 haloalkane b. 20 haloalkane c. 30 haloalkane d. None
1. Isobutyl chloride is common name of,
a. 2-chlorobutane b. 2-chloro-2-methylpropane c.
2-chloro-1-methylpropane d. 1-chloro-2-methylpropane
1. Which of the following haloalkanes is chain isomer of
1-chlorobutane?
a. 2-chlorobutane b. 2-chloro-2-methylbutane
c. 1-chloro-2-methylpropane d. 2-chloropropane
1. 2-chloro-2-methylpropane is commonly called,
a. Tertiary butyl chloride b. secondary butyl chloride
c. Neopentyl chloride d. Isobutyl chloride
1. The formation of haloalkanes from alkanes follows,
a. electrophilic addition mechanism
b. Free radical substitution mechanism
c. Nucleophilic substitution mechanism
d. Electrophilic substitution mechanism
 MCQs
6. In preparation of iodoalkanes from alkanes, the role of
HNO3 or HIO3 is,

a. Catalyst b. Reducing agent c. Oxidising agent d. Promoter

7. Markovnikov’s rule is applicable to addition of HX to,

a. Alkanes b. Symmetrical alkenes c. Alcohols d.

unsymmetrical alkenes

8. Formation of alcohol from alkyl halide is an example of,

a. Electrophilic addition b. Nucleophilic substitution

c. Nucleophilic addition d. Elimination

9. The correct order of reactivity of different haloalkanes

towards nucleophilic substitution is,

a. R-Cl>R-Br>R-I c. R-Br> R-Cl> R-I

b. R-I> R-Br> R-Cl d. R-I> R-Cl> R-Br
 MCQs
10. Which of the following haloalkane is expected to undergo
nucleophilic substitution by SN2 mechanism more easily?

a. Chloroethane c. 2-chloro-2-methylpropane
b. 2-chlorobutane d. 2-bromo-2-methylpropane

11. Haloalkanes on boiling with alcoholic KOH produce

alkenes. It is an example of……………………...reaction.

a. Nucleophilic substitution c. Elimination

b. Electrophilic addition d. Free radical substitution

12. A compound ‘A’ reacts with KCN and the product on

hydrolysis produces ethanoic acid. ‘A’ is,

a. Chloroethane c. 1-chloropropane
b. 2-bromopropane d. Chloromethane
 MCQs
13. 2,2,2-trichloroethanal is commonly known as,

a. Carbylamine c. Phosgene
b. Chloral d. Freon-22

14. Tear gas contains which of the following compound?

a. Chloretone c. Chlorofluorocarbon
b. Phosgene d. Chloropicrin

15. What is the correct order of reactivity of haloalkanes

towards SN1 reaction?

a. 10 > 20 > 30 c. 30 > 20 > 10

b. 20 > 30 > 10 d. 10 > 30 > 20
1. AgCN(alc.)
16. For the reaction, CH3-Cl X. The ‘X’ is,
2. LiAlH4
a. Methyl isocyanide c. Ethanoic acid
b. Ethylamine d. Dimethylamine
 MCQs
17. Which of the following is an example of ambident
nucleophile?

a. Hydroxy c. Alkoxy
b. Cyanide d. Halide

18. 2-bromobutane is heated with alcoholic KOH. The major

product is,

a. But-1-ene c. But-2-ene
b. Butan-2-ol d. Bromoethane

19.Haloalkanes on heating with sodium metal in presence of

ether produce alkanes. The reaction is called,

a. Grignard’s reaction c. Carbylamine reaction

b. Sandmeyer reaction d. Wurtz reaction

20. Formation chloroform from ethanol in lab. does not involve,

a. Oxidation b. Hydrolysis c. dehydration d. Chlorination

 MCQs
21. Slow oxidation of trichloromethane in air in presence of
sunlight produces,
a. Methanoic acid c. Ethyne
b. Carbonyl chloride d. Chloropicrin
22. Which of the following compound reacts with chloroform in
presence of alkali produces a hypnotic drug, chloretone?
a. Nitric acid c. Propanone
b. Ethanol d. Aq. KOH
23. Which of the following is not an application of
chloroform?
a. As solvent c. in preparation of hypnotic drug
b. As anesthetic d. as oxidising agent
24. Chloropicrin, an insecticide is obtained by reacting,
a.CHCl3+ conc. HNO3 b.CHCl3+ KOH
c.CHCl3+Propanone d. heating CHCl3
 MCQs
25. Test reaction of given sweet smelling liquid whether it is
chloroform or not is,
a. Reimer-Tiemann reaction c. Carbylamine reaction
b. Wurtz reaction d. Grignard reaction
26. Iodoform has medicinal properties. It acts as,
a. Antiseptic c. Antimalarial
b. Antibiotic d. Analgesic
27. 1% ethanol is added in bottles of chloroform to,
a. Prevent oxidation of it c. make it less reactive
b. Stop Solidification of it d. convert phosgene to diethyl
carbonate
28. Propene reacts with HBr and the product is heated with Na
and ether gives,
a. 2-methylbutane b. 2-methylpropane
c. 2,2-dimethylbutane d. 2,3-dimethylbutane
 MCQs
29. The unsaturated hydrocarbon obtained by heating
chloroform with silver powder is

a. Ethene c. Vinyl chloride

b. Ethyne d. Tetrachloroethene

30. The major product in dehydrohalogenation of

2-chlorobutane is,

a. But-2-ene c. 2,3-dimethylbutane
b. 2-methylpropene d. But-1-ene

31. In SN1 reaction, the rate of reaction depends upon,

a. Nucleophile c. Alkyl halide

b. Both alkyl halide and nucleophile d. solvent used

32. Purity of chloroform can be tested with,

a. Aq. KOH c. Silver powder

b. AgNO3 d. 10 amine