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Table of content

Nome nclature,Isomerism and classification of Monohaloalkanes.

Preparation of Haloalkanes from alkanes, alkenes and alcohols

Physical properties of Monohaloalkanes.

Chemical properties of haloalkanes : Substitution reactions SN1 and SN2 (basic concept only)

Formation of alcohol, nitrile, amine, ether, thioether, carbylamines, nitrite and nitro alkane using haloalkanes.

Elimination reaction (dehydrohalogenation, Saytzeff’s rule), Reduction reactions,Wurtz reaction.

Preparation of trichloromethane(chloroform) from ethanol and propanone
Chemical properties of trichloromethane: Oxidation , reduction , Action of silver powder , conc. nitric acid, propanone, and aqueous alkali.

Haloalkanes(Alkyl halides)

Introduction

Haloalkanes are the derivatives of hydrocarbon because they are derived by replacing hydrogen to halogen atom therefore the halogen derivatives of alkane are called haloalkanes. Or the organic compound containing halogen atom (X = -F,-Cl, -Br, -I) as functional group are called Haloalkanes.

They are also called alkyl halides.

Uses:

Solvent,Medicine,Insecticide, etc.

Haloalkanes are formed by the replacement of one or more hydrogen atom of alkane by same number of halogen atom and are bonded with carbon atom of alkane through strong covalent bond. They are presented by general molecular formula

CnH2n+1X.

Nomenclature of haloalkanes

Prefix + Word root + Primary suffix

prefix:side chain branches substitents

word root:number of C-atoms

primary suffix:nature of C-atoms (-ane or -ene or -yne)

(-X=halo,-F=fluoro, -Cl=chloro, -Br=bromo, -I=iodo)

NOTE: IF SOME WORD /LETTER OR SOMETHING IS NOT IN CORRECT FORM YOU CAN ROTATE YOUR PHONE.

Formula	Common name (Alkyl+halide)	IUPAC name (Halo +word)
R-X	alkyl halide	haloalkane
CH₃F	methyl fluoride	fluoromethane
CH₃CH₂-Cl	ethyl chloride	chloroethane
CH₃CH₂CH₂Br	propyl bromide	1-bromo propane
CH₃CH₂-I	ethyl iodide	iodoethane
CHCl₃	chloroform	trichloromethane
CHI₃	iodoform	triiodomethane
CCl₄	carbontetrachloride	tetrachloromethane
	ethylidine chloride (geminal dichloride)	1,1-dichloroethane
	ethylene dichloride (vicinal dichloride)	1,2-dichloroethane
CH₃CH₂CH₂Cl	n-propyl chloride	1-Chloropropane
	(tertiary butyl bromide) (Neo-butylbromide)	2 bromo-2-methylpropane
CH₃CH₂CH₂CH₂-Br	n-butyl bromide	1bromobutane
	iso-butyl bromide	1-bromo-2-methylpropane
	isopropyl chloride	2-chloropropane
	secondary butyl bromide	2-bromo butane

Classification of haloalkanes
[A] Onthe basisof nature of carbon atom
1. Primary haloalkane(1 ̊)
The haloalkane in which the halogen containing carbon
is further bonded to one carbon atom (one alkyl group)
or primary carbon is called primaryhaloalkane.

2. Secondary haloalkane (2 ̊)
The haloalkane in which the halogen containing carbon
is further bonded to two carbon atoms (two alkyl
group) or secondary carbon is called secondary
haloalkane.

3. Tertiary haloalkane (3 ̊)
The haloalkane in which the halogen containingcarbon
is further bonded to three carbon atoms (three alkyl
groups) or tertiarary carbon is called tertiary hal
Isomerism in haloalakanes
1.Chain isomerism
Haloalkanes having samemolecular formula but different
number of carbon chain length are called chainisomers.
CH₃CH₂CH₂CH₂CH₂-Br -->1-bromopentane(n-pentyl bromide)

1-bromo 3-methyl butane(iso pentyl bromide)
-->1-bromo-2,2-dimethylpropane(neopentyl bromide)
2.Position isomerism
Haloalkanes having same molecular formula but
different position of halogen atom on carbon chain are
called position isomers.
CH₃CH₂CH₂−Cl --> 1-chloropropane (n-propyl chloride)
--> 2-chloro propane
Self test:
Q.Write all possible isomers with molecular formula  C4H9I and give their IUPAC name.

General methods of preparation of haloalkane
1. From alkanes(Halogenationof alkanes)

The haloalkanes are prepared by treating alkane
with limited amount of halogen in presence of
halogen carrier and sunlight or heat.
R-H+X₂⟶R-X+HX
alkane haloalkane

On excess supply of chlorine polysubstituted
product areformed.
In case of higher alkanes two or more possible
products are formed.

Thebromination is carried out in presence of FeBr₃
under sunlight or heat.
The iodination of alkane is reversible reaction. So to
obtain iodoalkane strong oxidizing agent like conc.
HNO₃ or HIO₃ is used to increase the rate of
forward reaction.
Thus formed iodine increase the rate of forward
reaction. Hence the iodination of alkane must be
carried out in presence of strong oxidizing agent.

Reactivity of alkane = 3 ̊ > 2 ̊ > 1 ̊
Reactivity of halogen = F>Cl> Br > I
2. From alkenes(Hydrohalogenationof alkenes)
The haloalkanes are prepared by the reaction of
alkene with halogen acid (HF, HCl, HBr, HI). This
reaction is called Hydrohalogenation reaction.
CH₂=CH₂+HCl⟶CH₃CH₂Cl
ethene         chloroethane

If unsymmetrical alkene is taken then two possible
products are formed.       Cl
CH₃CH=CH₂+HCl⟶CH₃CHCH₃+CH₃CH₂CH₂Cl
propene                         2-chloropropane 1-chloropropane
The formation and stability of these two products
canbe explained by following two rules:
[A] Markovnikov’s rule:
According to this rule “when an unsymmetrical alkene
reacts with unsymmetrical reagent then the positive part
of reagent goes to that double bonded carbon containing
greater number of hydrogen atom”.For example
                                            Cl
CH₃-CH=CH₂ + HCl⟶CH₃-CH-CH₃
Propene                        2-chloropropane
[B] Peroxide effect (Anti- Markovnikov’s rule)
According to this rule “when an unsymmetrical alkene
reacts with unsymmetrical reagent in presence of organic
peroxide (R-O-O-R)then the positive part of reagent goes to
that double bonded carbon containing lessnumber of
hydrogen atom”. For example,

It is also called Kharasch effect.

#HCland HI do not giveAnti-Markovnikov’s addition.
H-Cl is highly polar hence does not undergo homolysis easily. HI undergoes homolysis to give iodine free radicals which instantly combine to give I2.
3.From alcohols
Generally haloalkanes are prepared by the
reaction of alcohols with haloacids or phosphorous
halide or thionylchloride.
(a) Reaction with halogen acid(HX)
The chloroalkane are prepared by the reaction
of alcohol with HCl in presence of anhydrous
zinc chloride(ZnCl₂).
The mixture of conc. HCl and anhydrous ZnCl₂ is
called Lucasreagent.

# The tertiary alcohol is more reactive. So it does not
need catalyst, i.e. anhydrousZnCl₂.
(b) Reaction with phosphorous halide (PX₅or PX₃)
The haloalkanes are prepared by the action
of alcohol with PX₅ or PX₃.
R-OH+ PX₅----△--->R-X+POX₃+HX
3R-OH+ PX₃---△--->3R-X +H₃PO₃
alcohol                    haloalkane
CH₃CH₂OH+PCl₅----△--->CH₃CH₂Cl+ POCl₃+HCl
ethanol                              Chloroethne+phosphoryl chloride
3CH₃OH +PCl₃---△--->3CH₃Cl +H₃PO₃
methanol                         chloro methane + phosphorous acid
Since, PBr₃ and PI₃ are unstable compound. So they
are prepared in reaction mixture (In-situ form) by
the action of red phosphorous with Br₂ or I₂.
P₄ + 6Br₂ ---△--->4PBr₃
CH₃CH₂OH+PBr₃ ---△---> CH₃CH₂-Br+ H₃PO₃
ethanol                                 bromoethane
similarly,
P₄ + 6I₂---△---> 4PI₃
CH₃CH₂OH+PI₃---△--->CH₃CH₂-I+ H₃PO₃
ethanol                             iodoethane
(c) Reaction with thionyl chloride(SOCl₂)
(Darzen’sreaction)
The chloroalkanes are prepared by heating alcohol
with SOCl₂ in presence of pyridine. Only chloroalkane are prepared by this method.From this method pure chloroalkane can be prepared because SO₂ and HCl evolved as gases.

Physical properties of haloalkanes
1. Lower members of haloalkane methylchloride,methyl bromide
are colorless gases, higher are colorless and sweet smelling
liquids and next higher are colorless solids.
2. They are insoluble in water and soluble in almost all
organic solvents like ether, alcohol etc.
3. They burns with green edged flame on air.
4. The boiling point of haloalkanes are higher than
corresponding parent alkanes.
5. The boiling point of haloalkane having same alkyl group is
RI>RBr > RCl due to large size of halogen atom.
6. Branched chain haloalkane havelower boiling point than
straight chain haloalkane due to spherical nature.
7. The B.P. increase as the increase in alkyl group.
Chemical properties of haloalkanes

The haloalkanes are more reactive than alkane
due to presence of polar C-X bond. The polarity
arise due to difference in electronegativity value
between carbon and halogen atom.
[A] Nucleophilic substitution reaction

The nucleophile are electron rich species
having lone pair of electron or negative charge and can attack to electron deficient centre. When a nucleophile is substituted by another nucleophile then the reaction is called nucleophilic substitution reaction.

Here, existing nucleophile has been substituted byincoming
nucleophile.
The alkyl halides undergo nucleophilic substitution
reaction (SN- reaction ) by following two mechanisms.

i. SN1 reaction:
SN1 stands for nucleophilic substitution
unimolecular. When the rate of SN depends upon the
concentration of substrate only (alkyl halide), then the
reaction follows first order kinetics and represented
as SN1. The alkaline hydrolysis of t-butyl bromide by
aq. NaOH to give t-butyl alcohol is an example of
SN1. The reaction completes in two steps.
Step 1)
Alkyl halide ionizes to give carbocation. Then step is
slow and hence it is rate determining step.

Step 2)
In the second step, the nucleophile attacks to
the carbonium ion to give t-butyl alcohol (ionic
reaction, fast)

ii. SN2 reaction
SN2- stands for nucleophilic substitution bimolecular.
When the rate of SN-reaction depends upon the
concentration of substrate (alkyl halide) and
nucleophile (Nu), then the reaction follow second
order kinetics and represented as SN2. Consider the
alkaline hydrolysis of methyl bromide by aq. NaOH to
give alcohol. It completes in one step through
formation of intermediate.