Chapter 10 Haloalkanes and Haloarenes Short Notes pdf
Haloarenes : ArX where Ar is arene and halogen attached to sp 2 hybridised carbon atom.
X is halogen atom.
Aliphatic halogen derivatives are called alkyl halides or haloalkanes. Aromatic halogen derivatives are called Aryl halides or haloarenes.
Haloalkanes and haloarenes are obtained by the replacement of a hydrogen atom of an alkane and arene respectively by a halogen atom.
A. Methods of Preparation Haloalkanes
1. From Alcohols
Groove's Process - Primary and Secondary alcohols by treatment with HCl gas in the presence of anhydrous Zinc chloride give chloroalkanes
Other methods involve reacting alcohols with KI/Phosphoric acid
Alcohols react with Phosphorous pentahalides or trihalides to form alkyl halides
Best method for obtaining haloalkanes from alcohols is to react alcohols with thionyl chloride
2. From Hydrocarbons
Alkanes undergo Free radical Substitution by Reacting with chlorine or bromine in the presence of sunlight. Propane or other higher alkanes give mixture of alkyl halides and methane undergo substitution to give chloromethane which finally form Carbon tetrachloride.
Substitution of Allylic hydrogen by chlorine atom
Toluene gives Benzyl chloride in free radical substitution with chlorine.
Alkenes react with Halogen Acid ( HCl or HBr ) according to Markovnikov's Rule
Reaction of alkenes with bromine in carbon tetrachloride is used as test for detection of unsaturation as red brown colour of bromine disappear in the reaction.
3. By Halogen Exchange Method
4. From Silver Acetate
B. Methods of Preparation of Haloarenes
1. Direct Halogenation of Arenes
2. From Diazonium Salt ( Benzene diazonium chloride )
C. Physical Properties of haloalkanes and haloarenes
D. Chemical Properties Haloalkanes
1. Nucleophilic Substitution Reactions
2. Elimination Reactions
3. Reactions with Active Metals
4. Reduction
Watch lecture 04 on Nucleophilic Substitution Reactions
Types of Nucleophilic Substitution Reactions
SN1 & SN2 Reactions and Order of reactivity of Haloalkanes towards Nucleophilic Substitution
Substitution Nucleophilic Bimolecular
Substitution Nucleophilic Unimolecular
E. Stereochemistry :
Optically Active Compounds, Enantiomers, Racemic Mixture
F. Chemical Properties of Haloarenes :
Haloarenes are less reactive than haloalkanes because of Partial double bond character in Carbon-Halogen bond and sp2 hybridisation of Carbon atom bonded to Halogen. Partial double bond character is explained by resonance structures of chloro benzene.
1. Nucleophilic Substitution Reactions :
Dows Process, Formation of Aniline from Chlorobenzene, Formation of Benzene nitrile from chlorobenzene
2. Electrophilic Substitution Reactions :
Friedel Craft Alkylation and acylation of chlorobenzene, nitration of Haloarenes
3. Reactions with Active Metals :
Wurtz fitting reaction, fitting reaction
4. Reduction
* Notes Mukul Sir
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