Organic Chemistry is about the reactions to form the alkanes, alkenes, alkyne, alkyl halides, and many other organic compounds. Alkyl Halides are used on a large scale in several objects used in our day-to-day life. They are used as fire extinguishers, antibiotics and many more. Alkyl Halides consist of halogen groups, which give them the property of being polar.
They are also called haloalkanes. When an alkane contains one or two halogen atoms as a substitution, it is called an alkyl halide. Fluorine, chlorine, iodine, or bromine are halogen atoms. The common formula for the alkyl halides is RX, where R is the substituted alkyl group and X is a halogen. The bond formed between carbon and halogens is polar.
Alkyl halides are divided according to the position of the halogen atom in a carbon chain. The types of alkyl halides are as follows.
When the halogen atom is attached to a carbon attached to only one alkyl group and has the first position in a chain, it is called a primary alkyl halide. CH3CH2Br is an example of primary alkyl halides.
When the halogen atom is attached to a carbon attached to two alkyl groups and has the second position in a chain, it is called a secondary alkyl halide. CH3CHBrCH3 is an example of primary alkyl halides.
When the halogen atom is attached to a carbon attached to three alkyl groups and has the third position in a chain, it is called a tertiary alkyl halide. CH3CH3CBrCH3 is an example of tertiary alkyl halides.
When the halogen is attached to the carbon atom at the sp3 hybridised with a carbon-carbon double bond, it is called allylic halide.
When the halogen is attached with the carbon atom, which is at the sp2 hybridised atom with the carbon-carbon double bond, it is called Vinylic Halides.
From alkanes
In the case of the production of haloalkanes from alkanes, the hydrogen atom is substituted with the halogen atom.eg
CH4 +Cl2+energy→CH3Cl+HCl
From alkenes
The dry hydrogen halide (HX) reacts with the alkene to form mono-haloalkane. One bond forms with halogen and the other with hydrogen. It may also react with halogens to form double halo compounds.eg
H2C=CH2 + H-Cl → H2C-CH2Cl
From alcohols
Tertiary alcohol reacts with hydrochloric acid to form tertiary chloroalkane. In the case of a primary and secondary alcohol, a catalyst like zinc chloride is required to start the reaction.eg
CH3CH2OH + HI → CH3CH2 I + H2O
Preparation of Alkyl Halides by Free Radical Halogenation
A complex mixture of isomeric mono- and poly haloalkanes is formed upon free radical chlorination or bromination of alkanes.
CH3CH2CH2CH3 + Cl2 → CH3CH2CHClCH3 + CH3CH2CH2CHCl
Halogens react with nucleophiles to form saturated hydrocarbons and the halogenated product. The reaction is a substitution type of reaction. Eg.
CH3CHBrCH3 + NaOH → CH3-CHOHCH3 +NaBr
In this reaction, the halogens and the adjacent proton get removed from the haloalkane to form an alkene. Dihaloalkanes are converted into alkenes by this reaction. This is an elimination reaction.
CH3CHBrCH3 + NaOH → CH2=CHCH3 +NaBr +H2O
Haloalkanes react with some metals to give alkyl metal compounds. For example, it undergoes a free radical reaction with magnesium to form alkyl magnesium compounds.eg
R- X + 2Na + X- R → R-R + 2NaX……( in presence of dry ether)
Thus, when an alkane contains one or two halogen atoms as a substitution, it is called an alkyl halide. Alkyl halides are divided according to the position of the halogen atom in a carbon chain, as given above. They are from the alkanes, alkenes, alkynes, biosynthesis process, alcohol, carboxylic acid, amines by executing various reaction types. It readily reacts with nucleophiles to give the saturated hydrocarbon and halogenated product. It also undergoes an elimination reaction and reaction with metals to form organometallic compounds. Also, they show many properties that are contrasting to their parents.
Do you still have questions on alkyl halides? Questions on the subject are answered below.
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