Notes on lesson on Haloalkanes and Haloarenes |

Haloalkanes and Haloarenes


Defination and types of haloalkanes.

Organic halogen compound is the hydrocarbon derivatives obtained by replacing one or more atoms by the corresponding number of halogen atom.The halogen compound obtained by the replacement of one or more hydrogen atom of aliphatic hydrocarbon are known as aliphatic halogen compound.Haloalkanes are the organic compound formed by replacing a hydrogen atom by a halogen atom. They have general structure formula R-X, where R is an alkyl group and X is halogen (Cl, Br, and I). In homologous series, haloalkane is represented by CnH2n+1.X.

Nomenclature and isomerism of haloalkane

In the commons system , the mono halogen derivatives of alkanes are called alkyl halides.In the IUPIC system, the mono halogen derivatives of alkanes are named as haloalkanes, I,e the name can be obtained by prefixing the word halo to the name of the alkane corresponding to longest continuous carbon chain holding the halogen atom. Chain isomerism arises due to the different structure of carbon skeleton in the largest chain .. Position isomers are formed due to different positions of functional groups or substation

Preparation of Haloalkanes.

Alkanes are good starting material to prepare haloalkanes. When they are treated with sunlight, heat or suitable catalyst, haloalkanes are obtained. This reaction is called halogenation.$$CH_3-CH_3+Cl_2\xrightarrow{hv}CH_3CH_2Cl =(Chloro \,ethane)+HCl$$ Fluoro is not generally prepared by halogenation because it is a highly reactive element and forms carbon as.

Laboratory preparation of Chloroform.

Chloroform is a sweet smelling liquid having freezing point -630C. and has boiling point 610C. it is the colourless non-flammable liquid that is insoluble in water.On an industrial scale,chloroform is prepared by chlorination of methane.Pure chloroform is prepared by heating choral hydrate with a strong solution of caustic soda.In round bottom flask, bleaching powder paste is prepared by adding 100g of bleaching powder to 200 ml of water and crushing the residue of bleaching powder in a mortar with the help of a pestle. the solution is then filtered into 1 1000ml of the round-bottomed flask.The chloroform is then dried over anhydrous CaCl2 and redistilled between the temperature 600C-650C.

Physical and chemical property of Chloroform.

Some of the physical property are It is insoluble in water and soluble in organic solvent. Although chloroform is non-poisonous, if forms a poisonous compound (phosgene) in air.Chloroform is stored in a dark brown bottle with a tight lid so as to prevent the formation of poisonous phosgene.When phenol is heated with chloroform and aqueous alkaline at temperature 60-700C, O-hydroxy benzaldehyde (Salicylaldehyde) is formed as the chief organic product. This reaction is termed as Riemer-Tiemann reaction.

Preparation of DDT, BHC and Iodoform

DDT is a powerful contact insecticide and is widely used for killing mosquito and other insects.It is an odourless white crystalline solid with melting point 1090C. It is almost insoluble in water but readily dissolves in benzene, kerosene oil, alcohol, etc The mixture of stereoisomeric hexachlorides is an active component in BHC is γ isomer, called gammaxene or lindane.It is used as in antiseptic for dressing wounds and this nature is due to iodine that it liberates. However, of its unpleasant smell, it has now been replaced by better antiseptic.

Haloarenes and Method of preparation of Haloarenes

Haloarenes are the halogen derivatives of aromatic hydrocarbons in which halogen is directly attached to the ring. these are obtained by replacing hydrogen by alpha-halogen atom.$$Ar-H\xrightarrow{-H\,/+X}Ar-X$$ $$Where\,Ar-H=Aromatic\,substution$$