Reactions of arenes with iodine is reversible in nature. So aryl iodides are prepared in the presence of an oxideising agent such as HNO₃, HIO₄, etc., inorder to oxidise the HI formed during iodination.

R-OH \(\overset { RedP/{ x }_{ 2 } }{ \longrightarrow } \)R-X (X-Br,I)
This method is not applicable for the preparation of aryl haldies because the C - 0 bond in phenol has a partial double bond character and it is difficult to break being stronger than a single bond.

Carbylamine reaction:
Chloroform reacts with aliphatic or aromatic primary amine and alcoholic caustic potash, to give foul smelling alkyl isocyanide (carbylamines).

This reaction is used to test primary amine.

Fluoro benzene is prepared by treating benzene diazonium chloride with fluoro boric acid. This reaction produces diazoriium fluoroborate which on heating produces fluorobenzene. This reaction is called Balz - Schiemann reaction.
\(\underset { Benzene\ diazonium \ chloride }{ { C }_{ 6 }{ H }_{ 5 }{ N }_{ 2 }Cl } +HB{ F }_{ 4 }\overset { \longrightarrow }{ -HCl } { C }_{ 6 }{ H }_{ 5 }{ N }_{ 2 }BF\overset { \longrightarrow }{ heat } \underset { Fluorobenzene }{ { C }_{ 6 }{ H }_{ 5 }F+{ BF }_{ 3 }+{ N }_{ 2 } } \)

The attack of nucleophile occurs from the back side (i.e opposite to the side in which the halogen is attacked). The carbon at which substitution occurs has inverted configuration during the course of reaction just as an umbrella has tendency to invert in a wind storm. This inversion of configuration is called Walden inversion.

Reaction with alcoholic ammonia (Ammonolysis) Haloalkanes react with alcoholic ammonia solution to form alkyl amines.

However, with excess of halo alkane, secondary and tertiary amines along with quartenary ammonium salts are obtained.

i) Acetic acid: Solid carbon dioxide reacts with Grignard reagent to form addition product which on hydrolysis yields carboxylic acids.

ii) Acetone :
\(\underset { Iodomethane }{ { CH }_{ 3 }-I+Mg } \overset { dryether }{ \longrightarrow } \underset { Methyl \ magnesium \ iodide }{ { CH }_{ 3 }MgI } \)
iii) Ethyl acetate: Ethy1chloroformate reacts with Grignard reagent to form esters.

iv) Iso propyl alcohol : Aldehydes other than formaldehyde, react with Grignard reagent to give addition product which on hydrolysis yields secondary alcohol.

v) Methyl cyanide : Grignard reagent reacts with cyanogen chloride to from alkyl cyanide

Freons (CFC): The chloro uoro derivatives of methane and ethane are called freons.
Uses:
(i) Freons are a used as refrigerants in refrigerators and air conditioners. 
(ii) It is used as a propellant for aerosols and foams
(iii) It is used as propellant for foams to spray out deodorants, shaving creams, and insecticides

a) The product formed is ethylmagnesium iodide (Grignard reagent)
\({ C }_{ 2 }{ H }_{ 5 }+Mg\overset { dryether }{ \rightarrow } { { C }_{ 2 }H }_{ 5 }Mgl\)
                                 Ethyl magnesium iodide
b) The Grignard carbon is highly basic and reacts with acidic protons of polar solvents like water to form an alkani so all reagents should be pure and dry.

Alcoholscanbeconvertedintohaloalkenesbyreactingit withanyoneofthefollowingreagent
1.hydrogen halide
2. Phosphorous halides
3. Thionyl chloride
a) Reaction with hydrogen halide:
\(\underset { Ethanol }{ { CH }_{ 3 }{ CH }_{ 2 }OH+HCl } \overset { Anhydrous\\ ZN{ Cl }_{ 2 } }{ \underset { \triangle }{ \longrightarrow } } \underset { Chloroethane }{ { CH }_{ 3 }{ CH }_{ 2 }Cl+{ H }_{ 2 }O } \)
Mixture of con.HCI and anhydrous ZnCl₂ is called Lucas reagent
b) Reaction with phosphorous halides :
Alcohols react with PX₅ or PX₃ to form haloalkane. PBr₃ and PI₃ are usually generated in situ (produced in the reaction mixture) by the reaction of red phosphorus with bromine and iodine, respectively.

c)Reaction with thionyl chloride :

This reaction is known as Darzen's halogenation

If moisture is present, the Grignard reagent will react with water to give alkanes.

So. moisture should not be present

Carbon halogen bond is a polar bond as halogens are more electro negative than carbon. The carbon atom exhibits a partial positive charge (\(\delta \)+) and halogen atom a partial negative charge (\(\delta \)-)
The C -X bond is formed by overlap of sp³ orbital of carbon atom I with half filled p-orbitat of the halogen atom. The atomic size of halogen increases from fluorine to iodine, which increases the C - X bond length. Larger the size, greater is the bond length, and weaker is the bond formed. The bond strength of C - X decreases from C - F to C - I in CH₃X

Chloroform undergoes oxidation in the presence of light and air to form phosgene (carbonyl chloride)

Since phosgene is very poisonous, its presence makes chloroform unfit for use as anaesthetic.

With acetyl chloride, CH₃MgI given first acetone.

The acetone formed will react with excess CH₃MgI to give a tertiary alcohol, t - butyl alcohol.