Chemical properties
Halogenation : - CH 4 + Cl 2
UV
CH 3 Cl + HCl
UV UV
CH
UV 3 Cl CH 2 Cl 2 CHCl 3 CCl 4
Noted : - Iodination is a reversible reaction . So it is carried out by heating alkane in the presence of some oxidizing agent like iodic acid ( HIO3 ) or nitric acid ( HNO3 ) or mercuric oxide ( HgO ) which oxidizes HI formed during the reaction .
CH 4 + I 2
CH 3 I + HI 5HI + HIO 3 3H 2 O + 3I 2
2HI + 2HNO 3 2H 2 O + I 2 + 2NO 2 Noted : - Fluorination of alkane takes place explosively resulting even in the rupture of C — C bond in higher alkanes . Features of Halogenations : -
( i ) The reactivity of Halogens : - F2 > Cl2 > Br2 > I2 . ( ii ) The rate of replacement of Hydrogens of alkanes is :
CH3CH2CH2CH3 n - Butane
Cl2
hv
3 ° > 2 ° > 1 °
CH3CH2CH2CH2Cl + CH3CH2CHCH3 Cl
°
1
° °
CH3C
CH3
3 1 Cl2 Cl
° CH - CH3
1
CH3
CH3 CH3
h 36 % ( 3 °)
CH3
Isobutane CH3
CH - CH2 Cl 64 % ( 1 °)