1. Classification of Haloalkanes and Haloarenes:

2. Preparation of Haloalkanes:

(i) From Alcohols:

$R - OH + HCl \overset{{ZnCl}_{2}}{⟶} R - Cl + H_{2} O$

$R - OH + NaBr + H_{2} {SO}_{4} ⟶ R - Br + {NaHSO}_{4} + H_{2} O$

$3 R - OH + {PX}_{3} ⟶ 3 R - X + H_{3} {PO}_{3} (X = Cl, Br)$

$R - OH + {PCl}_{s} ⟶ R - Cl + {POCl}_{3} + HCl$

$R - OH \to_{x_{2} = {Br}_{2}, I_{2}}^{red P / X_{2}} R - X$

$R - OH + {SOCl}_{2} ⟶ R - Cl + {SO}_{2} + HCl$

(ii) From alkanes by free radical halogenation :

${CH}_{3} {CH}_{2} {CH}_{2} {CH}_{3} \to_{or heat}^{{Cl}_{2} / UV light} {CH}_{3} {CH}_{2} {CH}_{2} {CH}_{2} Cl + {CH}_{3} {CH}_{2} CH (Cl) {CH}_{3}$

(iii) From Alkenes by addition of hydrogen halides -

${CH}_{3} CH = {CH}_{2} + H - I ⟶ \underset{Minor}{{CH}_{3} {CH}_{2} {CH}_{2} I} + \underset{Major}{{CH}_{3} CH (I) {CH}_{3}}$

(iv) From Alkenes by addition of Halogens

$C_{2} H_{4} + {Br}_{2} \overset{{CCl}_{4}}{⟶} {BrCH}_{2} - {CH}_{2} Br$

(v) By Halogen exchange method:

(a) Finkelstein reaction:
${CH}_{3} {CH}_{2} Br + Nal \to_{heat}^{Acetone} {CH}_{3} {CH}_{2} I + NaBr$

(b) Swart's reaction:
${CH}_{3} Br + AgF \to {CH}_{3} F + AgBr$

3. Preparation of Haloarenes:

(i) From hydrocarbons by electrophilic substitution :

(ii) From amines by Sandmeyer’s reaction :

4. Nucleophilic substitution reactions :

(i) The reactivity of alkyl halides towards $S_{N} 2$ mechanism is: methyl $> 1 ° > 2 ° > 3 °$ .

(ii) The $S_{N} 1$ mechanism occurs through the formation of carbocation. The order of reactivity is: $3 ° > 2 ° > 1 ° >$ methyl

5. Reaction with metals (Wurtz reaction):

$C_{2} H_{5} Br + 2 Na + C_{2} H_{5} Br \overset{Dry ether}{\to} {CH}_{3} {CH}_{2} {CH}_{2} {CH}_{3} + 2 NaBr$

6. Reduction: $C_{2} H_{5} Br \to_{Zn / Cu couple or Sn / HCl}^{H_{2}, Ni or HI, red P or} C_{2} H_{6} + HBr$

7. Elimination reactions: $C_{2} H_{5} Br \overset{alc . KOH}{\to} \underset{alkene}{{CH}_{2} = {CH}_{2}} + HBr$

8. Reaction of Haloarenes:

X→ AgNO3 HNO3 Y Yellow or white ppt. Which of the following cannot be X?

Important Questions on Haloalkanes and Haloarenes