Haloalkanes and Haloarenes

Chemical Reactions

  • Chemical properties of haloalkanes:
    (a) Nucleophilic substitution reactions:

  • (*) On reacting with KOH(aq) ; Conc. KCN, RONa and NaNH2, 3° R-X gives alkene as the main product.
  • Reduction: (i) RX\xrightarrow[(or)Zn/HCl\ (or)\ Zn-Cu/C_{2}H_{5}OH]{{H_{2}/Ni(or) HI/Red\ P\ (or)\ TPH}}RH+HX
         TPH is triphenyl tin hydride
         (ii) LiAlH4 converts 3° Rx to alkene while NaBH4 does not react with iRX.
  • Some chemical properties of Haloarenes:
    (A) Electrophilic substitutions (SE) in benzene ring: Halogens are electron with drawing but active benzene ring for O/P electrophilic substitution through +M effect.
  • Trick for SE reaction:
  • Nucleophilic substitution reactions (SN): The reactivity of haloarenes is much less than haloalkanes because of partial double bond C = Cl Character, sp2-hybridisation of C-atoms of benzene, low polarity of C-Cl bond.
  • Addition-elimination reactions:
  • (a) 2C_{6}H_{5}Cl+2NH_{3}+Cu_{2}O\xrightarrow[]{{475K/60\ atm}}2C_{6}H_{5}-NH_{2}+2CuCl+H_{2}O
    (b) C_{6}H_{5}-Br+CuCN\xrightarrow[]{{475K/P_{4}}}C_{6}H_{5}CN+CuBr
  • * 2,4,6 Trinitro chlorobenzene reacts with hot water to produce picric acid.
  • Reactions with metals:
  • Benzyl chloride (C6H5CH2Cl)
    (i) It is phenyl substituted chloromethane. It can be prepared by using methods similar to chloro methane (or) chloro ethane.
    (ii) It gives the properties of substitution of Cl as CH3-CH2Cl, substitution of H of CH2 part as soluble and SE in benzene ring at ortho and para positions.
  • (iii) Substitution of Cl is similar to RCl but it is SN1 mechanism because is very stable.

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Part2: View the Topic in this Video from 1:25 to 58:28

Part3: View the Topic in this Video from 0:50 to 38:22

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