Haloalkanes and haloarenes - 1 Flashcards
X2/hv ( Halogenation in presence of sunlight)
1) Alkanes to Alkyl halide
2) Halogenation
3) X replaces H
4) FRSR
The reaction of ROH with HX
1) Formation of alkyl halide
2) HX bond breaks and forms H+ and X-
3) Protonation ( Addition of H+)
4) Removal of water
5) Rearrangement if possible
Why rearrangement is required in some reactions?
To attain stability
Types of rearrangements?
1) Hydride shift
2) Methyl shift
3) Ring expansion ( + Outside the ring)
4) Ring Contraction( + On the ring)
Ring expansion can’t happen in
3 and 6 bcz of dancing reso and ring stability respectively.
We can also use reagent like_______ in the reaction of ROH with conc. HX
NaBr + H2SO4
For 1* and 2* Alcohol, Catalyst is
Required
For 3* Alcohol, Catalyst is
NOT REQUIRED as carbonium ion is more stable.
ROR of ROH
3> 2>1*
ROR of HX
HI>HBR>HCL
Explain the preparation of RCl
Either by Passing dry HCl gas through a solution of alcohol or by heating solution of alcohol in conc. aq acid.
Preparation of RBr
Constant boiling with HBr(48%) is used for the preparation of RBr
Preparation of RI
Good yield may be obtained by heating ROH with NaI or KI in H3PO4 (94%)
Why is sulphuric acid is not used during the alcohols with KI or NaI
H2SO4 is a strong oxidising agent and it oxidizes HI formed during the reaction to I2 which doesn’t react with alcohol.
Luca’s reagent test
Conc. HCl +anyd. ZnCl2, to distinguish between 1, 2 and 3* Alcohol.
ROH in presence of conc. Hcl gives RCl
