CHE 101 Chapter Notes - Chapter 10: Thionyl Chloride, Zinc Chloride, Chlorobenzene

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3 Feb 2021
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Revision Notes on Organic Compounds Containing
Halogens
Organic Compounds Containing Halogens can be divided into two groups:
Alkyl Halides: Aliphatic carbon chain with halogen atom(s) as substitution.. Example:
Chlorobutane.
Aryl Halides: Aromatic carbon ring with halogen atom(s) as substitution on ring.
Example: Chlorobenzene.
Methods of Preparation of Alkyl Halides:
Grove’s process: Replacement of “OH” group in primary and secondary alcohols with an “X’ atom in
presence of Zinc chloride.
The reaction follows SN2 mechanism when the concentration of zinc chloride is low.
(b) Darzen Process: Reaction of thionyl chloride with straight-chain primary alcohols without
presence or absence of pyridine.
In presence of pyridine:
ROH + SOCl2 → HCl + ROSOCl
HCl+C5H5N →C5H5NH++Cl-
ROSOCl + Cl →RCl + SO2(SN2)
Action of a phosphorus halide on the alcohol: ROH + PCl5 → RCl + HCl + POCl3.
By addition of Halogen to an alefins: R-CH=CH2 +Br2+CCl4 →R-CH(Br)CH2Br
Photohalogenation: CH4 + Cl2 +hv CH3Cl + HCl
Displacement of one halogen atom by another:RCl + NaI →RI + NaCl
Bonodine – Hünsdiecker Reaction: RCO2Ag + Br2→RBr + CO2 + AgBr
Hydrohalogenation of unsaturated hydrocarbons:
In absence of peroxide: RCH=CH2 +HBr→RCH(Br)CH3
In presence of peroxide: RCH=CH2 +HBr + Peroxide →RCH2CH2Br
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Methods of Preparation of aryl halides
Halogenation: Ar-H + X2 +Lewis Base → Ar-x + HX
From diazonium salts:
C6H5N2Cl + HBF4 →C6H5F (Schiemann Reaction)
C6H5N2Cl + CuCl →C6H5Cl (Sandmeyer Reaction)
C6H5N2Cl + Cu powder →C6H5Cl (Gatterman Reaction)
SN1 and SN2 mechanism:
SN1
SN2
Steps
Two :
(1) R:Xl → R+ + X-
(2) R+ + Nu- l →RNu
One :
R:X + Nu- l → RNu + X-
Rate
=K [RX] (1st order)
=K[RX] [:Nu-] (2nd order)
TS of slow step
Stereochemistry
Inversion and racemization
Inversion (backside attack)
Molecularity
Unimolecular
Bimolecular
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