Compounds Containing Halogens is one of those topics which can fetch you lot of marks very easily. So, go through these important notes of Compounds Containing Halogens to score your best.
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.
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Methods of Preparation of Alkyl Halides:
(a)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
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:
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Reactions of Alkyl Halides: Hydrolysis: : RX + OH– → ROH + X–
Williamson Synthasis: R-ONa +R’X → R-R’ + NaX
Reaction with dry silver oxide: 2R-X + Ag2O → R-O-R
Reaction with sodio-Alkynides: R-C≡C-Na +X-R→ R-C=C-R +NaX
Reaction with potassium-cyanide: KCN+X-R→ RCN +KX
Reaction with silver-cyanide: AgCN+X-R→ RNC +AgX
Reaction with silver-nitrite: AgNO2+X-R→ RNO2 +AgX
Reaction with potassium-nitrite: KNO2+X-R→ R-O-N=O +KX Fridal
Craft Reaction: R-X + C6H6 + AlCl3→C6H5-R
Malonic Ester Synthasis: R-X + -CH(CO2C2H5)2 →R-CH(CO2C2H5)2 +HX
Acetoacetic Ester Synthasis: R-X + -CH(CO2CH3)2 →R-CH(CO2CH3)2 +HX
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Reaction with Ammonia: R-X +NH3→ R-NH2 +HX
Wurtz Reaction: 2R-I+ 2Na →R—R + 2NaI
Dehydrohalogenation: CH3.CH2.CH2Br + alco.KOH → CH3–CH = CH2 + KBr + H2O
Reaction with alcoholic AgNO3: R-X +AgNO3 → R+ + AgX↓+HNO3
Substitution Versus Elimination
Preparation: It can be prepared from any alcohol having –CH(OH)CH3 group or from the aldehydes and ketones formed from above type of alcohols i.e, from a carbonyl compound having three a – hydrogen atoms by the action of X2 and an alkali or Na2CO3.
Laboratory Preparation of CHCl3
Physical properties of CHCl3: colourless liquid with sweet smell and test. It is heavier than water and insoluble in it but soluble in alcohol and ether.
Chemical Reactions of CHCl3:
- Oxidation: CHCl3 + 1/2 O2 → HCl + COCl2 (phosgene)
- Hydrolysis: CHCl3 + 4NaOH → HCOONa + 3NaCl + 2H2O Carbyl
- amine reactions: CHCl3 + CH3NH2 + 3NaOH →CH3N≡C +3NaCl +3H2O
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