Here are some important notes on Alcohol, phenol & ether for your CBSE examinations & IIT- JEE entrance. Make sure that you go through these notes to score the best.
Preparation of Alcohols:
- By hydrolysis of haloalkanes : R-X + aq. KOH →ROH +KX
- By reduction of Carbonyl compounds :
- By the action of Grignard’s Reagent on aldehydes, ketones and esters:
- By Aliphatic Primary Amines: RCH2NH2 + HNO2 → RCH2OH + N2 + H2O
- Hydration of alkenes:
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- Hydroxylation of alkenes:
Physical Properties of Alcohol:
- Lower alcohols are liquid at room temperature while higher ones are solid.
- High boiling point due to presence of intermolecular hydrogen bonding. Order of Boiling Point: primary > secondary > tertiary
- Solubility in water decreases with increase in molecular mass due to decrease in extent of intermolecular hydrogen bonding.
Chemical Properties of Alcohol:
- Alcohol’s reaction with metal: ROH + Na→2RO+Na– + H2
- Formation of Halides:
3ROH + P+I2→3RI + H3PO3
ROH + SOCl2/PCl3/PCl5→ RCl
ROH+ Zn+HCl→R-Cl R2C-OH alcohol + HCl→ R2CCl
- Reaction with HNO3: R-OH + HO-NO2→ R-O-NO2
- Reaction with carboxylic acid (Esterification) : R-OH +R’-COOH +H+↔ R’-COOR
- Reaction with Grignard reagent: R’OH + RMgX → RH + R’OMgX
- Reduction of alcohol : ROH + 2HI + Red P→ RH +I2+H2O
- Dehydration of Alcohol: Dehydration of alcohols takes place in acidic medium. Intramolecular dehydration leads to the formation of alkene while inter molecular dehydration which forms ether. Ease of dehydration: 3° > 2° > 1
- Satyzeff’s Rule : Elimination through b carbon containing minimum b hydrogen
- Oxidation of Alcohol:
RCH2-OH + [O] → RCHO → RCOOH
RCH2-OH + [O] +PCC → RCHO
- Haloform Reaction: Compound containing CH3CO- group (or compound on oxidation gives CH3CO – group) which is attached with a C or H, in presence of halogen and mild alkali gives haloform.CH3-CH2-COCH2-CH3, CH3-CO-Cl, CH3COOH will not respond to haloform reaction wile CH3CH2OH will respond to haloform Reaction.
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Test for Alcohols:
1. Lucas Test:
Alcohols + ZnCl2 + HCl
1o Alcohol: RCH2OH + ZnCl2 +HCl → No reaction at room temperature
20 Alcohol: R2CHOH + ZnCl2 +HCl → R2CHCl White turbidity after 5-10 min.
30 Alcohol: R3CHOH + ZnCl2 +HCl → R3CHCl white turbidity instantaneously.
2. Victor Meyer Test:
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Physical Properties of Phenols:
- Phenol is a colorless, toxic, corrosive, needle shaped solid.
- Phenol soon liquifies due to high hygroscopic nature.
- Phenol is less soluble in water, but readily soluble in organic solvents.
- Simplest phenols, because of hydrogen bonding have quite high boiling points.
- o-nitrophenol is, steam volatile and also is less soluble in water because of intramolecular hydrogen bonding
Chemical Properties of Phenols:
a) Formation of Esters
Phenyl esters (RCOOAr) are not formed directly from RCOOH. Instead, acid chlorides or anhydrides are reacted with ArOH in the presence of strong base
(CH3CO)2O + C6H5OH + NaOH → CH3COOC6H5 + CH3COONa + H2O
C6H5COCl + C6H5OH + NaOH → C6H5COOC6H5 + Na+Cl– + H2O
e) Electrophilic Substitution : The —OH and even more so the —O(phenoxide) are strongly activating ortho ,para – directing.
Special mild conditions are needed to achieve electrophilic monosubstituion in phenols because their high reactivity favors both polysubstitution and oxidation
Physical Properties of Ethers
Physical state, colour and odour: Dimethyl ether and ethyl methyl ether is gas at ordinary temperature while the other lower homologues of ethers are colourless liquid with characteristic ‘ether smell’.
Dipole nature: Ethers have a tetrahedral geometry i.e., oxygen is sp3 hybridized. The C— O—C angle in ethers is 110°. Because of the greater electronegativity of oxygen than carbon, the C—O bonds are slightly polar and are inclined to each other at an angle of 110°, resulting in a net dipole moment.
Bond angle of ether is greater than that of tetrahedral bond angle of 109°28′.
Solubility and boiling point: Due to the formation of less degree of hydrogen bonding, ethers have lower boiling point than their corresponding isomeric alcohols and are slightly soluble in water.
Preparation of Ethers:
a) From alcohols:
Order of dehydration of alcohol leading to formation of ethers: 1° > 2° > 3°
b) Williamson’s synthesis:
R-X + Na+ -O-R’ → R-O-R’ + Na+ X –
In case of tertiary substrate elimination occurs giving alkenes.
From Grignard reagent: Treating a – halo ethers with suitable Grignard reagents.
On standing in contact with air, most aliphatic ethers are converted slowly into unstable peroxides. The presence of peroxides is indicated by formation of a red colour when the ether is shaken with an aqueous solution of ferrous ammonium sulfate and potassium thiocyanate
i) Reaction with acid chlorides and anhydrides:
j) Electrophilic substitution reactions
Epoxides or Oxiranes:
a) Oxidation of ethylene :
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