Important notes of Alcohol, phenol & ether for CBSE & IIT-JEE

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 :

 

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  • By the action of Grignard’s Reagent on aldehydes, ketones and esters:

  • By Aliphatic Primary Amines: RCH2NH2 + HNO2 → RCH2OH + N2 + H2O
  • Hydration of alkenes:

  • Oxymercuration-demercuration:

  • Hydroboration-oxidation:

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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+HX→ RX

ROH+ NaBr,H2SO4→R-Br

ROH+ Zn+HCl→R-Cl R2C-OH alcohol + HCl→ R2CCl

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  • 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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Phenols

Preparation:

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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

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Phenyl acetate

C6H5COCl + C6H5OH + NaOH → C6H5COOC6H5 + Na+Cl– + H2O

Phenyl benzoate

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

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Ethers

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’.

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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 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

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i) Reaction with acid chlorides and anhydrides:

j) Electrophilic substitution reactions

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Epoxides or Oxiranes:

Preparation

a) Oxidation of ethylene :

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