Alcohol, Phenol and Ether Short Revision Notes

 

Alcohols

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: 
     
• Oxymercuration-demercuration: 
  
• Hydroboration-oxidation:
  
• 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

• 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. Intra-molecular 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

• 1^o  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

Phenols:

Preparation: 

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

                                                 Phenyl acetate

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

                                                  Phenyl benzoate 

e) Electrophilic SubstitutionThe —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
 

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'.

• 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

Epoxides or Oxiranes:

Preparation

a)  Oxidation of ethylene : 

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