Chemistry: Alcohols, Phenols and Ether

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


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



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 :