Amines

Question 1

Methods of preparation for amine ? (Total6)

Answer 1

(1.) Reduction of NO2 compounds

  Reduction of aliphatic/aromatic NO2 compounds using :
  a. H2 in presence of Ni/Pt/Pd and C2H5OH
  b. Sn + HCl(conc.) OR Fe + HCl(conc.) {With metals in acidic
  medium}

  >Reduction with Fe+HCl is preferred cz FeCl2 formed gets
   hydrolyzed to release HCl

(2.) Ammonolysis of alky halides

 Cleavage of R-X bond by NH3 molecule 

 • The process continues to form primary, secondary, tertiary
    amines followed by formation of quaternary ammonium
    salt  nd rxn terminates .
 
  Free amine can be obtained from ammonium salt + NaOH
  (strong base) 
  RNH2X + NaOH ➡️ RNH2 + H2O + NaX

(3.) Reduction with nitriles (aromatic/aliphatic)

  RCN on reduction with LiAlH4 OR H2 in presence of Ni/ Pd/
   Pt  OR H2 + Na(Hg) with C2H5OH gives RNH2

(4.) Reduction of amides

   R-C=ONH2 on reduction with LiAlH4 followed by hydrolysis
   gives R-CH2-NH2

IMPORTANT NAME RXN

(5.) Gabriel phthalamide synthesis

  Phthalamide reacts with KOH (K replaces H ) product formed reacts with RX (K replaces by R) forming  N-Alkylphthalamide reacts with H+/OH-  product formed reacts with 2NaOH (aq) to give RNH2 and byproduct .

(6.) Hoffmann bromamide degradation rxn

  Amide reacts with Br2 + 4NaOH to give RNH2 + Na2CO3 + 2NaBr + 2H2O

Question 2

Physical properties (total 4)

Answer 2

(1.)Boiling point:
H bonding is responsible for bp of amines
primary > secondary > tertiary

(2.)The first two members are combustible gases
C3-C11 are liquid
C12 to further are solids

(3.)Pure amines are colourless but show colour when oxidised due to atmospheric conditions

(4.)ROH are more polar than RNH2 due to stonger intermolecular H bonding

Question 3

About basicity of amines.

Answer 3

Amines are reactive bcz of electronegativity difference b/w N and H and due to presence of lone pair.

Amines have a lone pair available for sharing and thus acts as lewis base.

Aromatic amines are weaker bases as aryl group acts as EWG

Aliphatic amines are stronger bases due to presence of R group showing +I effect thus inc. e- density on N

More stable the cation is the more basic the amine .

Question 4

Relation b/w amines and kb, pkb and kc values?

Answer 4

Basicity directly proportional to kb

Basicity inversely proportional to pkb

Baisicity directly proportional to kc

Question 5

What is the Ortho effect?

Answer 5

Exceptionally ortho substituted anilines are weaker bases than para substituted aniline, meta substituted aniline and aniline due to electronic repulsion and steric hinderence k/a ortho effect.

Question 6

Baisicity of RNH2 in gaseous phase? Alakamine v/s ammonia

Answer 6

Depends on the +I effect (directly proportional) i.e more the R groups present more is the basicity

Order of basicity (dec. order) 3°>2°>1°

RNH2 is more basic than NH3 due to presence of R group in RNH2 .