Amines Flashcards
How many total isomers does C4H11N have? How many structural isomers?
It has a total of 9 isomers. Only 8 structural isomers becuase one is optically active hence there are d and l forms.
Benzene with Nh2 and Ch3
o-Toludine
Benzene with NH2 and OCH3
m-Anisidine
C6H6CH2NH2
Benzylamine
Structure of amines
NItrogen has sp3 hybridised orbitals, 3 sigma bonds, one lone pair, bond angle is 107 in 1 and 2 amines due to lp-bp repulsion but in 3 amines it is 108 due to repulsion between alkyl groups.
Preparation of amines by reduction of nitro compounds
Yields primary aliphatic and aromatic amines
General reaction- R-NO2+6H–R-NH2+2H20
REAGENTS USED;
1. Catalytic reduction using H2/Ni, H2/Pd/Pt
2. Using active metals like Fe/Hcl or sn/Hcl
3. Using LiAlH4- gives aliphatic primary amine but azobenzene when treated with nitrobenzene.
Why is reduction using iron scrap and HCL preferred
FeCl2 formed gets hydrolysed to produce Hcl thus only a small amount of Hcl is required to initiate the reaction.
Hoffman’s ammonolysis
See notes for mechanism.
Reduction of cyanides
Gives primary amines
Reagents;
1. H2/ Raney Ni
2. LiAlH4
3. Na/alcohol (Mendiv’s reduction)
4. Na-Hg/alcohol
Reduction of isocyanides
Gives N methyl secondary amines
Hydrolysis of isocyanides
Gives primary amine+ fomic acid
Hydrolysis of nitriles
Gives RCOOH+ NH3
Reduction of amides
Requires a strong reducing agent like LiAlH4. Gives primary, secondary or 3 amines depending on the type of amide used.
Gabriel phthalimide reaction
Gives primary amine. See mechanism.
Hoffman Bromamide Reaction
RCONH2+BR2=4NAOH GIVES RNH2+ NA2CO3+ 2NABR+ 2H2O
Methylamine and ethylamine are
Gases
Aryl amines are usually
colourless but get colored due to oxidation when stored
Boiling point of isomeric amines
1>2>3
solubility of amines
As size of alkyl part increases, they become less soluble so that is why higher members are not soluble.
Larger the value of Kb or smaller the value of pKb
Stronger is the base.
What happens to basicity when there are electron donating groups
Increases
What happens to basicity when electron withdrawing groups are present?
decreases
Order of basicity in pure state
3>2>1> NH3
Which is more basic Ammonia or Alkyl amine
Alkyl amine due to +I effect
in aqueous soln, if alkyl group is methyl, then order of basicity is
2>1>3
In aqueous soln, if alkyl group is not methyl then order of basicity is
2>3>1
Why are Anilines not basic?
Lone pairs are not available since they are involved in resonance. Also anilinium ion formed has only 2 resonating structures, hence it is less stable than Aniline.
Acylation of amines
R-NH2+ RCOG GIVES R-NH-CO R. Study mechanism. Remember to use Pyridine in case of aromatic amines.
Use of acylation
Since the lone pairs on nitrogen are involved in resonance with CO bond, the basicity gets reduced.
What kind of amines do not undergo acylation
tertiary
Carbylamine test
Aliphatic and aromatic primary amines react with chloroform in the presence of KOH to give isocyanide, KCl and water. It is a distinguishing test for primary amines.
I
Intermediate in carbylamine test
Dichloro carbene
Reaction of primary aromatic amines with nitrous acid
Produces Diazonium salt, NaX and water. Takes place in low temperatures like 273-278 K.
How does primary aliphatic amines react with Nitrous acid
They produce unstable diazonium salts which liberate nitrogen and alcohol.
