Amines and nucelophiles and their synethesis

Amines

Base properties of amines

Nucleophilic substition

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  • Created by: mariam
  • Created on: 14-11-10 23:50

Amine

Amine - derivative of amino acid which 1 or more of the hydrogens in the molecule has been replaced with ALKYL or ARYL groups

 

 

 

 

 

1' Amine                               2' Amine                          3' Amine

  • Alkyl - methyl amine, ethyl amine
  • Aryl - NH2 directly to the benzene ring 
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Physical properties and Solubility

Physical properties

  • Higher boiling point due to hydrogen bonding
  • As the carbon chain gets longer--> increased van der waals forces--> higher bp

 

Solubility

  • lower mass compunds soluble in water due to the H bonding with solvent
  • Solvent decreases as the molecules gets heavier
  • Soluble in Organic solvents
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Base properties of amines

Amines can accept a H+-----> BRONSTED LOWRY BASES

 

 

 

RNH2 + H+ -------> RNH3+ PROTON ACCEPTOR

INDUCTIVE- gives electron density (pushes it onto the N atom)

ELECTRON WITHDRAWING - Takes electron density (pulls electron density away from N atom)

Strength - greater the electron density on N the better it can pick up an proton.

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BAD base

 

 

  • Electron withdrawing substituents (benzene rings)---> decreases basicity as the electron density on N is decreased and the lone pair is less effective

 

GOOD base (INDUCTIVE EFFECT)

 

 

  • Electron releasing substituents (CH3 groups) increases basicity as the electron density is increased and the lone pair is more effective.
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Amines as nucleophiles

NUCLEOPHILIC SUBSTITUTION - Due to their lone pair

 

 

 

NH3      +    Rx --------> [RHN3]+   +   X-

[RNH3]  +     NH3 -------> RN2       +  [NH4]

Reagent - Haloalkane

Product - substitued amines

Ammonia is a nucleophile, when ammonia reacts with a haloalkane a primary amine is produced

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Amines - nucleophiles- attack haloalkanes to produce 2' amines----. this is a nucleophile too and can react further to produce 3' amine -----> ionice Quatenary salt 4' amine

 

  • C2H5NH2 + C2H5Br ----->  HBr + (C2H5)2 NH   DIETHYLAMINE 2'amine
  • (C2H5)2 NH + C2H5Br --------> HBr + (C2H5)3 N      TRIETHYLAMINE 3'amine
  • (C2H5)3 N   + C2H5Br --------> (C2H5)4 NA+Br-  TETRAETHYLAMMONIUM BROMIDE 4' amine

Creating Amines this way is not useful when a specific product is needed

Synthetic route produces 1',2',3',4' which is then separated by fractional distillation

 

BUT a larger excess of ammonium------> greater % of 1' amines produced.

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Why use excess ammonia?

Primary amines can be prepared from nitriles and haloalkane in a 2 step process

Step1                                                                                                                                                                                           Haloalkanes react with the cyanide ion in aqeous ethanol a NUCLEOPHILIC REACTION occurs

  • RBr + CN-  ------------> R - C=N  + Br-
  • 

Step2                                                                                                                                                                                                        Nitrile produc t can be reduced using catalytic hydrogenation (nickel and hydrogen)

  • R - C =N + 2H2 -------------> R-CH2NH2

Purer product arises as 1' amine can only be formed

Increasing the chain length ---------> Stronger base

Adding Benzene rings ----------------> weaker base

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Chemical Reactions

Step2                                                                                                                                                                                                        Nitrile produc t can be reduced using catalytic hydrogenation (nickel and hydrogen)

  

  • R - C =N + 2H2 -------------> R-CH2NH2

Purer product arises as 1' amine can only be formed

Increasing the chain length ---------> Stronger base

Adding Benzene rings ----------------> weaker base

Water - Amine dissolves in water produces weak alkaline solutions

CH3NH2(g)    +     H2O(l)     <---------->   CH3NH3+ (aq)    +    OH-(aq)

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Reaction as bases

Acid and amines react with acids ----------> produces salts

C6H5NH2   +   H+    +    Cl-    ---------------> C6H5NH3  +  Cl-

                                                                         Soluble       Phenylammonium chloride

- phenyl- amine is insoluble but it will dissolve in excess HCl as it forms the soluble ionic salt

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C6H5NH3+     +      Cl-     +     NaOH --------> C6H5NH2 + NaCl  + H20

                                                                     Insoluble amine and it forms a layer

If a strong base like NaOH is added it removes the H+ from the salt and makes the insoluble amine

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Making Phenyl amine from Benzene

Step 1

Benzene is reacted with a mixture of conc HNO2  +   H2SO4 -------> NITROBENZENE

Step 2

Nitrobenzene is reduced to Phenylamine using tin and Hcl as a reducing agent. They remove the oxygen atoms of the NO2 groups replacing them with hyderogen atoms

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