4. reactions of amines

• nucleophile 


  lone pair donor
• what can be donated to an electropositive d+ carbon atom?

  the long pair of electrons on the nitrogen atom
• nucleophilic substitution to create amines

  
• This is not a good way to prepare propylamine. Why? What do you think might happen next?


  The primary amine produced has a lone pair of electrons on the nitrogen atom and can itself behave as a nucleophile. ​

  ​

  It will react with any unused 1-bromopropane. 
• CH3CH2CH2Br + 2NH3 → CH3CH2CH2NH2 + NH4Br


  CH3CH2CH2NH2 has a lone pair so can react with CH3CH2CH2Br - results in a successive substitution occurring and the formation of a secondary amine
• successive reactions 


  CH3CH2CH2NH2 + CH3CH2CH2Br → (CH3CH2CH2)2NH + HBr

  (CH3CH2CH2)2NH + CH3CH2CH2Br → (CH3CH2CH2)3N + HBr

  (CH3CH2CH2)3N + CH3CH2CH2Br → (CH3CH2CH2)4NBr​
• What conditions would be required to produce a quaternary ammonium salt?

  Excess halogenoalkane.
• What conditions would be required to just stay with a primary amine as the main product?

  Excess ammonia
• quaternary ammonium salts 


  e.g. Cationic surfactants in fabric conditioners and hair products

  • coat the surface of the cloth or hair with positive charges and reduce the static due to negatively charged electrons.​
• acetylcholine chloride 


  naturally occurring quaternary ammonium compound

  
• acetylcholine

  • When a voluntary nerve cell is stimulated acetylcholine is released at the nerve endings. 
  • After it has been active in  transmitting a nerve impulse, acetylcholine is removed.
  • Only in the presence of the specific enzyme (acetylcholinesterase) does the reaction take place rapidly. 
• VX gas

  • tertiary amine which inhibits the enzyme acetylchloinesterase.
  • Early symptoms of percutaneous exposure (skin contact) may be local muscular twitching or sweating at the area of exposure followed by nausea or vomiting.

  
• reaction of primary amines

  Primary amines react with acyl chlorides and acid anhydrides to form N-substituted amides.
• Write an equation for the reaction of methylamine with ethanoyl chloride and name the products formed. Outline the mechanism.

  • CH3NH2 + CH3COCl → CH3CONHCH3 + HCl 
  • N-methylethanamide

  
• nucleophilic substitution 


  amines can be prepared by nucleophilic substitution of halogenoalkanes
• NS is not a good way of preparing a primary amine. Why?

  The amine produced has a lone pair of electrons on the nitrogen atom and can itself behave as a nucleophile attacking any unreacted halogenoalkane. 
• reduction 


  Amines can be formed by the reduction of nitriles using hydrogen in the presence of a nickel catalyst or LiAlH4 in dry ether, usually represented by [H].
• Write an equation to show the reduction with hydrogen of ethanenitrile to form ethylamine.

  CH3CN + 2H2 → CH3CH2NH2
• If you use LiAlH4 as the reducing agent the equation is written as follows.

  CH3CN + 4[H] → CH3CH2NH2
• Aromatic amines are prepared by the reduction of nitro compounds.


  also achieved using hydrogen and a nickel catalyst or in the presence of Sn or Fe with HCl, usually represented by [H], followed by addition of NaOH.
• Write an equation to show the reduction of nitrobenzene to form phenylamine.

  
• multi-step conversion

  
• answer of multi-step conversion

  
• nucleophilic addition-elimination


  Primary amine with and acid anhydride to produce the N-substituted amide

  N-phenyl ethanamide

  
• uses of amines

  • Methyl orange is a pH indicator frequently used in titrations because of its clear and distinct colour change. ​
  • This is an example of an azo-dye and is made from aromatic amines.