• The nitrogen atom in ammonia and amine molecules can?accept?a?proton?(H+?ion)
• They can therefore act as?bases?in aqueous solutions by?donating?its lone pair of electrons to a proton and form a?dative bond
  • For example, ammonia undergoes an?acid-base?reaction with dilute hydrochloric acid (HCl) to form a salt

   

NH3?+ HCl?→ NH4+Cl-

base????? acid??????????? salt

• Amines react with HCl?to form amine salts, such as ethylammonium chloride

C2H5NH2?+ HCl?→ C2H5NH3+Cl-

base? ? ? ? ? acid? ? ? ? ? ? ? ? ?salt

• Like ammonium salts, amine salts are soluble ionic compounds, so when the alkyl group is small they are water soluble but become less so as the carbon chain increases
• We can show the reaction in?Br?nsted-Lowry terms, where ammonia or the amine acts as a?proton acceptor:

The nitrogen atom in ammonia and amines can donate its lone pair of electrons to form a bond with a proton and therefore act as a base

?Strength of ammonia and amines as bases

• The?strength?of amines depends on the?ability?of the lone pair of electrons on the nitrogen atom to accept a proton and form a dative covalent bond
• The?more readily?a proton is attracted, the?stronger the base?is
• Factors that may affect the?basicity?of amines include:
  • Positive inductive effect?- Some groups such as?alkyl groups?donate electron density to the nitrogen atom causing the lone pair of electrons to become more available and therefore?increasing?the amine’s?basicity
  • Delocalisation?- The presence of aromatic rings such as the?benzene ring?causes the lone pair of electrons on the nitrogen atom to be?delocalised?into the benzene ring
  • The lone pair becomes?less available?to form a dative covalent bond with ammonia and hence?decreases?the amine’s?basicity

   

• For example, ethylamine (which has an electron-donating ethyl group) is?more basic?than?phenylamine?(which has an electron-withdrawing benzene ring)

Ethylamine is more basic than phenylamine due to electron donating ethyl group which increases electron density on the nitrogen and makes it more attractive to protons