Nitrogen Compounds• Aims:• To know that these include amines, amides, nitro

compounds, nitriles and amino acids.• To know that amines are derivatives of ammonia.• To know that they are categorised as primary,

secondary and tertiary amines by the number of substituents (R- groups) on the nitrogen atom.

• To know that amines, like ammonia are BASES.• To explain the basicity of amines in terms of

proton acceptance by the nitrogen lone pair.• To describe the reactions of amines with acids to

form salts.

Nitrogen Compounds

• Amines are organic derivatives of ammonia.

• Ammonia is NH3.

• If H atoms are replaced by alkyl chains then the compound formed is an amine.

NH3 ammonia

C2H5NH2 ethylamine Primary amine

(C2H5)2NH diethylamine

Secondary amine

(C2H5)3N triethylamine Tertiary amine

Name some amines

• (CH3)2NH Draw phenylamine.

• CH3(C3H7)NH Draw N,Ndimethylethylamine

• C2H5(C3H7)NH

• (CH3)3N

• Predict the shape of amines and explain it.

Properties of Amines

• Amines are described as having a fishy smell (because when fish start to go off they produce amines as decomposition products such as putrescine NH2(CH)4NH2 and cadaverine NH2(CH2)5NH2.)

• Short chain amines are gaseous and very soluble in water. Why? Why are the mp and bp less than similar RMM alcohols?

• Melting points and boiling points increase with increasing chain length. Why?

• Solubility in water decreases with increasing chain length. Why?

Reactivity of Amines

• Amines are BASES.• Basicity depends on substituents on

the amine chain.Amine pH 1 mol.dm-3

soln% molecules reacted in solution.

ammonia 11.63 0.42

methylamine 12.32 2.08

ethylamine 12.35 2.25

phenylamine 9.32 2.08 x 10-3

Week 6

© Pearson Education Ltd 2009This document may have been altered from the original

Reaction of methylamine as a base

Amines as Alkalis

• When an amine dissolves in water the nitrogen accepts a proton from the water producing an ammonium ion or a substituted ammonium ion.

• The presence of OH- ions in the solution means that the solution is alkaline.

• The reactions are equilibrium reactions and so ammonia and amines are weak bases.

• NH3 + H2O NH4+ + OH-

Reactions With Acids

• In the reaction with acids the salts formed are ionic compounds and so will dissolve in the aqueous solution.

• The smell of the amine also disappears.• If the water is evaporated a white crystalline solid

salt will form.• Even though phenylamine is a much weaker base

and less soluble (why?) than aliphatic amines, it too will react with acids to form soluble salts.

• If a strong base, like sodium hydroxide is added it removes a proton from the salt and regenerates the insoluble amine.