Topic 12 - Compounds Containing Nitrogen Flashcards
How can aliphatic amines be produced?
The action of ammonia on a halogeno alkane
Reductions of nitriles by lithium-tetrahydrido-AluminateIII
Reductions of amides by lithium-tetrahydrido-AluminateIII
What are amines?
Amines are organic derivatives of ammonia. If one alkyl group replaces one of the hydrogen atoms of ammonia a primary aliphatic amine is formed.
E.g CH₃NH₂ which is called methylamine or aminomethane.
If an aliphatic ring replaces one of ammonia’s hydrogen atoms a primary aromatic amine results.
Outline the production of an amine from a halogeno alkane.
Aliphatic amines are prepared by the action of ammonia on a halogeno alkane the two reactants are dissolved in ethanol and then heated together in a bomb (a metal container which will withstand high pressure). To extract the free amine an alkali is added and then fractional distillation is used.
What must be considered when nitriles and amides are reduced to produce amines?
The reducing agent must not be acidic as to would cause hydrolysis of the nitrile
How are aromatic amines produced?
Aromatic amines must be prepared from nitro compounds
e.g phenylamine which is made from nitrobenzene using tin(Sn) and concentrated HCl as the reducing agent. the mixture is refluxed for about 30 minutes and then NaOH is added to release the aniline which is extracted by steam distillation. A mixture of water and aniline collects and ether is used to extract the aniline The ether is distiller off and the aniline further purified by boiling under reduced pressure. It decomposes at its normal boiling point.
Outline the physical properties of aliphatic amines?
Hydrogen bonding is present but nitrogen is less electronegative than oxygen so the intermolecular bonds are weaker and the lower(shorter carbon chains) amines are gasses and will dissolve in water as they will form hydrogen bonds with it. They have a characteristic smell which is describes as fishy. They are formed when proteins decay.
Outline the differences in physical properties of between aromatic and aliphatic amines.
Phenyl amine is insoluble in water but soluble in organic solvents as it is soluble in fatty tissues it can be absorbed through the skin.
What is more basic in nature; aqueous ammonia or an aromatic amine?
Aromatic amines are weaker bases. The electron pair on the Nitrogen atom is partially delocalised by interacting with π electron cloud of the benzene ring. This means that the lone pair is less available for coordinating to a proton.
How may the ethanoylation of An amino be acheived?
By reaction with ethanoyl chloride. These substituted amides are solids and so can be used to identify the original amine. Ethanoic anhydride reacts in the same way.
Why are amines basic in nature?
The Nitrogen atom in amine has a lone pair of electrons allowing combination with a proton so amines behave as proton acceptors I.e they are bases.
What happens when amines react with acids?
They form salts which are soluble in water.
E.g CH₂NH₂ + HCl → CH₃NH₃ + Cl⁻
What is more basic, an aliphatic amine or ammonia(aq)?
Aliphatic amines are stronger bases than ammonia in aqueous solution since the positive charge on the alkyl ammonium ion can be shared between the nitrogen atom and the carbon atom. This distribution of charge makes the cation more stable.
