4.6 - Amines

Formation of primary aliphatic amines from halogenoalkanes

Heat in a sealed tube with excess ammonia in water/ethanol

Usual product is amine salt

Treatment of amine salt with alkali will release the amine

Formation of a secondary amine from halogenoalkanes

Excess of halogenoalkane so further substituion can occur

Equation for formation of primary aliphatic amines from halogenoalkanes

RCH₂X + NH₃ —> RCH₂NH₂ + HX

Formation of a primary aliphatic amine from a nitrile

LiAlH4 in ethoxyethane/ether

Equation for formation of a primary aliphatic amine from a nitrile

RCH2C≡N + 4[H] —> RCH2NH2

Formation of aromatic amines

Reduction of nitrobenzene

Metallic tin in conc HCl

Heat under reflux in a water bath

Phenylammonium formed

Cool + add aqueous NaOH

Explain how amines can act as a base

Contain a nitrogen atom/basic NH2 group that has a lone pair of electrons which can accept a proton through a coordinate bond

Are alkylamines weaker or stronger bases than ammonia?

Stronger

Explain why alkylamines are stronger bases than ammonia

The alkyl groups push electron towards the nitrogen atom, making it more electron-rich than the nitrogen in ammonia

Is phenylamine a weaker or stronger base than alkylamines?

Much weaker as the lone pair of electrons becomes integrated in the delocalised pi system

Product formed when amines react with acids

Amine salts

Equation for formation of an aromatic amine

Reagents and conditions for haloalkane —> amine

Sealed tube

Heat

Ammonia in water or ethanol

Reagents and conditions for nitrile —> anime

LiAlH4 in ethoxyethane/ether

Reagents and conditions for formation of an aromatic amine

Nitrobenzene

Sn/conc. HCl

Heat under reflux

2 reactions of amines

1. Ethanoylation using ethanoyl chloride

2. Cold nitric (III) acid

Equation for ethanoylation of primary amines

R-NH2 + CH3COCl —> R-NHCOCH3 + HCl

Explain the reaction of amines with ethanoyl chloride

The nitrogen lone pair enables an amine to react as a nucleophike. Attacks the highly electropositive carbon atom of the carbonyl group in ethanoyl chloride to form an amide

Product formed from ethanoylation of an amine

N-(r group on anime)ethanamide

Product formed from ethanoylation of an aromatic amide

N-phenylethanamide

Naming the product of ethanoylation of an amine

N-(R group of amine)ethanamide

N means R group is bonded to the nitrogen atom

Production of nitric (III) acid

Unstable compound made when required by reactions of a dilute acid and sodium nitrate (III) NaNO2

Formula of nitric(III) acid

HNO2

Alternative name for nitric(III) acid

HNO2

Reagents and conditions for reaction of amine with nitric(III) acid

HNO2

Room temp

Equation for reaction of primary aliphatic amine with nitric(III) acid

R-NH2 + HNO2 —> R-OH + N2(g) + H2O

Observations for reaction of amine with nitric(III) acid

Nitrogen gas produced so bubbles/effervescence

Product formed in reaction of primary aromatic amine with nitric(III) acid

Phenol and nitrogen gas

Product formed from reaction of primary aliphatic amine with nitric(III) acid

Alcohol and nitrogen gas

Product formed from reaction of primary aromatic amine with nitric(III) below 10•C

Stable benzenediazonium compound ion is formed

Product of reaction of phenol/aromatic amines and benzenediazonium compounds

Compounds where the -N≡N- azo group is retained (azo dyes)

Reagents and conditions for reaction of phenol benzenediazonium compounds

Below 10•C

Alkaline solution

Azo linkage

-N≡N-

Position of coupling reactions

4-position relative to the -OH or -NH2 group

Colours of azo dyes

Yellow, orange or red

Production of azo dyes

Phenol or aromatic amine + benzenediazonium compounds

Colour of Naphthalen-2-ol

Red azo dye

Solution necessary for coupling to occur

Alkaline

Role of the -N≡N- group in an azo dye

A chromophore

Chromophore

A group that absorbs colour in the visible and UV region. The wavelength of light dictates the colour we see. Colour seen is the one complementary to the one absorbed

Explain the origin of colour in azo dyes

• Chromophore absorbs light

• Wavelength of light absorbed dictates the complementary colour seen

• Colour seen is complementary to the one seen

• e.g. blue-green is absorbed so red is seen