6.2.1 Amines, Amides, Amino Acids Flashcards
Amines from Halogenoalkanes
Reagents: excess, ammonia in ethanol
Conditions: reflux in excess, alcoholic solution under pressure.
Nucleophiles: ammonia (NH3)
Why excess?
Ensures that all the halogenoalkane molecules react with the ammonia before having the chance to react with any amines produced.
Prevents further substitution to secondary and tertiary amines.
Ethanol prevents water reacting with haloalkane to form alcohol.
Amines from Nitriles
Nitriles reduced with a reducing agent: LiAlH4 dissolved in ethoxyethane.
(the length of the hydrocarbon chain has increased)
Formation of aromatic amines
Phenylamine formed by reduction of nitrobenzene.
Reagents: Sn and conc. HCl
Conditions: reflux + NaOH(aq)
Separated from the mixture by:
Steam distilling (produce distillate containing phenylamine + water)
Separating funnel to obtain the immiscible phenylamine.
Drying to remove traces of water.
Redistilling to produce pure phenylamine.
Basicity of Amines
Have a lone pair of electrons on the nitrogen atom - allow amines to accept a proton by means of a coordinate bond.
Alkylamines are stronger bases because the alkyl groups ‘push’ electrons more onto the nitrogen atom making it more delta-.
Phenylamine is a much weaker bade as the lone pair on the nitrogen becomes part of the delocalised pi-electron system of the benzene ring (resonance effect)
Boiling Temp
Boiling temp of amines increase as the chain length increases.
More London forces between the molecules.
BP of the secondary amine is lower than its corresponding primary amine- less surface contact between the molecules.
Amines have higher BP than alkanes - amines can form Hydrogen bonds as well as London forces which require more energy to overcome.
But amines have lower BP than alcohols as nitrogen is less electronegative than oxygen.
Solubility in water
All amines form hydrogen bonds in water so, they are very soluble in water.
Solubility decreases as the hydrocarbon chain increases - hydrocarbon chains break more H bonds between water molecules than are reformed between water and NH2.
Ethanoylation
Amines act as nucleophiles due to the lone pair of electrons on the N.
They attack the Cdelta+ atom of the carbonyl group in ethanoyl chloride to form an amide - N-methylethanamide
Reagent: Ethanoyl chloride
Reaction with nitic(III) acid HNO2
Aliphatic amines react with nitrous acid so bubbles of colourless N2 gas is seen.
With NaNO2 + HCl(aq) :
If temp is between 0-10*C, a solution containing benzenediazonium chloride is formed.
With HCl(aq) + NaNO2
Benzenediazonium sulfate is formed.
Using cold nitric(III) acid can be used as a test to distinguish between aliphatic and aromatic amines:
If the temperature is above 10˚C, decomposition of the benzenediazonium ion occurs giving phenol and nitrogen.
Benzenediazonium salts
Bezenediazonium compounds ae extremely reactive +below 10*C, react with phenols + aromatic amines in alkaline solution.
Compounds formed contain N=N azo group - links the two benzene rings together.
Diazonium ion is a weak electrophile, needs high ED to attack.
Presence of an -OH or -NH2 group bonded to the ring increases ED (activation) - enables diazonium ion to bond via electrophilic substitution.
- Coupling, resulting compound - azo dye.
Amino acids
Contain an amine group+ carboxylic acid group bonded to same carbon atom.
General formula - RCH(NH2)COOH
All amino acids (except glycine) exhibit optical isomerism - chiral carbon
Reactions of a-amino acids with acids/bases
-NH2 group react with acids > accept H+ form ammonium ion (NH3+)
-COOH group react with bases > remove H+ form carboxylate ion (COO-)
e.g. valine + H+
(CH3)2CH(NH2)COOH + H+ > (CH3)2CH(NH3+)COOH
Reactions of amino acids with alcohol
Alcohol + conc H2SO4 +heat
>ester + water
alanine + ethanol + H+ >
Amides
Derivative of carboxylic acid where hydroxyl group has been replaced with ammonia/amine.
Typically prepared by reacting acyl chlorides with ammonia/amines + acid anhydrides.
