Amines Flashcards
Primary amine
The nitrogen atom is attached to one carbon chain
how are amines named if the -NH2 is on carbon 1
alkylamine
how are amines names if the -NH2 is on any carbon besides carbon 1
-aminoalkane
How do you name compounds where two or more different groups are attached to a nitrogen atom
N-substituted derivative of the larger group
Why do amines have a high boiling temperature
There are hydrogen bonds between molecules of an amine as they have a polar N-H bond
Why does ethylamine dissolve in water
It can form hydrogen bonds with water molecules because is has a polar N-H bond
Why are amines less soluble in water as the relative molecular mass increases
As the molar mass increases, the non-polar hydrocarbon chain which is insoluble becomes larger. Therefore solubility decreases
What are the two ways primary aliphatic amines are prepared
By the reaction of ammonia with halogenoalkanes and by the reduction of nitriles
What are the reagents, conditions and the mechanism for the reaction of ammonia with halogenoalkanes
Reagent - excess ammonia dissolved in ethanol
Conditions - Heat under pressure in a sealed tube
Mechanism - Nucleophilic substitution
Why is ammonia dissolved in ethanol when reacting with a halogenoalkane
To prevent halogenoalkane reacting with water as water is a nucleophile.
Alcohol is also formed
Why is excess ammonia used when reacting with a halogenoalkane
To prevent further substitution of the amine group to form secondary and tertiary amines
Reagents and conditions needed for the reduction of nitriles to amines
Reagents : H2/Ni
Conditions : High temperature, high pressure
What is the equation for the reduction of propanenitrile to propylamine
CH3CH2CN + 2H2 = CH3CH2CH2NH2
How are aromatic amines prepared
By the reduction of nitro compounds such as nitrobenzene
Reagents, conditions and reaction for nitrobenzene into phenylamine
Reagents: Sn/HCL
Conditions : Heat under reflux
Reaction : Reduction
What are aromatic amines used in
The preparation of dyes
What does ammonia act as in the first step of nucleophilic substitution
A nucleophile as it donates a lone pair of electrons
What does ammonia act as in the second step of nucleophilic substitution
A base as it reacts with a H+ ion to form an NH4+ ion
Equation for the reduction of nitrobenzene into phenylamine
C6H5NO2 + 6[H] = C6H5NH2 + 2H2O
Are amines basic or acidic
Amines are weak bases as the lone pair of electrons on the N atom allows an amine to act as a base
What is the order of base strength of amines
Aromatic amines < ammonia < primary amines < tertiary amines < Secondary amines
Why are primary aliphatic amines stronger bases than ammonia
The alkyl groups are electron releasing and push electrons towards the nitrogen atom, making the lone pair of electrons on the nitrogen more readily available. (CAN SAY POSITIVE INDUCTIVE EFFECT)
Why are secondary amines stronger bases than primary amines
Secondary amines have more alkyl groups therefore more electron density pushed onto the N atom and the positive inductive effect is greater. The lone pair of electrons on the N atom is more readily available.
Why are primary aromatic amines such as phenylamine such weak bases
The lone pair of electrons on the nitrogen delocalise into the benzene ring so the lone pair on the N atom is less readily available.
How do amines react with acids
They form ammonium salts
What happens if NaOH is added to an ammonium salt
Converts back to the amine
Why are ammonium salts soluble
They are ionic compounds
How are secondary amines formed
The primary amine reacts with the halogenoalkane as it has a lone pair of electrons on the nitrogen.
THIS TREND REPEATS TO FORM TERTIARY AMINES AND QUATERNARY SALTS (only first step of nuc subs happens when forming quaternary ammonium salts, they remain as carbocations)
For the formation of tertiary, the secondary reacts with halogenoalkane and makes a carbocation and then NH3 attacks carbocation
Uses of quaternary ammonium salts
cationic surfactants
fabric softeners
conditioners
Aliphatic amine/ phenylamine + acyl chloride
N-alkyl…amide + HCL
Explain why 3-aminopentane is a stronger base than ammonia
in 3-aminopentane the lone pair on N more available because of alkyl electron pushing / inductive effect
Explain the difference in base strength between amines E (C6H5NH2), F (C6H5CH2CH2NH2) and amine G (C6H5NHCH2CH3)
Strength depends on availability of the lone pair on the N
In E : N is next to the ring so the lone pair id delocalised into the ring and is less available.
in F/G : The N is next to alkyl groups so positive inductive effect/electrons pushed to N and lone pair more available.
E<G<F
