amines

What are amines?

Compounds based on ammonia where the H atoms have been replaced by alkyl or aryl groups

What is a primary aliphatic amine?

A straight chain (I.e. not aromatic) amine with one alkyl/aryl group bonded to the nitrogen

What are the two methods of producing primary aliphatic amines?

Nucleophilic substitution of halogenoalkanes with ammonia

Reduction of nitriles

Give a use of aromatic amines

MAKING dyes

i.e. in the manufacture of dyes

What is a primary amine?

An amine containing 1 alkyl/aryl group bonded to the N
1 H has been replaced (in NH3)

What is a secondary amine?

An amine containing 2 alkyl/aryl groups bonded to the N
2 H's have been replaced (in NH3)

What is a tertiary amine?

An amine containing 3 alkyl/aryl group bonded to the N
3 H's have been replaced (in NH3)

How are Quaternary ammonium salts produced? (2 ways)

From tertiary amines:
N lone pair of electrons forms dative covalent bond to a 4th alkyl group
From ammonia:
N lone pair of electrons forms dative covalent bond to 4th H

What is a quaternary ammonium salt?

A crystalline solid
4 alkyl groups bonded to the N atom
4 H bonded to the N atom

What are quaternary ammonium salts ionic compounds?

There is an electrostatic attraction between the positive quaternary ammonium ion and negative anion, this is the ionic bond.

What is the order of priority for organic chemistry ? (Highest to Lowest)

Carboxyl -COOH
Aldehyde -CHO
Ketone- CO-
Hydroxyl - OH
Amine -NH2 -RNH - R2N
Alkene -C=C-

Give the conditions needed to produce a primary amine from a halogenoalkane

Excess ammonia in ethanol, pressure, sealed glass tube.

Why does ammonia act as a nucleophile?

Has lone pair of electrons

Why are halogenoalkanes vulnerable to nucleophilic attack?

The polar C-X group.
Delta positive carbon is an electron deficient centre

What is the name of the mechanism by which amines are produced from halogenoalkanes?

Nucleophilic substitution

Why can further substitution occur in nucleophilic substitution of halogenoalkanes?

The amine produced is a nucleophile, has a lone pair of electrons on N and can attack another molecule of the halogenoalkane

Under what condition is the primary amine the major product?

Excess ammonia

Under what condition will further substitution occur?

Excess halogenoalkane

Why is nucleophilic substitution not usually used to prepare amines?

Other products (unwanted) produced because of further substitution

What is the name of the reaction by which amines are produced from nitriles?

Reduction

What is the reducing agent for the reduction of nitriles?

LiAlH4 in dry ether

What is the condition for the reducing agent ? (nitriles to amines)

In dry ether

What is the other way of reducing nitriles to amines? (not LiAlH4)

H2 and nickel catalyst

Give the equation for the reduction of a nitrile using H2 and nickel catalyst

R-C≡N + 2H2 --> R-CH2NH2

Give the equation for the reduction of a nitrile using LiAlH4

R-C≡N + 4[H] --> R-CH2NH2

Why does preparation of amines from nitriles give a higher yield than from halogenoalkanes?

No other products

How can amines be prepared from benzene ? (2 steps)

-Nitration of benzene
-Reduction of nitrobenzene

What reagents are needed in the reduction of nitrobenzene?

Sn / conc HCl

What is the reducing agent in the reduction of nitrobenzene ?

Conc HCl

What are the 4 conditions for reducing nitrobenzene?

-Heat under reflux
-Tin, Sn
-Conc HCl
-Add Conc NaOH

Why is conc NaOH added when reducing nitrobenzene?

To remove the H+ from the NH3+ group and release the free amines

What is the phenylammonium ion?

C6H6-NH3+

How is the phenylammonium ion formed?

-Excess acid is used in reduction of nitrobenzene
-Phenylamine acts as a base and accepts H+

Why are amines bases?

the lone pair of electrons on N and because they accept H+ in the dative covalent bond

Put the following in order of base strength (strong to weak)
Primary Aliphatic Amines/ Ammonia/ Primary Aromatic Amines

Primary Aliphatic Amines
Ammonia
Primary Aromatic Amines

Why are primary aliphatic amines stronger bases than ammonia?

Alkyl group bonded to N
Positive inductive effect (electron donating)
Increases electron density on N
Availability of the lone pair increases
More readily available to accept a proton

Give the general equation for the reaction between ammonia and acid

Ammonia + acid --> ammonium salt

Give the general equation for the reaction between an amine and an acid

Amine + acid --> alkyl ammonium salt

How can amines/ammonia be liberated (released) from their salt?

Using dilute alkali

Give the general equation for the reaction between an amine and water

Amine + water --> alkylammonium ion + OH-

Why is the solution formed when amines react with water weakly alkaline?

Amine partially ionised
Equilibrium lies to the left
Low [OH-]

Why are primary aromatic amine weaker bases than ammonia and primary aliphatic amines?

Lone pair of electrons on N
Delocalised into pi system of delocalised electrons
Lower electron density on N
Lone pair less available to accept a proton

If excess halogenoalkane is used in nucleophilic substitution , what will the final product be?

Quaternary ammonium salt

Why does no further substitution occur with the quaternary ammonium salt?

-No longer lone pair of electrons on N
- cannot act as a nuc;leophile

Give the use of quaternary ammonium salts and 3 examples of this

-Catatonic surfactant
- detergents
- fabric softeners

Write the equation for the reaction between an acyl chloride and ammonia

Acyl chloride + ammonia --> amide + HCl
HCl + NH3 --> NH4Cl

Write the equation for the reaction between an acyl chloride and primary amine

Acyl chloride + primary amine --> N-substituted amide + HCl
HCl + amine --> Alkyl ammonium salt

Write an equation for the reaction between and acid anhydride and ammonia

Acid anhydride + ammonia --> Amide + carboxylic acid
Carboxylic acid + ammonia --> ammonium alkanoate

Carboxylic acid + ammonia --> ammonium alkanoate

Write the equation for the reaction between an acid anhydride and primary amine

Acid anhydride + primary amine --> N-Substituted amide + carboxylic acid
Carboxylic acid + primary amine --> alkylammonium alkanoate
e.g. methylammonium ethanoate

What is observed when ammonia reacts with acyl chlorides?

Vigorous reaction
White smoke produced
Some mixture remains dissolved in water as colourless solution