Amines & Amides Flashcards
What are amines?
Amines are produed when one or more hydrogen atoms in ammonia (NH3) are replaced by an alkyl group.
What is a primary/secondary/tertiary amine?
A primary amine is an amine with 1 alkyl group bonded to the nitrogen atom.
A secondary amine has 2 alkyl groups bonded to the nitrogen, and a tertiary amine has 3.
How are amines basic?
Amines can react with water to form an alkaline solution.
The lone pair of electrons on the amine’s nitrogen atom can accept a hydrogen ion from the H2O molecule (therefore acting as a base). This releases OH- ions in the solution (from the leftovers of H2O)
How can amines produce salts?
Amines react with acids to form an ammonium salt. Again, the amine acts as a base and accepts a proton (H+ ion) from the acid to form a quarternary ammonium salt.
e.g. butylamine + HCl -> butylammonium chloride
What is an aliphatic compound?
An aliphatic compound is a compound containing carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings.
When is an amine an aliphatic/aryl amine?
If the R group is an alkyl group (methyl, ethyl, etc) then then it is an aliphatic amine; if it is an aryl group (benzene ring or phenyl) then it is an aromatic amine.
Describe the solubility of amine salts
Like ammonium salts, amine salts are soluble ionic compounds, so when the alkyl group is small they are water soluble but become less so as the carbon chain increases.
How can primary amines be prepared?
- The reaction of halogenoalkanes with ammonia
- The reduction of nitriles
Describe the reaction of halogenoalkanes with ammonia
This is a nucleophilic substitution reaction in which the nitrogen lone pair in ammonia acts as a nucleophile and replaces the halogen in the halogenoalkane.
e.g. CH3CH2Cl + 2NH3 -> CH3CH2NH2 (primary amine) + NH4Cl
When a halogenoalkane is reacted with excess, hot ethanolic ammonia under pressure a primary amine is formed
Describe how the reduction of nitriles can form a primary amine
Nitriles contain a -CN functional group (triple bond) which can be reduced to an -NH2 group (by adding Hs)
The nitrile vapour and hydrogen gas (2H2) are passed over a nickel catalyst to form a primary amine.
Or LiAlH4 (a reducing agent) in dry ether can be used (provides 4 Hs).
Describe the reaction of halogenoalkanes with a primary amine
This is also a nucleophilic substitution reaction in which the nitrogen in the primary amine acts as a nucleophile and replaces the halogen in the halogenoalkane.
When a halogenoalkane is reacted with a primary amine in ethanoland heated in a sealed tube, under pressure a secondary amine is formed.
Tertiary amines can also be formed by further reaction of the secondary amine.
What is phenylamine?
Phenylamine is an organic compound consisting of a benzene ring and an amine (NH2) functional group.
Describe the two-stage reduction reaction of nitrobenzene to phenylamine
Stage 1 - Reduction of nitrobenzene
- Nitrobenzene, C6H5NO2, is reacted with tin, Sn, and concentrated hydrochloric acid, HCl
- Tin and hydrochloric acid act as reducing agents.
- The reaction mixture is heated under reflux in a boiling water bath
- The phenylammonium ions, C6H5NH3+, are protonated due to the acidic conditions. The NH3+ forms a salt with the Cl- ions from HCl.
Stage 2 - Formation of phenylamine
- The phenylammonium ions, C6H5NH3+, are deprotonated by the addition of excess sodium hydroxide solution, NaOH (aq).
Diagram of two-stage reaction of nitroenzene to phenylamine
Why is propylamine a stronger base than phenylamine?
The greater the electron density on an amine’s nitrogen atom, the more likely that lone pair is to be available for bonding.
Alkyl groups have a tendency to push electrons away from themselves and onto the nitrogen atom which is known as the positive inductive effect.
The more alkyl groups there are, the more available the lone pair of electrons is on the nitrogen atom.
In phenylamine, the lone pair on the nitrogen atom is delocalised into the ring which makes the lone pair less available to bond with an incoming proton (H+ ion)
What is the IUPAC name of this molecule?
N-methylpropylamine
(When naming a secondary amine, you must take care to name the alkyl groups alphabetically)
