Amines Flashcards
What is the functional group of amines?
A nitrogen atom directly bonded to a carbon atom of an alkyl or aryl group.
Suffix: -amine
What is a primary amine?
The nitrogen is directly bonded to one carbon.
What is a secondary amine?
The nitrogen atom is directly bonded to two carbon atoms.
What is a tertiary amine?
The nitrogen atom is directly bonded to three carbon atoms.
How can you make an amine from a halogenoalkane?
Add ammonia and a water/ethanol solvent.
What occurs when the halogenoalkane is warmed when producing an amine?
Ammonia gas is lost, reducing the yield, so we put the reactants in a sealed tube which is gently heated.
Why is an excess of ammonia used in the halogenoalkane reaction to an amine?
To ensure the reaction is complete and to react with the acidic HBr to give ammonium bromide.
What occurs when an excess of halogenoalkane is used in the reaction to an amine?
Further substitution occurs to give a secondary amine. This occurs because the amine acts as a base and attacks the C of the C-Br bond.
What is the mechanism in the conversion of a halogenoalkane to an amine?
Nucleophillic substitution.
What occurs when an ammonium salt is heated with a base?
Ammonia is produced.
How are nitriles reduced to amines?
Using LiAlH4 dissolved in ethoxyethane as a solvent.
How is phenylamine made?
From the reduction of nitrobenzene as benzene is not easily attracted by nucleophiles such as ammonia, as the ring electrons repel nucleophiles, but are attracted to electrophiles.
What are the reducing agents for the reduction of nitrobenzene to phenylamine?
Tin metal and HCl.
Describe the method for converting nitrobenzene to phenylamine
Add Tin metal and HCl and heat to 100°C for 30 minutes. The product at this stage is a complex Tin (IV) oxide. After cooling the mixture, aqueous NaOH is added to decompose the salt to phenylamine, NaCl and Tin (IV) oxide. The mixture is then steam distilled to produce a distillate containing phenylamine and water. The immiscible phenylamine is separated, dried to remove any traces of water and redistilled.
How does the lab preparation differ from the commercial production of phenylamine?
Making phenylamine commercially requires more economical reducing agents such as hydrogen and a nickel catalyst or iron and hydrochloric acid.
How do amines react?
They have a lone pair of electrons on the nitrogen atom which can be used to accept a proton by means of a co-ordinate bond.
Order the basicitiy of methylamine, phenylamine and ammonia
Phenylamine < Ammonia < Methylamine
Describe the basicity of methylamine
It is a stronger base than ammonia because the alkyl groups push electrons slightly towards the nitrogen, making it more δ-.
Describe the basicity of phenylamine
Phenylamine is a much weaker base than ammonia as the nitrogen’s lone pair becomes part of the delocalised π system, making the nitrogen less δ-.
Describe the solubility of phenylamine
Although the -NH2 group can hydrogen bond with water, phenylamine is only slightly soluble because of the hydrophobic effect of the benzene ring.
How do amines react with acid chlorides?
The nitrogen lone pair allows amines to act as nucleophiles, attacking the δ+ carbon atom of the carbonyl group in an acid chloride.
What is the organic product of the reaction between methylamine and an acid chloride?
N-methylethanimide. The N means the methyl group is bonded to the nitrogen atom.
How is nitric (III) acid formed?
By the reaction of dilute HCl on sodium nitrate (III).
How does a primary aliphatic amine react with HNO2?
It forms a primary alcohol and N2 gas.
What is the disadvantages to the formation of alcohols from amines?
The yield of alcohol is poor.
What happens if aqueous H2SO4 is used instead of HCl in the amine to benzenedizonium ion reaction?
The intermediate becomes benzenedizonium hydrogensulfate. And above 10°C, decomposition of the benzenedizonium compound occurs, giving phenol.
What are the reagents and conditions to turn a primary aromatic amine to produce a benzenedizonium ion?
NaNO2 and HCl, at 0 to 10°C.
How do benzenedizonium compounds react below 10°C?
They react with phenols are aromatic amines to produce compounds where the -N=N- azo group is retained.
How do benzenedizonium ions react?
They are weak electrophiles and will bond via electrophillic substitution with aromatic compounds where the ring has been activated by the presence of an -OH or -NH2 group.
What is the product of the reaction between a benzenedizonium ion and an amine or phenol?
A highly coloured azo dye.
What is the azo dye making reaction called?
A coupling reaction and is carried out in alkaline solution. Coupling often occurs at the -4 position but can occur at the -2 position relative to the -OH or -NH2 group.
What is a chromophore?
A structural unit in a molecule that is primarily responsible for the absorption of radiation at a certain wavelength, generally in the visible or ultraviolet region.
What occurs if light is absorbed in the visible range?
The colour that is not absorbed is the colour observed.
What does the actual wavelength of light absorbed depend on?
The other groups present in the molecule.
What does the intensity of the colour observed depend on?
The concentration of the compound present.
