4.6 amines Flashcards
How do you tell if an amine is primary or secondary or even tertiary If the nitrogen is bonded to only one carbon atom
If the nitrogen is bonded to only one carbon atom, the compound is a primary amine, 1˚.
If the nitrogen is bonded to two carbon atoms, the compound is a secondary amine, 2˚.
If the nitrogen is bonded to three carbon atoms, the compound is a tertiary amine, 3˚.
If the nitrogen is bonded directly to a benzene ring, the compound is an aromatic amine.
Aromatic amines can be 1˚, 2˚ or 3˚.
How do you form an AMINE from a halogenoalkane
- React halogenoalkane with ammonia using a water/ethanol solvent eg CH3CH2Br+NH3 —> CH3CH3NH2+HBR
- Heat in a sealed tube and use excess ammonia
- Ammonia reacts with acidic HBR to give ammonium salt CH3CH2NH3+Br-
4.Amine reacts with ammonium salt so heating the salt with sodium hydroxide releases the amine.
Why does excess halogenoalkane create secondary amine
This happens because the amine acts as a nucleophile and attacks the Cδ+ atom of the C δ+ - Br δ- bond in a nucleophilic substitution reaction.
How do you form nitriles
Nitriles can be reduced with a suitable reducing agent such as lithium tetrahydridoaluminate(III) LiAlH4
How do you make phenyl amine
Reduction of nitrobenzene Reducing agent is tin (Sn) and concentrated HCl Reflux in boiling water to get phenylammonium ions. Add NaOH to salt to phenylamine
How do you separate phenylamine
- steam distilling to produce a distillate containing phenylamine and water
- using a separating funnel to obtain the immiscible phenylamine
-drying to remove traces of water
-redistilling to produce pure phenylamine.
Why are amines basic Amines
Amines, like ammonia, have a lone pair of electrons on the nitrogen atom. This allows amines to accept a proton by means of a coordinate bond
The shorter chain amines will react with water, establishing an equilibrium:
CH3NH2 + H20 ⇌ [CH3NH3]+ + OH-
The equilibrium lies well over to the left, therefore amines are weak bases.
Why are alkylamines stronger bases
Alkylamines, e.g. ethylamine, are stronger bases than ammonia because the alkyl groups ‘push’ electrons more onto the nitrogen atom, making it more δ- when compared with ammonia’s nitrogen.
Why is phenylamine a weaker base than ethylamine
Phenylamine is a much weaker base than ethylamine as the lone pair of electrons on the nitrogen becomes part of the delocalised π-electron system of the benzene ring. This makes the nitrogen relatively less δ-.
List the following in increasing basticity and explain why
These are all basic because the lone pair of electrons on the nitrogen can accept a
proton.
1. Propylamine is a stronger base than ammonia because the alkyl groups ‘push’ electrons more onto the nitrogen atom therefore increasing the availability of the lone pair.
2. Phenylamine is a weaker base than ammonia as the lone pair of electrons on the nitrogen atom becomes part of the delocalised π-electron system of the benzene ring.
This makes the lone pair less available to bond with a H+ ion.
What is the boiling point trend of amines?
The boiling temperatures of amines (and alkanes) increase as the chain length increases. This is because there are more van der Waals forces between the molecules
Why do amines have stronger boiling points than alkanes
This is because amines can form hydrogen bonds as well as van der Waals forces between molecules. Hydrogen bonds form between the lone pair of electrons on the electronegative nitrogen atom in one molecule and the slightly positive hydrogen atom in another molecule.
Why are boiling points lower in secondary amines
The boiling temperature of the secondary amine,(CH3)2NH, is lower than the corresponding primary amine, CH3CH2NH2. This is because there is less surface contact between the molecules resulting in weaker van der Waals forces between the molecules
Why do amines have lower boiling points than alcohols?
Alcohols (and carboxylic acids) also form hydrogen bonds between molecules. However, amines have lower boiling points than alcohols because nitrogen is less electronegative than oxygen, so the hydrogen bonds between the amine molecules are weaker than those between alcohol molecules
Describe the solubility of amines
All of the amines can form hydrogen bonds with water. Therefore the small amines are very soluble in water.
Solubility decreases as the hydrocarbon chain increases - especially after about six carbons. The hydrocarbon chains break more hydrogen bonds between water molecules than are made between water and the -NH2 groups. Phenylamine is only slightly soluble in water due to the hydrophobic nature of the benzene ring.
Why does propylamine have higher BP than trimethylamine
Propylamine has a higher boiling temperature than trimethylamine because there is greater surface contact between the molecules resulting in stronger van der Waals forces between the molecules
How do you form an amide from amine
Amines act as a nucleophillic and they attack the Cδ+ atom of the carbonyl group in ethanoyl chloride to form an amide.
Describe the reaction of amine with nitric acid Nitric(III) acid (or nitrous acid)
Nitric(III) acid (or nitrous acid), HNO2, is unstable and is always prepared in situ. It is usually made by reacting sodium nitrate(III), (or sodium nitrite), NaNO2 with hydrochloric acid
Describe the reaction of aliphatic amines with nitric acid
Aliphatic amines react with nitric(III) acid with the evolution of nitrogen, so bubbles of colourless gas are seen.
Describe the reaction of aromatic amine with nitric acid
For a primary aromatic amine, e.g. phenylamine, if the temperature is between 0 ˚C and 10˚C, a solution containing the stable benzene diazonium ion is formed.
What can be used as a test to distinguish between aromatic and aliphatic amines using cold nitric(III) acid can be used as a test to distinguish between aliphatic and aromatic amines
using cold nitric(III) acid can be used as a test to distinguish between aliphatic and aromatic amines
What is coupling
The diazonium ion -N=N- is a weak electrophile and requires a highly electron-rich aromatic ring to undergo electrophilic substitution. Functional groups like -OH or -NH2 on the benzene ring increase its electron density (a process called activation),
making it more reactive towards diazonium ions and facilitating azo coupling.
What is a chromophore
A chromophore is the part of the molecule that is responsible for its colour
A chromophore is a region in the molecule where the energy difference between two separate molecular orbitals falls within the range of the visible spectrum i.e. wavelengths from about 380 to 740 nm. In Azores it is -N=N-
How do you see light in azodyes
If radiation is absorbed in the visible region the colour seen is the colour that is not absorbed. As a rule of thumb the colour absorbed by a compound is the opposite of the colour that is seen.
A certain azo dye appears red in white light. State and explain the colour observed
In red light appears red
In blue green light appears black
How are frequency and wavelength related c = fλ (c is the speed of light)
c = fλ (c is the speed of light)
The frequency of electromagnetic radiation and energy are connected by the equation:
E = hf (h is Planck’s constant)
Since f ∝ 1/λ - if frequency increases, wavelength decreases.
Also, f ∝ E - so if frequency increases, energy increases.
Explain why both propylamine and phenylamine can act as bases
Both molecules have a lone pair of electrons on the nitrogen These lone pairs can form co ordinate bonds with H+ ions
