28 - Amines Flashcards
(32 cards)
What are aromatic amines?
When the NH2 group is directly attached to the benzene group.
What are aliphatic amines?
Non-aromatic amines.
What are secondary and tertiary amines?
2 - two R groups attached to the N
3 - three R groups attached to the N
What are quaternary ammonium salts?
When 4 R groups are attached to the N
What are amines?
RNH2
What is the naming of amines?
suffix -amine
letter N- used to indicate alkyl groups attached to the nitrogen.
If it is not the dominant functional group prefix -amino used
What is the shape and bond angles of ammonia?
Pyramidal
107
What is the boiling point of amines compared to alkanes and alcohols?
Amines are polar so they can hydrogen bond to one another using their -NH2 groups, so they have a higher boiling point than alkanes. (Also have stronger vdw due to a greater Mr)
Nitrogen is less electronegative than oxygen so they have a lower boiling point than comparable alcohols.
What is the solubility of amines like?
Very soluble in water and alcohols, due to hydrogen bonding with the solvent. The solubility decreases as chain length increases.
Soluble in organic solvents.
What two things can amines act as?
Bronstead-Lowry bases, as they can accept a proton, due to the lone pair of electrons.
Lewis bases, as they can act as a nucleophile and be lone pair donators.
What do amines and acids form?
Ammonium salts.
What does the strength of an amine base depend on?
How readily it will accept a proton, so the greater the electron density on the N the greater its basicity.
How do electron releasing groups affect the basicity of amines?
The electron density on the N increases, making the lone pair more effective, increasing basicity.
(Alkyl groups)
Why are aryl amines worse bases than alkyl amines?
Aryl groups are electron withdrawing from the nitrogen, as the lone pair of electrons overlap with the delocalised system on the benzene ring, the aromatic ring and nitrogen’s lone pair of electrons are delocalised, making the lone pair less available, therefore decreasing basicity.
Which amines are the best bases?
Secondary alkylamines
Tertiary alkylamines (as less soluble in water)
Primary alkylamines
Ammonia
What are the reagents for amines produced from halogenoalkanes and ammonia?
Halogenoalkane + excess ethanoic ammonia
What are the conditions for amines produced from halogenoalkanes and ammonia?
Reflux
Ethanoic
Under pressure.
What is the mechanism for amines produced from halogenoalkanes and ammonia?
Nucleophilic substitution.
Why is ammonia used in excess for the reaction of halogenoalkanes and ammonia?
To prevent further substitution, as the primary amine can act as a nucleophile to from secondary, tertiary and quarternary ammonia salts.
How are primary alkyl amines prepared from halogenoalkanes?
Halogenoalkane + cyanide ions in aqueous ethanol to form a nitrile by nucleophilic substitution.
Nitrile reduced to primary amines with hydrogen/ nickel catalyst, by hydrogenation.
What are the reagents for the formation of phenylbenzene from benzene?
conc. sulfuric acid + conc. nitric acid to form a NO2+ electrophile.
Then tin and HCl
What are the steps for the formation of phenylamine from benzene?
Electrophilic addition with NO2+ to form nitrobenzene.
Nitrobenzene reduced using tin and HCl , which react to form hydrogen, which reduces it by removing oxygen atoms.
As HCl is used a salt is formed, so NaOH is used to liberate the free amine.
What are amides and their naming?
CONH2
suffix - amide
Compare the boiling points of 1,2,3 amides?
Primary amides have a greater boiling point than secondary amides as there are more hydrogens attached to the nitrogen, so more hydrogen bonds are formed. Tertiary amides have the lowest melting point as they can’t form hydrogen bonds.
