Organic - 3.11 Amines Flashcards
What is the structure of amines based on?
Ammonia, where hydrogen atoms have been replaced by alkyl or aryl groups.
What are the hydrogen atoms replaced with in amines?
Alkyl or aryl groups
What are quaternary ammonium compounds produced from?
Produced from tertiary amines where the nitrogen’s lone pair of electrons forms a dative covalent bond to the 4th alkyl group.
How many alkyl groups does a quaternary ammonium salt have?
Four
What is the shape of NH4+ and why?
Tetrahedral, four bonding pairs spread equally
What is the shape of NH3 and why?
Pyramidal, lone pair exerts a stronger repulsive force
What is the bond angle in amines?
107
What prefix is used if there are two identical R groups attached to a nitrogen?
di-
What prefix is used if there are three identical R groups attached to a nitrogen?
tri-
How are the groups ordered if there are two different alkyl or aryl groups present?
They are ordered alphabetically
When is the amine group denoted using amino-?
If other functional groups are present in the molecule
What is the hierarchy used in organic chemistry?
- Carboxyl (-COOH)
- Aldehyde (-CHO)
- Ketone (-CO-)
- Hydroxyl (-OH)
- Amines (-NH2, -RNH, -R2N)
- Alkene (-C=C-)
What do halogenoalkanes and ammonia form?
Amines
What are the conditions for the preparation of primary amines from halogenoalkanes?
Heat in a sealed flask with excess ammonia in ethanol.
What is the type of reaction for the preparation of primary amines from halogenoalkanes?
Nucleophilic Substitution
What is the overall reaction for the preparation of primary amines from halogenoalkanes?
R-X + 2NH3 -> R-NH2 + NH4X
What are the conditions for the preparation of primary amines from nitriles by reduction?
Using hydrogen in the presence of a nickel catalyst or by using a reducing agent such as LiAl4 in ether.
What are the two steps involved in the preparation of primary amines from nitriles?
1) Formation of a nitrile from a halogenoalkane
2) Reduction of the nitrile to form an amine
How are aromatic amines prepared?
Prepared by the reduction of nitro compounds
How is phenylamine prepared?
By reduction of nitrobenzene using tin and conc sulfuric acid as a reducing agent
What are the conditions for the preparation of phenylamine?
Heat under reflux with tin and excess sulfuric acid, followed by adding conc NaOH.
Why is concentrated NaOH added in the preparation of phenylamine?
To remove the hydrogen ion from the NH3+ group. The addition of concentrated alkali liberates the free amine.
What are aromatic amines used for?
Used in the manufacture of dyes (azo dyes)
What are the two basic properties of amines?
Weak bases
Lone pair of electrons on nitrogen atom of ammonia and amines accept a proton.
What are two formulas for the reaction of amines with dilute mineral acids?
ammonia + acid -> ammonium salt
amine + acid -> alkyl ammonium salt
What is the equation for the reaction of an amine with dilute HCl?
CH3NH2 + HCl -><- CH3NH3+Cl-
Methylamine + hydrochloric acid -><- phenylammonium chloride
(Reversible reaction)
What is the equation for the reaction of an amine with dilute H2SO4?
2CH3CH2NH2 + H2SO4 -><- (CH3CH2NH3)2SO4
ethylamine + sulfuric acid -><- ethyl ammonium sulfate
(Reversible reaction)
What happens when an amine reacts with water?
They accept a hydrogen ion from water to produce an alkylammonium ion and hydroxide ion.
How does base strength decrease in amines?
Strongest: Primary Aliphatic Amine
Ammonia
Weakest: Primary Aromatic Amine
Why are primary aliphatic amines stronger bases than ammonia?
Because of the alkyl group attached to the nitrogen. Alkyl group is electron donating causing a lone pair to be more available
Why are primary aromatic amines weaker bases than ammonia?
Weaker bases because nitrogen’s lone pair of electrons can overlap with the delocalised pi electrons in the benzene ring. Lone pair is less available for accepting a proton.
What makes amines nucleophiles?
They all contain a lone pair of electrons so they act as nucleophiles.
What are the two steps in making a primary amine?
An amine and halogenoalkane react and initially a salt is formed.
Then the salt reacts with excess ammonia to form a primary amine.
How is a secondary amine formed from a primary amine?
Further substitution reactions may occur. This is because the primary amine produced has a lone pair so it can act as a nucleophile and continue to react with any unused halogenoalkane.
How is a tertiary amine formed from a secondary amine
The secondary amine produced also has a lone pair so it can act as a nucleophile.
How is a quarternary ammonium salt formed from a tertiary amine?
The tertiary amine reacts with the halogenoalkare to form a quarternary ammonium salt.
What are the conditions required for a primary amine to be produced?
Excess ammonia
What are the conditions needed to produce a quaternary ammonium salt?
Excess halogenoalkane
What are quarternary ammonium salts used for?
Cationic surfactants: found in detergents, fabric softeners and hair conditioners.
