Chapter 27 Flashcards
What are amines?
- Compounds derived from ammonia, where one or more of the H atoms are replaced by a carbon chain
In what 2 ways can amines be classified?
- Primary, secondary and tertiary
- Aliphatic or aromatic
What are aliphatic and aromatic amines?
- In aliphatic amines the N atom is attached to at least one straight or branched carbon chain
- In aromatic amines the N atom is attached to an aromatic ring
What are primary, secondary and tertiary amines?
- A primary amine is bonded to 1 alkyl or aryl groups
- A secondary amine is bonded to 2
- A tertiary amine is bonded to 3
How are primary amines named? Give examples.
- If the amine is at the end of the chain, you add the suffix -amine (e.g. ethylamine)
- If the amine is not on carbon 1, you use the prefix amino- (e.g. 2-aminobutane)
How are secondary and tertiary amines named?
- If they’re attached to multiples of the same alkyl chain, you use the prefix di- or tri- (e.g. dimethylamine)
- If they’re attached to different alkyl chains, use the short one as a prefix (if there are 2 other chains, put them in alphabetical order) and add an N to show that the other chain is also bonded to the nitrogen atom (e.g. N-methylpropylamine, N-ethyl-N-methylpropylamine, N,N-dimethylethylamine)
What can amines can act as in chemical reactions?
- Weak bases, as the lone pair on the N atom can accept a proton and form a dative covalent bond
- Nucleophiles, as there is a lone pair of electrons on the N atom
How do amines react with acids? Give an example.
- They form an ammonium salt
- Hydrochloric acid + propylamine -> propylammonium chloride
How can primary amines be prepared?
- Salt formation: reacting a haloalkane with ammonia to form an ammonium salt
- Amine formation: reacting the ammonium salt with sodium hydroxide to form the primary amine
How are secondary and tertiary amines formed?
- To form secondary amines, the process to form primary amines repeats, but with a primary amine taking the role of ammonia (the N still has a lone pair)
- To form tertiary amines, secondary amines are reacted with a haloalkane
Give the equations for the formation of propylamine. Give the conditions, and mechanism if applicable.
- Step 1: nucleophilic substitution
- Excess ethanolic ammonia
- 1-chloropropane + ammonia -> propylammonium chloride
- Step 2: check mechanism
- propylammonium chloride + sodium hydroxide -> amine + sodium chloride + water
Why is excess ethanolic ammonia used in the formation of primary amines?
- Ethanol is used as a solvent instead of water, as otherwise the haloalkane would react with water via nucleophilic substitution to form an alcohol
- Excess ammonia is used to reduce (although it’s not possible to entirely avoid) further substitution of the amine to form secondary and tertiary amines
How are aromatic amines prepared?
- Nitrobenzene is reduced using tin and concentrated hydrochloric acid
Give the reaction and conditions for the formation of phenylamine.
- Nitrobenzene + 6[H] -> phenylamine + 2H2O
- Conditions: Sn and concentrated HCl
What are amino acids?
- Compounds with an amine group on one end, and a carboxyl group on the other
What are α-amino acids, and how do they differ?
- They only have one central carbon atom which has a H group, and an R group
- The R group is what differs between them
How do amino acids react with acids?
- The amine group reacts to form an ammonium salt (NH3+X)
How do amino acids react with aqueous alkalis?
- The carboxyl group reacts to form a carboxylate salt and water
How do amino acids react with alcohols?
- If an amino acid is heated under reflux with an acid catalyst, it forms an ester and water
- The amine group is also protonated due to the acidic conditions
What is optical isomerism?
- A type of stereoisomerism
What are optical isomers? What is a pair of optical isomers called?
- Stereoisomers that are non-superimposable mirror images of each other (think hands)
- (Superimposable: can perfectly overlap if they were in the same place)
- The pair are called enantiomers
What causes optical isomerism?
- One or more chiral centres in a molecule
What are chiral centres?
- Chiral centres are usually carbon atoms that are bonded to 4 other groups; this makes them asymmetric (if it was bonded to less than 4 groups, or 2 or more of the same group, you can split the molecule in half and it would look the same)
How is the number of chiral centres linked to the number of enantiomers?
- Number of enantiomers: 2^n
- n: number of chiral centres
What is condensation polymerisation?
- The joining of monomers with the loss of a small molecule
Give 2 examples of types of polymers formed through condensation polymerisation.
- Polyesters
- Polyamides
What is required for condensation polymerisation to take place?
- 2 different functional groups
What are the 2 ways of making polyesters? What small molecule is made in each reaction, and how much is formed?
- Making them from one monomer that has both a hydroxyl and a carboxyl group
- n-1 water molecules are formed
- Making them from 2 different monomers where one is a dicarboxylic acid and the other is a diol
- 2n-1 water molecules are formed
How else can polyesters be formed? What difference is there in the reaction?
- Using acyl and diacyl chlorides instead of carboxylic and dicarboxylic acids
- HCl is formed instead of water
What are the 4 ways of making polyamides? What small molecule is made in each reaction, and how much is formed?
- Making them from one monomer that has both an amine and a carboxyl group
- n-1 water molecules are formed
- Making them from one monomer that has both an amine and an acyl chloride group
- n-1 HCl molecules are formed
- Making them from 2 different monomers where one is a dicarboxylic acid and the other is a diamine
- 2n-1 water molecules are formed
- Making them from 2 different monomers where one is a diacyl chloride and the other is a diamine
- 2n-1 HCl molecules are formed
What are the 2 main differences between addition and condensation polymerisation?
- Addition polymerisation uses a monomer with a C=C, while condensation polymerisation uses either one monomer with 2 functional groups, or 2 monomers where each has 2 of the same functional group
- In addition polymers, there is a constant carbon chain, while in condensation polymers there are ester and amide linkages
In what way do polyesters behave in the same way as esters?
- They can both be hydrolysed by aqueous acid or alkali
What does the hydrolysis of polyesters by acid produce?
- Carboxylic acid and alcohol
What does the hydrolysis of polyesters by aqueous alkali produce?
- Carboxylate salt and alcohol
What does the hydrolysis of polyamides by acid produce?
- Alkylammonium ion and carboxylic acid
What does the hydrolysis of polyamides by aqueous alkali produce?
- Carboxylate salt and amine
Why are some polyesters biodegradable?
- They can be hydrolysed
