What are amines?
Amines are derivatives of ammonia
What are the different structures of amines and describe them
- If one or more of the hydrogens in ammonia (NH3) is replaced with an organic group, you get an amine
- Primary amine: When one hydrogen is replaced with an organic group
- Secondary amine: When two hydrogens are replaced with two organic groups
- Tertiary amine: When three hydrogens are replaced with three organic groups
- Quaternary ammonium ion: The lone pair of electrons on the nitrogen atom in a tertiary amine can also bond with a fourth organic group.
Draw the structure of methylamine, dimethylamine, trimethylamine, tetramethylamine ion and phenylamine
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What is the purpose of quaternary ammonium salts
Used as cationic surfactants
How are quaternary ammonium salts used as cationic surfactants (6)
- Ammonium ions are positively charged
- Examples are tetramethylammonium chloride (CH3)4N+Cl-
- Quaternary ammonium salts with at least one long hydrocarbon chain are used as cationic surfactants
- The hydrocarbon tail will bind to non-polar substances such as grease whilst the cationic head will dissolve in water
- So they are useful for fabric cleaners and hair products
- In addition, the positively charged part (ammonium) will bind to negatively charged surfaces such as hair and fibre
How do amines act as a weak base?
- They have a lone pair of electrons on nitrogen that can form a dative covalent bond with an H+ ion
- So they accept protons
Strength of base depends on what? (3)
- Depends how available the lone pair of electrons on nitrogen is
- The more available the lone pair, is the more likely the amine will accept a proton, the stronger the base it is
- A lone pair of electrons will be more available is the electron density is higher
What are aliphatic amines?
- They are stronger bases than ammonia
- Ammonia is a stronger base than aromatic amines
Compare the availability of electrons and basic strength of a primary aromatic amine and a primary aliphatic amine
- Primary aromatic amine: The benzene ring draws electrons towards itself and the nitrogen lone pair gets partially delocalised onto the ring. So the electron density on the nitrogen decreases, making the lone pair much less available.
Primary aliphatic amine: Alkyl groups push electrons onto attached groups. So the electron density on the nitrogen atom increases. This makes the lone pair more available.
How are amines nucleophiles? and what is the effect of this (2)
- The lone pair of electrons the nitrogen atom makes amines nucleophiles
- They react with halogenoalkanes in a nucleophilic substitution reaction or with acyl chlorides and acid anhydrides in a nucleophilic addition-elimination reaction.
How are aliphatic amines made?
- Made from either halogenoalkanes or nitriles
Describe the process of making a nitrile from a halogenoalkane (6)
- Halogenoalkane is heated with ammonia
- Nucleophilic substitution reaction
- Recall back to first year
- If you make amines using this method, you end up with a mixture of primary, secondary and tertiary amines and quaternary ammonium salts.
- Because the primary amine produced first has a lone pair of electrons, its a nucleophile
- Nucleophile can react with remaining halogenoalkane in a nucleophilic substitution reaction.
Why cant a quaternary ammonium salt act as a nucleophile?
- It has no lone pair
How are aliphatic amines made with nitriles- method one
- By reducing the nitrile
- Reduce the nitrile into a primary amine by two methods
- You can use LiAlH4 (Lithium aluminum hydride) a strong reducing agent, in a non-aqueous solvent followed by a dilute acid
How are aliphatic amines made with the nitriles- method two
- By reducing the nitrile
- Reduce the nitrile into a primary amine by two methods
- LiAlH4, is fine for the lab but too expensive for industrial use
- Nitriles are reduced using hydrogen gas with a metal catalyst such as platinum or nickel at a high temperature and pressure. This called catalytic hydrogenation
Give the equation for the two methods of reducing nitriles to primary amines
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How are aromatic amines made? (4)
- Aromatic amines are made by reducing a nitro compound such as nitrobenzene
- Conditions: Heat a mixture of a nitro compound, tin metal and concentrated hydrochloric acid under reflux
- This makes a salt
- In turn the salt in turned to an aromatic amine when you add a an alkali such as sodium hydroxide to the solution
Draw the equation for the formation of an aromatic amine from nitrobenzene
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What are the real life purposes of aromatic amines?
- Dyes and pharmaceuticals
What are amides and what are their functional group?
- Carboxylic acid derivatives
- Functional group: -CONH2
- Carbonyl group pulls electrons away from the NH2 group, so amides behave differently from amines
Draw the structure of an amine in comparison to an amide
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