Amines & Amides Flashcards
What are amines?
-nitrogen containing organic compounds derived from ammonia where one or more of the hydrogen have been replaced by an alkyl group.
Why do primary amine have higher boiling points compared to alkanes of the same length?
-because they can hydrogen bond with each other plus London and dipole-dipole.
Why are the boiling points of secondary amines lower in comparison to primary amines with the same number of carbon atoms ?
-even though secondary amines can still form hydrogen bonds they have the nitrogen atom in the middle of the chain rather than at the end makes the permanent dipole on the molecule slightly less.
(The lower b.p due to lower dipole-dipole)
Compare the bp of tertiary amines against primary and secondary?
-in the tertiary amines there aren’t any hydrogen atoms attached directly to the nitrogen , this makes hydrogen bonding between tertiary molecules impossible thus a lower boiling point.
Are amines soluble in water?
-smaller chain amines are soluble in water since they can form hydrogen bonds with water even tertiary amines.
Why does solubility fall as the hydrocarbon chain of an amine gets longer?
- this is because the hydrocarbon chains have to force their way between water molecules, breaking hydrogen bonds between water molecules.
- this makes the reaction less energetically feasible
Preparing amines from halogenoalaknes? Conditions
- heat the halogenoalkane with ammonia in ethanolic solution
- sealed test tube under pressure
- nucleophilic substitution.
How would you make a primary amine from nucleophilic substitution of halogenoalkane?
-use excess ammonia so that the amine doesn’t further react
Why does the reaction with ammonia and halogenoalkane carry on if excess ammonia isn’t used?
-since the amine formed has a lone pair of electrons on the nitrogen it will compete with ammonia attacking the halogenoalkane forming a secondary amine.
Preparing amines from nitriles?
- nitriles can be reduced to primary amines using H2 at high temperature and pressure in the presence of a nickel catalyst. (Used in the industry)
- they can also be reduced to primary amines using strong reducing agents - LIAlH4 in dry ether and an acid catalyst (this is too expensive for the industry)
Preparation of aromatic amines?
- tin is used as a reducing agent mixed with conc HCl acid
- it’s heated under reflux
When do amines act as a base?
-when they bond with a H+ ion
Definition of basicity of a base?
- is the extent it which it can donate a lone pair of electrons to the hydrogen atoms of a water molecule.
What’s the product from the reaction of an amine with water?
-ammonium ion, which forms a salt with an anion
How could you regenerate the soluble amine from the ammonium salt?
-adding a strong base -> removes the H+ ions
In order to be the strongest base what must a particular amine have (out of a set of amines)?
- greatest electron density around the N atom making it better electron pair donor
Out of ammonia, primary aliphatic and primary aromatic amines what is the strongest base? Explain?
- primary aliphatic amines are the strongest whilst aromatic amine are the weakest
- the aromatic amines are the weakest base because the lone pair on nitrogen is partially delocalised into the ring and therefore decreases the attraction of H+ ion.
- primary aliphatic amines are stronger bases than ammonia as the alkyl groups are electron releasing and push electrons towards the nitrogen atoms making it a stronger base.
What effect do alkyl groups have on the electron density and base strength?
- positive inductive effect - increase electron density around N —> stronger base
Explain the reaction and what you’ll see between a small amount methylamine solution + copper (II) ions?
-a pale blue ppt , not soluble
What will you see when you react a more methylamine with copper ions?
- a deep blue solution that is soluble.
