Chapter 28 - Amines Flashcards
What is an amine?
It can be thought of as any organic molecule derived from ammonia, where any of the hydrogen atoms have been replaced by alkyl or aryl (aromatic) groups. They are very reactive and usually used as intermediate compounds
What is the difference between primary, secondary and tertiary amines?
This refers to how many substiuent groups the nitrogen atom is bonded to, or how many R groups
What is an aliphatic amine?
An amine which does not contain any aromatic rings
How can you form primary aliphatic amines?
They can be formed by nucleophilic substiution of ammonia with a halogenoalkane
They can be formed by reducing nitrile groups
How can you form aromatic amines? Uses?
Reduction of the nitro group in arene rings, used as industral dyes
What can amines act as and why?
They can act as weak bases due to the presence of the lone pair on the nitrogen atom
How does the basic strength of ammonia, primary secondary and tertiary amines, and aromatic amines compare?
The weakest bases are the aromatic amines, because the arene ring withdraws electrons from the nitrogen into the delocalised ring, making it less negative so the nitrogen struggles to attract H+ ions more. Ammonia is next because it has no positive inductive effect, making amines stronger bases than ammonia. This is because the nitrogen atom pulls electrons in from its carbon bonds making it more negative and therefore stronger at attracting H+ ions. Secondary have 2 alkyls and are therefore stronger than primary, however tertiary are less soluble in water due to the lack of hydrogen bonds therefore they are not stronger bases than secondary amines
Why can it be difficult to produce primary amines? How best to produce them?
It is difficult because of the fact that all amines continue to be nucleophiles, and therefore will keep reacting with halogenoalkanes to produce secondary and tertiary amines and then quarternary ammonium salts. The best way to maximised yield of primary amines is by using a large excess of ammonia
What is the advantage to substituting a halogenalkane with a cyanide then reducing it as opposed to substituting the halogenoalkane with ammonia?
The cyanide group will increase the chain length of the halogenoalkane by one, and the product will be more pure because only primary amines can be formed this way
What conditions are required to form and then reduce the nitrile?
The halogenoalkane and cyanide need to react in aqueous ethanol, and then the reduction requires a nickel or hydrogen catalyst
What conditions are required to form a phenylamine?
Concentrated nitric acid and sulfuric acid need to react to form the nitrobenzene, which is then reduced by hydrochloric acid and a tin catalyst. However, because of the HCl it forms a salt based product, so NaOH needs to be added to liberate the free amine
What can quarternary ammonium salts be used as?
Cationic surfactants - cationic because they have a positive charge and surfactants because they allow the mixing of immiscible liquids, allowing wetting to take place, very useful as hair and fabric conditioners
What is an amide?
A compound with the formula O = C - N (-H)
How are amides formed?
When an acid chloride or anhydride reacts with a primary amine in an addition-elimination reaction
Outline the mechanism between ethanoyl chloride and methyamine
Addition-elimination
The double bond on the nitrogen bonds to the partially positive carbon as the double bond on the oxygen breaks one of its bonds which goes to the oxygen (making it negatively charged), making the amine positively charged. Then the oxygen reforms the double bond as the C -Cl bond is broken making a chloride ion. Finally, one hydrogen atom will break away from the nitrogen, remaking a neutral molecule and also a molecule of hydrochloric acid
