Topic 18 - Organics 3 Flashcards
(35 cards)
What is the functional group of amines?
-NR2 where R is an alkyl group or H
What does aliphatic mean?
A term for compounds without any benzene ring structures
What happens if the nitrogen atom in an amine is bonded to four alkyl groups?
You would get a positively charged quaternary ammonium ion
How are aliphatic amines made from halogenoalkanes?
By heating the halogenoalkane with an excess of ethanolic ammonia
How are aliphatic amines formed by reducing a nitrile?
By warming with LiAlH4 in dry ether then adding dilute acid
Negatives of forming amines from halogenoalkanes and why?
Get a mixture of primary, secondary and tertiary amines. As amines can act as a nucleophile due to its lone pair, meaning they can take part in nucleophilic substitution reactions with any halogenoalkanes
What are the negatives of forming amines from reducing amides?
LiAlH4 is too expensive for industries to use, therefore in industries they use catalytic hydrogenation
What is catalytic hydrogenation?
When nitriles are reduced using H2 gas with a metal catalyst ( platinum or nickel), at high temperature and pressure
How are aromatic amines formed by reducing a nitro compound in the first step of making a salt?
By heating a mixture of a nitro compound, tin metal and concentrated hydrochloric acid under reflux
How are aromatic amines formed by reducing a nitro compound in the second step?
By the addition of sodium hydroxide the salt can be de-protonated and then distilled off
Why can amines form weak bases?
Due to their lone pair on the nitrogen atom that can form dative bonds with hydrogen ions
What does the strength of amines as bases depend on?
On how available the nitrogen’s lone pair is. The more available it is the more likely the amine is to accept a proton so will be a stronger base
Why are primary aromatic amines weaker bases than ammonia?
The benzene ring causes the lone pair to get partially delocalised onto the ring, decreasing the electron density of the nitrogen, making the lone pair much less available
Why are primary aliphatic amines stronger bases than ammonia?
The alkyl groups push electrons onto the attached groups, increasing the electron density of the nitrogen, making the lone pair more available
Why are small amines soluble in water?
Amine group can form hydrogen bonds with water molecules
What is the reaction of amines as bases and how can it be reversed?
The amine reacts with acid to form a salt.
This can be reversed by adding a strong base (e.g. hydroxide)
What happens when small amines dissolve in water?
They form alkaline solutions
Why are big amines less soluble in water?
They have greater london fotces between molecules and the chains disrupt the hydrogen bonding
How can primary amines be turned into secondary and tertiary amines?
Primary amines are nucleophiles, therefore they can react with halogenoalkanes in nucleophilic substitution to form salts of secondary and tertiary amines
How can salts be easily deprotonated?
By adding a strong alkali like sodium hydroxide
When amines are reacted with acyl chlorides what does it form?
N-substituted amide and hydrochloric acid
How are N-substituted amides formed from amines?
A H atom is swapped for the acyl group, RCO
How do you detect that hydrochloric acid is present?
Steamy fumes, turns damp blue litmus paper red
What is the functional group of amides?
-CONH2
