Organic 11: Amines Flashcards
(40 cards)
What are amines derived from?
Ammonia
At least one hydrogen atom is replaced by an alkyl or aryl group
What is an alkyl group?
An alkane that has lost a hydrogen
E.g. a methyl group (CH3)
What is an aryl group?
An aromatic compound
Why are amines useful?
They are very reactive
So are commonly used as intermediates in organic synthesis
What is a primary amine?
An amine where one hydrogen is replaced by an alkyl or aryl group
What is a secondary amine?
An amine where two hydrogen atoms are replaced by alkyl or aryl groups
What is a tertiary amine?
An amine where all three hydrogens have been replaced by an alkyl or aryl group
What is the general formula for amines?
RNH2
Where R is an alkyl or aryl group
How do you name amines?
The prefix represents the alkyl or aryl group, and the suffix -amine represents the amine.
E.g. methylamine
Describe the shape of ammonia.
Pyramidal
Bond angle of 107
Why is the bond angle of ammonia different to that of a normal tetrahedron?
The lone pair of electrons on the nitrogen repels more than the bonding pair of electrons, reducing the bond angle.
Why are the boiling points of amines lower than the boiling points of their comparable alcohols (e.g. methyl amine and methanol)?
Primary amines can form hydrogen bonds to each other using their NH2 groups
Alcohols can form hydrogen bonds to each other using their OH groups
Nitrogen is less electronegative than oxygen so forms weaker hydrogen bonds
Which need less energy to break, so lower boiling point
What state are amines at room temperature?
Shorter chain amines (such as methyl and ethyl amine) are gases at room temperature
Longer chain amines are volatile liquids (rotting fish and rotting animal flesh smell of di- and triamines which are produced when proteins decompose)
Describe the solubility of amines.
Short chain amines (e.g. up to four carbon chain length) are very soluble in water and in alcohols because they form hydrogen bonds
Why are phenyl amines not soluble?
The benzene ring is not soluble as it cannot form hydrogen bonds as C-H bonds are non-polar
Hydrogen bonds also form more readily between molecules with polar groups like oxygen, fluorine or nitrogen
Why are amines so reactive?
Due to the lone pair on the nitrogen
It may be used to form a bond with a H+ ion when the amine acts as a base
Or form a bond with an electron-deficient carbon atom, when the amine is acting as a nucleophile
Why are amines classed as Bronsted-Lowry bases?
Because they can accept protons
How do amines react with acids?
Amines can react with acids to form salts
Describe and give an equation for the reaction of ethylamine with hydrochloric acid.
Ethylamine reacts with dilute hydrochloric acid to form ethyl ammonium chloride:
C2H5NH2 + H+ + Cl- –> [C2H5NH3]+ + Cl-
Ethyl ammonium chloride is an ionic compound that will crystallise as the water evaporates
Describe how phenylamine reacts with hydrochloric acid.
Dissolves in excess hydrochloric acid
Forms soluble ionic salt: phenyl ammonium chloride
How would you regenerate phenylamine from phenyl ammonium chloride?
Add a very strong base like sodium hydroxide
This removes the proton from the salt and regenerates the insoluble amine
As well as water and a chloride ion
Give the order of base strength for amines.
Tertiary amine > Secondary amine > Primary amine > Ammonia > Aromatic amines
Why are primary alkylamines stronger bases than ammonia?
An inductive effect is created as the alkyl groups release their electrons towards the nitrogen atom, increasing the electron density on the nitrogen atom, which makes it more attractive to protons
So acts as a better proton acceptor (base)
Why are secondary alkylamines stronger bases than primary alkylamines and ammonia?
They have twice as many inductive effects due to the two alkyl groups so have greater electron density on the nitrogen
So it will be a better proton acceptor
