Difference between primary secondary and tertiary amines
Primary amines have one R group attached to the nitrogen atom
Secondary amines have two R groups attached to the nitrogen atom
Tertiary amines have 3 R groups attached to the nitrogen atom
What is the general formula of primary amines and how are they named
RNH2 - R can be an alkyl or an aryl group
e.g CH3- NH2 is methylamine
Describe the solubility of primary amines
With chain lengths of up to about 4 carbon atoms they are very soluble in water and alcohols as they can form hydrogen bonds with these solvents
Most amines are also soluble in less polar solvents
Describe the differences in bp between primary amines and regular alkanes
Both molecules have the same number of electrons and have similar shapes-
Methylamines have a much higher bp
This is because PA can form hydrogen bonds with eachother aswell as van deer waals and dipole dipole interactions
How does the bp of primary amines change
Inc chain length= inc bp of primary amines
Greater number of van deer waals, more electrons, more temporary dipoles, more induced dipoles
Describe hydrogen bonding in secondary amines
Weaker hydrogen bonds- less frequent
-Nitrogen atom is in the middle of the chain rather than at the end of the chain makes the permanent dipole lesser
Why do primary amines have higher bp than secondary amines
-Secondary amines have lower dipole dipole interactions compared with primary amines
Describe bonding in tertiary amines
- No hydrogens attached directly to the nitrogen atom
- This means T-A dont have hydrogen bonding
- This means bp is much lower than S-A and P-A
Simple- how are amines made using halogenoalkanes
Halogenoalkane heaated in a concentrated solution of ammonia in ethanol, reaction is carried out in a sealed tube
Not made in reflux
How does the role of ammonia change throughout the preparation of primary amines from halogenoalkanes
1st stage it acts as a nucleophile-attacks the electron deficient carbon atom
2nd stage it acts as a base-ammonia may remove one of the hydrogens on the NH3+
How do further reactions form secondary amines
-The primary amine formed in the substitution reaction has a lone pair on the nitrogen and will react futher with the halogenoalkane
What is used in a reaction to promote the formation of a quaternary salt?
Excess of halogenoalkane
Describe the reaction scheme for the gradual formation of amines via substitution by halogenoalkanes
Using an excess amount of ammonia maximises the amount of primary amine formed
Using an excess of halogeoalkane will promote the formation of the quaternary salt
How are quaternary ammonium salts used as catonic surfactants
Surfactants reduce the surface tension of liquids
Positive nitrogen is attracted towards negatively charged surfaces such as glass and hair
Helps use in fabric softeners , hair conditioners and sewage flocculants
Why is preparing amines from nitriles more efficient than nucleophilic substitution
Nucleophilic substitution does not prepare a high yield of primary amine due to the further substitution reactions that occur
Describe the 2 step reaction scheme of preparing amines from nitriles
Step 1- Convert halogenoalkane to nitrile by using KCN in aqueous ethanol ( heat under reflux)
CH3CH2Br + CN- = CH3CH2CN + Br-
Step 2- Reduce nitrile to amine by using LiAlH4 in ether or by reducing with H2 using a Ni catalyst
CH3CH2CN + 4(H)= CH3CH2CH2NH2
Give the disadvantage of the 2 step method
- May have a low yield as it is a two step reaction
- KCN is also toxic
How can amides form using acycl chlorides in a nucleophilic addition- elimination reaction
FG, Reagent, Conditions-
Functional group changes from acyl chloride- secondary amide
Reagent- primary amine
Conditions- room temp
Equation for the formation of amides friom acyl chlorides and primary amine
-RCOCl +2CH3NH2 = RCONHCH3 + CH3NH3+Cl-
How can amides be formed using acid anhydride in a nucleophilic addition elimination reaction
FG, Reagent, Conditions-
Functional group changes from an acid anhydride= secondary amide
Reagent- primary amine
Conditions- room temp
Equation for the formation of amides using acid anhydride in a nucleophilic elimination addition reaction
(RCO)2O +2CH3NH2 =RCONHCH3+ [CH3NH3] [RCO2]-
Describe the base strength of primary aliphatic amines
- They have a lone pair of electrons on the nitrogen which is readily available for forming a daitive covalent bond with a H+ and so accepting a proton
- Weak bases because only a low conc of hydroxide ions are produced
Bronsted lowry bases
Describe the differences in base strength of primary aliphatic amines and ammonia
For primary aliphatic amines-
The alklyl groups are electron releasing and push the electrons away from themselves towards the nitrogen atom
This increases the negative charge on the nitrogen atom which makes the lone pair of electrons on the nitrogen atom more readily available to accept protons
This means the lone pair on the nitrogen for primary aliphatic amines have a stronger ability to pick up a hydrogen ion( proton) as it is a stronger base
Describe the base strength of secondary amines in comparison to primary aliphatic amines and ammonia
- Stronger bases than primary aliphatic amines because they have more alkyl groups that are substituted on to the N atom in place of the H atoms
-This means more electron density is pushed on to the N atom ( greater inductive effect) so making the lone pair on the N atom more readily available
