Amines Flashcards
What are the different mechanisms that amines can undergo
- nucleophilic substitution with halogen alkanes
- reduction of nitriles
- nucleophilic addition-elimination with acyl chlorides
What are the conditions for making nitriles?
KCN warm ethanolic aqueous, reflux
What does the base strength of an Amine depend on
- depend on how readily it will accept a proton H+
- how many akyls groups it has : these release electrons away from itself towards the nitrogen atom (inductive effect), increasing the electron density of the nitrogen atom = better electron pair donor so more attractive to protons
Why are aromatic amines weak bases?
because the benzene ring draws electrons towards itself and the nitrogen lone pair gets partially delocalised onto the ring, so the electron density on the nitrogen decreases,making the lone pair much availavle
Why are tertiary amines less strong bases than secondary amines
because they are less soluble in water due to nitrogen crowding
What are cationic surfactants?
Quaternary salts
have an ionic hydrophilic “head” and a long alkyl hydrophobic “tail” that dissolves greases
surfactants reduce the surface tension of liquids
positive nitrogen is attracted toward negatively charged surfaces such as glass and plastics
What are the uses of quaternary salts
fabric softener and surfactants
How do soaps destroy dirt?
they form micelles which surround the dirt/grease molecules, with the hydrophobic tails in the centre dissolving the grease and the hydphillic heads roundthe outside dissolving in the water
Why are nitriles reduced and what are the conditions of this?
to form amines
hydrogen gas and nickel catalyst (palladium and platinum also works) or LiAH4 in ethoxyethane
raised temperature and pressure
What are the conditions for mononitration (only one NO2 group added during electrophilic substitution)
keep temperature below 55 degrees
Why are nitro compounds useful?
can be used as explosives (e.g. TNT)
and used in the manufacture of dyes
How are primary aromatic amines prepared? Draw the equations
1) Electrophilic substitution : warm benzene with concentrated nitric and sulfuric acids to get nitro benzene
HNO3 + H2SO4 → H2NO3+ + HSO4-
H2NO3+ → NO2+ H2O
2) reduction of nitro compounds using tin and concentrated hydrochloric acid to form an ammonium salt. NaOH added to give the amine.
What are the two different methods for making aliphatic amines, which is the preferred method and why? Also mention the pros and cons
reducing nitriles - preferred but it is a two step reaction so there’s a low yield and KCN is toxic
reaction of ammonia with halogenalkanes
the halogenalkane reaction is not preferred because some of the primary amines can undergo further reactions to form secondary, tertiary amines and quaternary ammonium salts. can be minimised by excess ammonia
Write and draw the equation for making ethylamine by reacting ammonia and bromoethane
(making aliphatic amines with halogen alkanes)
:)
Write and draw the equations for making aliphatic amines by reducing nitriles? (mention why the different reactants are used)
Draw the mechanism for nucleophilic substitution when ethylamine reacts with a large excess of chloromethane (example of excess halogenalakanes)
Draw the mechanism when a large excess of propylamine reacts with chloromethane (example of excess amine). Name the product.
Draw the mechanism for the basic action of amine with water
What happens when amines react with acids. How are they regenerated back to amines. What happens when you react methylamine with HCL
all amines will react with acids to become ammonium salts. Addition of NaOH to an ammonium salt will convert it back
