amines Flashcards
what are amines?
compounds based on ammonia
what is a primary amine?
when one of the hydrogens on the ammonia has been replaced by an alkyl group
what is a secondary amine?
when two of the hydrogens on the ammonia molecule have been replaced by alkyl groups
what is a tertiary amine?
when all three of the hydrogens on the ammonia have been replaced by alkyl groups
what is a quarternary ammonium compound?
formed from a tertiary amine where the lone pair on the hydrogen forms a coordinate bond to another alkyl group
why are small amines soluble?
they can form hydrogen bonds with water
how do small tertiary amines form h bonds with water?
the lone pair on the nitrogen forms h bond to the delta positive on the hydrogen on the oxygen
explain the relationship between solubility and length of hydrocarbon chain?
less soluble as hydrocarbon chain increases bc hydrocarbon chain has to force its way between water molecules
how can you make a primary amine?
halogenoalkane and ammonia
reduction with a nitrile
explain how primary amines can be made from halogenoalkanes
heat halogenoalkane and excess conc ammonia in ethanol in a sealed test tube
name the mechanism of the production of a primary amine from a halogenoalkane?
nucleophilic substitution
why can ammonia act as a nucleophile?
has a lone pair on the nitrogen
why does further substitution happen when a primary amine is made?
because the primary amine has a lone pair on the nitrogen so it can act as a nucleophile and react with the halogenoalkane
what is the major product when excess ammonia is used
primary amine
what is the major product when excess halogenoalkane is used?
quarternary amine
give some of the uses of quarternary ammonium salts
cationic surfactants which are found in detergents, fabric softeners and conditioners
give the reagents and conditions for the reduction of a nitrile to form an amine
ethanolic KCN
with hydrogen
nickel catalyst
OR a reducing agent eg. lithium tetrahydridoaluminate IN ETHER
give the equation of a nitrile being reduced
R-CN + 2H2 (or 4[H])—-> RCH2NH2
by what process is phenylamine made
reduction of nitrobenzene
give the equation of the reaction of nitrobenzene
RNO2 + 6[H] —-> RNH2 + 2H2O
give the conditions for the reduction of nitrobenzene
heat under reflux
in the presence of a tin catalyst
conc HCl
conc NaOH
why do you use a sealed test tube when making a primary amine?
so that the ammonia gas doesn’t escape
give the two stages of the reaction of ammonia with halogenoalkane
NH3 + R-X —> RNH3+X-
RNH3+X- + NH3 —-> RNH2 + NH4X
in the reduction of nitrobenzene, why is conc NaOH added?
because adding the acid gives the protonated form of the benzene. The NaOH removes the H+ to form water/
what are the uses of aromatic amines?
manufacture of dyes
what is a base?
a proton acceptor
why can ammonia and amines act as bases?
they have a lone pair on the nitrogen which can form a coordinate bond to protons
ammonia + acid —>
ammonium salt
amine + acid —->
alkyl ammonium salt
give an equation and explain how it shows that amines are weakly basic
RNH2 + H2O —-> RNH3+ + OH-
equilibrium lies to the left bc the amines only partially dissociate so the solution is only partially basic
what does the strength of a base depend on?
the availability of the lone pair
why are tertiary amines the strongest base?
because they have the most alkyl groups which have positive inductive effect so the lone pair is most available
why are aromatic amines the weakest base?
because the lone pair overlaps with the delocalised pi system so the lp is delocalised into it. the lp isnt readily available for
what is a disadvantage of using the nitrile method to make amines?
toxic KCN gas produced
what is a disadvantage of using the halogenoalkane method to make amines?
further substitution happens so more than one product so lower yield
how could you distinguish between samples of aqueous ammonia and amines?
use a pH meter
ammonia has a lower pH than amine
