Amines Flashcards
what are amines? (2)
weak bases (Bronsted-Lowry)
nucleophiles
how can primary amines be prepared?
by the reaction of ammonia with halogenoalkanes (nucleophilic substitution) and by the reduction of nitriles (hydrogenation)
how are aromatic amines prepared?
by the reduction of nitrobenzene
what are aromatic amines used in?
the manufacture of dyes
what reactions do amines undergo?
nucleophilic substitution
nucleophilic addition-elimination
what happens to ammonia for an amine to be produced?
at least one hydrogen is replaced by an organic group
(amines are derivatives of ammonia)
in the nucleophilic substitution reaction to produce amines, how can only a primary amine be produced?
by adding ammonia in excess
how can the products be separated in the nucleophilic substitution reaction to produce amines?
fractional distillation
what conditions are needed for the reduction of nitriles?
LiAlH4 (reducing agent)
acidic conditions
what conditions are needed for the reduction of nitrobenzene?
Sn (Tin) - catalyst
conc. HCl
what are cationic surfactants?
molecules with a positive and negative end
why are cationic surfactants good conditioners?
the 2 oppositely charged ends are attracted to different substances which prevents static from building up on surfaces
why are amines bases?
the lone electron pair can accept protons
what does the strength of an amine as a base depend on?
the availability of the lone pair
more available = more likely to accept a proton = stronger base
how can different functional groups affect how available a lone pair is?
by changing the electron density around the bond
what is a negative inductive effect?
draws electron density away = lone pair less available
what is a positive inductive effect?
pushes electron density in = lone pair more available
which are stronger bases, aliphatic amines or aromatic amines?
aliphatic amines
are amines reactive?
yes they are very reactive
what is the name of CH3–NH2?
methylamine
what is the name of C2H5–NH2?
ethylamine
what is the name of NH2 with a benzene ring?
phenyl amine
what can the R be in RNH2 (amines)?
an alkyl group or an aryl group (aromatic)
are the boiling points higher or lower of amines with comparable alcohols (e.g. methylamine and methanol)? why?
alcohols have higher boiling points because the O-H bond is more polar so the hydrogen bonds are stronger and so require more energy to overcome
are amines polar or non-polar?
polar
what do amines react with acids to form?
salts (ionic compounds)
which are stronger bases, ammonia or primary alkyl amines?
primary alkyl amines
which are stronger bases, primary alkyl amines or secondary alkyl amines? why?
secondary alkyl amines because they have two inductive effects (from the 2 alkyl groups)
what do alkyl groups do in an amine?
release electrons away from the alkyl groups towards the nitrogen atom (positive inductive effect)
what do aryl groups do in an amine?
withdraw electrons from the nitrogen atom (negative inductive effect)
why is the preparation of amines through the reaction of ammonia with halogenoalkanes not efficient?
because a mixture of products is produced (1, 2, 3 amine and a quaternary ammonium salt)
