CH 23 - Amines

amines are derivatives of ammonia where

one or more hydrogens are replaced with organic groups

amines are classified as primary, secondary, and tertiary depending on

number of carbons bonded to the nitrogen

when nitrogen is part of a ring, these are referred to as

“heterocycles” or “heterocyclic amines”

aliphatic amines - suffix

-e of parent alkane is replace with -amine

anilines

amino groups bonded to a benzene ring

2* and 3* amines are names as

N-substituented 1* amines (largest group is parent amine)

amines have low priority compared to tother functional groups, in this case, named as

an amino substituent

where four groups bonded to nitrogen - formal + charge on

nitrogen

where four groups bonded to nitrogen - name of salt uses name of

corresponding amine with the ending -ium

where four groups bonded to nitrogen - if four alkyl/aryl groups, these these are

quaternary (4*) ammonium ions

four different groups (including a lone pair) around a sp3 nitrogen produces

a chiral center

chirality of amines - in most cases, these cannot be separated because the

enantiomers rapidly interconvert at room temperature by “pyramidal inversion”

chiral 4* ammonium ions do not

undergo pyramidal inversion

amines are

polar compounds (polar C-N bonds)

1* and 2* amines can form

hydrogen bonds

• but weaker than O-H bonds

all amines can form hydrogen bonds with

protic solvents like water

amines are also

weak bases

• pKa of conjugate acid ~ 10

the conjugate acids of anilines on aromatic heterocyclic amines are

stronger acids

• parents are weaker bases

all amines (water soluble or not) react with strong acids to form

water-soluble ammonium salts

preparation of amines - alkylation = treatment of ammonia or an amine with alkyl halide gives a

alkyl ammonium salt (Sn2 mechanism)

preparation of amines - alkylation = mixtures often result as any excess ammonia can

deprotonate ammonium salt product

preparation of amines - alkylation of azide = treatment of azide anions with an alkyl halides gives a

alkylazide

• replace Cl with N3

• then reduce to get NH2

azide can also open

epoxides

preparation of amines also

• reductive amination of aldehydes/ketones

• reduction of amides with LiAlH4

• reduction of nitrobenzenes

reaction with nitrous acid (HNO2) forms

diazonium ions (RN2+) with 1* amines

• N2 is LG

reaction with nitrous acid (HNO2) - aromatic diazonium ins can be converted

into a number of functional groups

• lose N2 then use reagent on what desired product needed

Hofmann elimination - when treated with a strong base, 4* ammonium salts undergo rapid

E2 eliminations to make less substituted (non-Zaitsev alkenes)