Download 102 Lecture Ch19

Structure and Classification of Amines
• Amines are derivatives of ammonia, the same way that
alcohols are derivatives of water
• Amines have a nitrogen, with hydrogens and/or alkyl
groups attached
• The shape around the nitrogen is pyrimidal and there is a
lone pair of electrons on the nitrogen
• Amines can be classified as 1º, 2º or 3º, just like carbons,
based on how many alkyl groups are attached to the
nitrogen
H
N
H
H
Ammonia
NH2
Primary Amine
H
N
N
Secondary Amine
Tertiary Amine
Naming Amines
• Most simple amines are named by their common names
(which are accepted by IUPAC)
• For common names, the alkyl groups attached to the N are
named alphabetically, and amine is added to the end
• IUPAC rules are more often used for more complicated
amines
- find the longest chain bonded to N, and replace -e in
alkane name with amine
- number at end nearest N and give number for position of N
- the prefixes di, tri etc. are used for multiple amines
- when amines are with other functional groups they are
called amino groups
NH2
N
NH2
O
H
N
NH2
H
trimethylamine
ethylmethylamine
2-butanamine
3-aminobutanal
H 2N
1,2-ethanediamine
Naming Aromatic and Heterocyclic Amines
• Aromatic amines are named as analines
• When alkyl groups are attached to the aromatic N, they are
written as N-alkyl at the beginning of the name
• As substituents on the ring they are named as amino groups
• Heterocyclic amines have one or more nitrogens as part of
the ring and are usually named by their common names
- know those that are boxed
NH2
H
N
NH2
OH
O
N-methylanaline
analine
ortho-aminobenzoic acid
N
N
N
N
N
H
N
H
N
H
N
H
N
N
pyrrolidine
pyrrole
imidazole
piperidine
pyridine
pyrimidine
N
purine
N
H
Physical Properties of Amines
• Primary and secondary amines can H-bond with
themselves, so have relatively high boiling points
• However, because the N-H bond is less polar than the O-H
bond, amines have lower boiling points than alcohols
• Primary and secondary amines have boiling points similar
to aldehydes and ketones
• Tertiary amines can’t H-bond with themselves, and so have
boiling points near those of ethers and hydrocarbons
• Smaller amines (less than 5 carbons) are soluble in water
- primary and secondary amines are more soluble than
tertiary because they have more H-bonding with water
Basicity of Amines and Amine Salts
• Amines are weak bases that partially ionize in water to
form ammonium ions and hydroxide ions
• When treated with acids, amines form salts, without the
formation of water
• Quaternary ammonium ions have 4 alkyl groups attached
to the nitrogen, and have a permanent positive charge on
the N (no H attached to N, so can’t react with bases)
• Amine salts are solids at room temperature and are soluble
in water, making them much more useful as medicines
NH2
+
H2O
+
NH3
H
N
+
HCl
N
Cl
OH
Alkaloids
• Alkaloids are naturally occurring compounds that contain
nitrogen and have basic properties
• They have a wide variety of structures, including simple
amines, aromatic amines, and heterocyclic amines
• Some examples of alkaloids are caffeine and the opiates
Structure and Naming of Amides
•
•
•
•
•
•
Amides are considered derivatives of carboxylic acids
They have an amino group attached to the carbonyl
Most simple amides are known by their common names
For common names the -ic acid is changed to -amide
For IUPAC names the -oic acid is changed to -amide
Alkyl groups attached to the amide nitrogen are indicated
by writing N-alkyl or N,N-dialkyl before the amide name
O
O
O
H
O
NH2
NH2
OH
methanamide
(formamide)
ethanamide
(acetamide)
NH2
N
H
N-methyl-2-hydroxybutanamide
Br
para-bromobenzamide
Physical Properties and Stability of Amides
• Primary and secondary amides can H-bond with themselves,
and so have high melting and boiling points
• Tertiary amides can’t H-bond with themselves, so have lower
melting and boiling points than primary or secondary
• Amides have higher melting and boiling points than carboxylic
acids because they are more flat (due to delocalization of
electrons), so they stack better
• Amides (except formamide) are solids at room temperature
• Smaller amides (5 carbons or less) are soluble in water
• Unlike amines, amides are not basic
• They are also very stable (unreactive) compared to esters
• This is due to the delocalization of the nonbonded pair of
electrons (through resonance)
O
O
NH2
O
NH2
NH
Preparation of Amides from Carboxylic Acids
• Amines (except tertiary) can react with carboxylic acids to
produce amides (amidation)
• The reaction is similar to esterification
• Unfortunately, the reaction is of little synthetic use
- amines are bases and will remove a proton from a
carboxylic acid, making the acid carbonyl unreactive
- primary amides can be formed using ammonia this way,
but yields are not great
- amides are generally prepared by other methods
O
O
+
OH
NH3
heat
+
NH2
H2O
Hydrolysis of Amides
• Amides can be hydrolyzed to carboxylic acids using either
acid or base, similar to the hydrolysis of esters
• However, amides are much more resistant to hydrolysis
than esters, which is what makes proteins so stable
• In the stomach, hydrolysis of amide bonds in proteins is
facilitated by enzyme catalysts
• Amide bonds are much more common in medicines than
esters due to this resistance to acid-catalyzed hydrolysis
(the drugs are more likely to make it through the stomach)
O
HCl
O
+
NH2
H2O
O
NH4
Cl
OH
O
NaOH
NH2
+
O
Na
NH3