Post on 19-Dec-2015
Amines – Amines contain a nitrogen atom that is bonded to
at least one carbon group– Can think of amines as derivatives of ammonia,
NH3
– aliphatic amine:aliphatic amine: all carbons bonded to nitrogen are derived from alkyl groups
– aromatic amine:aromatic amine: one or more of the groups bonded to nitrogen are aryl groups
CH3-NH2 CH3-N-CH3
H
CH3-N-CH3
CH3
Methylamine(a 1° amine)
Dimethylamine(a 2° amine)
Trimethylamine(a 3° amine)
Classification of Amines
– Amines are classified as 1°, 2°, or 3° depending on the number of carbon groups attached to nitrogen
– Aliphatic amine:Aliphatic amine: Only alkyl groups bonded to the nitrogen
– Aromatic amine:Aromatic amine: One or more aromatic (or aryl) groups bonded to the nitrogen
NH2 N-CH3
HCH2-N-CH3
CH3
Aniline(a 1° aromatic amine)
N-Methylaniline(a 2° aromatic amine)
Benzyldimethylamine(a 3° aliphatic amine)
Heterocyclic Amines– Heterocyclic amine:Heterocyclic amine: Amine in which the nitrogen
atom is part of a ring– Heterocyclic aliphatic amine:Heterocyclic aliphatic amine: Heterocyclic amine
in which the ring is saturated (has no C=C bonds) – Heterocyclic aromatic amine:Heterocyclic aromatic amine: Amine nitrogen is
part of an aromatic ring• Important in nature
PiperidinePyrrolidine Pyridine(heterocyclic aliphatic amines) (heterocyclic aromatic amines)
NH
NH
N N
N
Pyrimidine
N
N
Imidazole
N
N
N
N
HPurine
H
Common Names (easier)
• Aliphatic amines: List the groups bonded to nitrogen in alphabetical order followed by the suffix –amineamine
• Entire name given in one word
Diethylmethylaminesec-Butylamine
NNH2
NH2
Cyclohexylamine
NH2
Propylamine
IUPAC Nomenclature
• IUPAC names – IUPAC names for aliphatic amines derived in
similar way as alcohol names– Drop the final -e of the parent alkane and
replace it by -amine-amine– Use a number to locate the amino group on
the parent chain
CH3CHCH3
NH2
NH2
H2N NH2
1,6-HexanediamineCyclohexanamine2-Propanamine
IUPAC Nomenclature– Uses common name aniline for C6H5NH2, the
simplest aromatic amine– Use numbers to locate substituents OR– Use the prefixes ortho (o), meta (m), and para (p)– Several aniline derivatives have common names
that are still widely used
NH2
CH3
NH2
NO2
NH2
3-Methylaniline (m-Toluidine)
Aniline 4-Nitroaniline(p-Nitroaniline)
IUPAC Nomenclature– Name unsymmetrical secondary and tertiary
amines as N-substituted primary amines– Take the largest group bonded to nitrogen as the
parent amine– Name the smaller group(s) bonded to nitrogen– Show their location on nitrogen by using the
prefix N (indicating that they are bonded to nitrogen)
NCH3
CH3
NHCH3
N,N-Dimethyl- cyclopentanamine
N-Methylaniline
Ammonium salts
N is group 5
5 valence electrons
NH3 has an unshared pair
that can form a fourth bond
but with a + charge on N
Nomenclature of Amine Salts• Amine salts
– Have four atoms or groups of atoms bonded to a nitrogen atom i.e., CH3NH3
+ – Nitrogen bears a positive charge– Ion is a quaternary ion-4 bonds to N with + charge – Positive ion is associated with an anion as a salt– Compound named as a salt of the corresponding
amine• Replace the ending -amine-amine (or aniline or pyridine etc.) by
-ammonium-ammonium (or anilinium or pyridinium etc.)• Add the name of the anion (CH3CH2)3NH
+Cl-
Triethylammonium chloride
Physical Properties
• Small amines have very nasty, sharp, penetrating odors– Trimethylamine smells like rotting fish– Names sometimes reflect their odors:
• 1,4-butanediamine is putrescine • 1,5-pentanediamine is cadaverine
Physical Properties• Amines are polar compounds
– 1° and 2° amines have N-H bonds and can form hydrogen bonds with one another
– 3° amines have no N-H bond and cannot form hydrogen bonds with one another
Physical Properties– Hydrogen bonds between amines are weaker than
hydrogen bonds between alcohols, because O is more electronegative than N
– Boiling points of amines lower than those of comparable alcohols
– Boiling points of amines higher than those of comparable alkanes
– Compare ethane, methanamine and methanol:
CH3OHCH3CH3 CH3NH2
-6.3 65.032.031.1MW (amu)
bp (°C)
30.1
-88.6
Physical Properties
– Amines form hydrogen bonds with water and are more soluble in water than are hydrocarbons of comparable molecular weight
– Most small amines are completely soluble in water– Larger amines are only moderately soluble in
water or are insoluble
Basicity of Amines• Amines are weak bases
• Aqueous solutions of amines are basic– Acid-base reaction between an amine and
water involves transfer of a proton from water to the amine
CH3-NH
HH-O-H CH3-N-H
H
HO-H
Methylammoniumhydroxide
Methylamine(a base)
++
-: :
::
::
Base Conjugate acid
Reactions of Amines
• Basicity is most important chemical property of amines – Amines, whether soluble or insoluble in water,
react quantitatively with strong acids to form water-soluble salts
HO H
NH2HO
HOHCl
H2O
HO
HO NH3+Cl-
HHO
(R)-Norepinephrine hydrochloride(a water-soluble salt)
+
(R)-Norepinephrine(only slightly soluble in water)
Basicity of Amines
• Aliphatic amines– Weak base– Basicity similar to ammonia– Stronger than aromatic amines
• Aromatic or Heterocyclic aromatic amines– Very weak base– Weaker than aliphatic amines
C6H5NH2
CH3CH2NH2Aliphatic
Ammonia
Aromatic
3.0 - 4.0
4.74
8.5 - 9.5
Class pKb Example Name
Ethanamine
Aniline
Stronger base
Weaker base
Basicity of Amines
• Which form of an amine exists in blood?– pH of blood is approximately 7.40, which is slightly
basic– Thus an aliphatic amine dissolved in blood exists
predominantly in its protonated (conjugate acid) form
HO
HO
NH2
Dopamine
HO
HO
NH3+
Conjugate acid of dopamine(the major form present
in blood plasma)
Physical Properties of Quaternary Ammonium Salts
• Unlike 1o, 2o and 3o amines, quaternary nitrogens have 4 bonds and a +1 charge
• They are associated with an anion• Melting and Boiling points much higher than amines
(held together by charges)• Salts are much more soluble in water
– Many drugs are made as hydrochloride salts rather than just free amines
– Cocaine exists as “free base” or “crack” (smoked) and as HCl salt (injected)
Reactions of Amines
– example:example: complete each acid-base reaction and name the salt formed
(CH3CH2)2NH HCl
NCH3COOH
+(a)
(b) +
Reactions of Amines
– example:example: complete each acid-base reaction and name the salt formed
– solution:solution:
(CH3CH2)2NH HCl
NCH3COOH
NH
(CH3CH2)2NH2+Cl-
CH3COO-
Diethylammoniumchloride
+Pyridinium acetate
+(a)
(b) +
Alkaloids
• Alkaloids are basic compounds obtained from plants
• Alkaloids contain nitrogen
• Alkaloids frequently have physiological effects
• Alkaloids are often poisonous
• Common names often end in “ine”
Properties of Cocaine
Property Free Base
freebase/crack
HCl Salt
Melting point oC 98 195
Solubility in H2O Low high
Solubility in fats/oils
High none
Volatility High
Smoked
Low
Injected/inhaled
Related Alkaloids• Many compounds are related
– Heroin: H’s replaced by acetate– Codeine: Blue H replaced by methyl
• Codeine• Heroin • Demerol• Methadone
morphine
N
HO
O
HO
CH3