Alkaloids are amines produced by plants'

1

2

3

Alkaloids are amines produced by
plants. Alkaloids taste bitter, and have
significant physiological effects. Many alkaloids
are used for medicinal or other physiological
purposes.
4

• Amines and amides are derivatives of ammonia in
  which one or more hydrogen atoms have been
  replaced by organic groups. The organic groups
  can be aliphatic, aromatic, or both.

• The hybridization about the nitrogen atom in
  singly bonded amines or amides is sp3 or
  tetrahedral.
• Three of the four tetrahedral positions involve
  bonds to hydrogen atoms or organic groups,
  however, the fourth position is occupied by a
  pair of non-bonding electrons (lone pair).
• The bond angles about the nitrogen atom in amines
  is about 109.5, however, in amides it is close
  to 120

5

Amines are classified as primary (1), secondary
(2), and tertiary (3).
Amines are also classified as aromatic (aryl) or
aliphatic amines. Aromatic amine at least one
benzene or other aromatic group is directly
bonded to nitrogen. Aliphatic amine no benzene
or other aromatic group is directly bonded to
nitrogen.
6

7

8

C6H5NH2 is called aniline. Substituted anilines
are named as derivatives of aniline. The prefix
N- is used to distinguish substituents directly
attached to the nitrogen atom from those attached
to the aromatic ring.
Many amines have disagreeable odors the smell of
rotting meat is due to Putrescine
(1,4-butanediamine) Cadaverine (1,5-pentanediamine
)
9

10

11

The physical properties of amines depend upon
whether they are primary, secondary, or
tertiary. Primary and secondary amines have
melting and boiling points comparable to those of
aldehydes and ketones. Tertiary amines have
melting and boiling points considerably lower
than those of primary and secondary amines,
comparable to those of ethers and hydrocarbons.
12

Tertiary amines do not possess an N-H bond and
therefore exhibit only weak secondary forces.
Primary amines contain two N-H bonds secondary
amines contain only one N-H bond. Both exhibit
strong secondary forces (hydrogen bonding),
primary amines slightly more so than secondary
amines.
Three- or four-carbon amines are soluble in water
in all proportions. Solubility drops off until it
becomes very low for amines with more than six or
seven carbons. Tertiary amines are slightly less
soluble than primary or secondary amines. The
water solubility of amines is about the same as
for aldehydes and ketones.
13

In aqueous solutions, (alkyl)amines react with to
form (alkyl)ammonium ions and hydroxide ions
The equilibrium of this reaction lies far to the
left only about 6 of the amine has reacted at
equilibrium.
Amines are more basic than water, but less basic
than strong bases, such as sodium hydroxide.
14

The reaction of an amine with a strong acid such
as HCl goes to completion the amine is converted
into an amine salt.
The amine is often called the free amine or free
base to distinguish it from the amine salt. In
the body, at physiological pH (7) amines are
almost entirely (gt99) in their amine salt form.
15

16

Amine salts are named by naming the positive ion
first and then naming the negative ion.
17

Properties of Amine Salts

• The melting and boiling points of amine salts are
  much higher than those of the corresponding
  amines.
• All amine salts are solids at room temperature.
• Methylammonium chloride MP 232C, BP decomposes
• Methylamine MP -94C, BP -6C
• Amine salts are much more soluble in water than
  amines due to the strong interaction of water
  molecules with ions.
• Amines used as medicines are almost always used
  in their salt form
• Amines undergo air oxidation resulting in a short
  shelf life.
• Water solubility is required for intravenous
  injection.

18

Quaternary Ammonium Salts
Quaternary ammonium salts contain four alkyl or
aryl groups attached to a central nitrogen atom.
Quaternary ammonium salts in which one of the
alkyl groups is a long hydrocarbon chain (such as
CH3 (CH2) 17-) are used as soaps, germicides,
antiseptic soaps, and mouthwashes. They are used
for disinfecting skin and hands prior to surgery
and for sterilizing surgical instruments. Choline
is a quaternary ammonium salt that is a
component of biological membranes and sometimes
functions as a neuraltransmitter.
19

20

Amides contain a carbonyl group attached directly
to a nitrogen. They may be classified as primary,
secondary, and tertiary
R1, R2, and R3 can be aliphatic or aromatic.
21

The synthesis of an amide involves the reaction
of a carboxylic acid with ammonia or a primary or
secondary amine. At room temperature, an
acid-base reaction occurs instead of the expected
condensation reaction.
But, at elevated temperatures (gt100C) the two
reactants condense to form an amide
22

The reaction to form an amide is very similar to
esterification. In both reactions a carboxylic
acid undergoes substitution with dehydration
between the carboxylic acid and the other
reagent. Amide formation is reversible. Removal
of water shifts the equilibrium towards the side
of amide formation. Water is removed by running
the reaction at a higher temperature than the
boiling point of water. Tertiary amides cannot
form amides, since they do not contain an N-H
bond. Tertiary amides do undergo an acid-base
reaction with carboxylic acids. Amide formation
is an acyl transfer reaction, with the carboxylic
acid acting as an acyl transfer agent.
23

Polyamides are produced by the polymerization of
bifunctional reagents (like polyesters). In
polyamides the reagent monomers are usually
diamines and dicarboxylic acids
The most important biological polyamides are
polypeptides and proteins.
The polymerization reaction between
1,6-hexanediamine and hexanedioic acid produces
poly(hexamethylene adipamide), or nylon 66
24

25

Three important observations concerning the
physical properties of amides
Amides have the strongest secondary attractive
forces and the highest melting and boiling points
of any covalent organic compounds.
26

The amide structure is best represented as a
resonance hybrid of the following structures
The structure on the right is called a dipolar
ion because atoms bearing opposite charges exist
on the same molecule. The large charge separation
in an amide molecule results in unusually large
polarity and secondary attractive forces. Because
the bond between the carbonyl carbon atom and the
nitrogen atom has a partial double bond
character, the bond angles around the carbonyl
carbon atom and nitrogen atom are both close to
120 (sp2 hybridization).
Amides are only slightly more soluble than
carboxylic acids. Amides are not more basic than
water, ethers, or alcohols.
27

Hydrolysis of amides occurs less readily than the
hydrolysis of esters, especially at neutral pH.
This property is of utmost importance in
biological systems for the stability of proteins.
In acidic and basic hydrolysis of amides, one of
the products is converted into a salt, which
drives the equilibrium to the right.
The acid or base used to hydrolyze an amide is
not a catalyst. It is consumed in the reaction
and is required in equimolar amounts relative to
the amide. The hydrolysis and synthesis of amide
bonds occur continuously in living systems. These
reactions are carried out using enzyme catalysts.
28