CHAPTER 10: AMINES

AMINES

Nitrogen containing compound Nitrogen is a group 5A element with 5

valence electrons Nitrogen has 3 bonds and 1 lone pair Ammonia derivatives where at least one H is

replaced by an alkyl, cycloalkyl, or aryl group

• Amines are organic nitrogen compounds, formed by replacing one or more hydrogen atoms of ammonia (NH3) with alkyl groups.

• Amines are classified as 10, 20, or 30 based on the number of alkyl groups bonded to the nitrogen atom.

Structure and Bonding• An amine N atom is sp3 hybridized and trigonal pyramidal, with

bond angles of approximately 109.50.

• Since an amine nitrogen has four different groups around it, it is technically a stereocenter.

Amines

Structure and Bonding• However, the chirality of the amine nitrogen can be ignored

because the two enantiomers interconvert by passing through a trigonal planar (achiral) transition state.

Amines

Structure and Bonding• In contrast, the chirality of a quaternary ammonium salt with four

different groups cannot be ignored. Because there is no nonbonded electron pair on the nitrogen atom, interconversion cannot occur, and the N atom is just like a carbon atom with four different groups around it.

Amines

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STRUCTURE OF AMINES

Aliphatic aminesN bonded to alkyl groupsAromatic AminesN bonded to one or more aryl groups

NH2N CH3CH3NHCH2CH3

CH3

|

CH3CH2NCH3

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HETEROCYCLIC AMINES Heterocyclic aliphatic

amines Ring is saturated and

N is part of a non aromatic ring

Heterocyclic aromatic amines When nitrogen is part

of an aromatic ring

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N

NN

N

N

H

N

H

N

H

Pyrrolidine Pyrrole

Piperidine Pyridine Pyrimidine

N

N

N

N

H

Purine

N

H

Imidazole

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NAMING AMINES

Amines may be named using either common or IUPAC rules

For common names, list the alkyl groups attached to the N in ABC order and use the suffix –amine, which is written as one word

Prefixes di- and tri- are used if identical groups are present

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IUPAC NAMING OF 1O AMINES

1. Select the longest carbon chain that contains the N as the parent

2. Name parent as an alkan-amine by removing the –e of the alkane and replacing it with the suffix –amine

3. # the parent from the end nearest the N4. The location of the amino group comes before

the parent5. If the parent is substituted, its name and #

comes before the parent

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NOMENCLATURE

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IUPAC NAMING 1O AMINES

Compounds with 2 amino groups are named by adding suffix -diamine. The final ‘e’ of the parent hydrocarbon is retained

H2NCH2CH2CH2CH2CH2CH2NH2

1,6-hexanediamine

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3

N H2

|

CH CHCH2NH2

1,2- propanediamine

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IUPAC NAMING 2O AND 3O AMINES

1. 2o and 3o amines are named as N-substituted primary amines

2. The largest alkyl chain is considered the parent3. The other alkyl chains are placed in front of the

parent using the prefix N- to denoted that it is attached to the N

CH3NHCH2CH3

N- methylethanamine N(CH3)2

N,N-dimethylcyclohexanamine

HN—CH3

|CH3—CH2—CH2—NH—CH3 CH3—CH—CH2—CH3

3 2 1 1 2 3

4

N-Methyl-1-propanamine N-Methyl-2-butanamine

( d

3CH — NH — CH

3

N - methylmethanamine

imethylamine )

AnilineN - methylaniline

NH2 NH CH3

If other functional groups are present on an amine, the –NH2 group is a substituent and is called –amino

Priority List from highest to lowest:carboxylic acid, aldehyde, ketone,

alcohol, amine

NOMENCLATURE PRIORITY

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Learning Check

Give the name and classify:

A. CH3NHCH2CH3

B.

CH3

|

CH3CH2NCH3

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20

Solution

A. CH3NHCH2CH3

N-methylethanamine , 2°

CH3|

B. CH3CH2NCH3

N,N- dimethylethanamine , 3°

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Solution

A. 1-pentanamine

CH CH CH CH CH -NH3 2 2 2 2 2

B. 1,3-cyclohexanediamine

NH2

NH2 21

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PHYSICAL PROPERTIES

• Amines are polar compounds• Both 1° and 2° amines form hydrogen bonds• Boiling points are higher than corresponding alkanes

but lower than the corresponding alcohols• Are soluble if 6 or less carbons are present

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BOILING POINTS

N-H less polar than O-H. Weaker hydrogen bonding. Tertiary amines cannot hydrogen bond.

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PHYSICAL PROPERTIES OF AMINES

Compound Formula Mass BP(oC)

CH3CH3 30 -89

CH3NH2 31 -6

CH3OH 32 65

Boiling points of amines are higher than those of alkanes but lower than those of alcohols

BASICITY OF AMINES

Lone pair of electrons on nitrogen can accept a proton from an acid

All amines are weak bases and aqueous solutions of amines are basic

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Methyl-ammonium ion

Methylamine

++

••

••

•• -

••

••

••

H H

C H3

- N H- O - H C H3

- N - H O - H+

Hydroxide ion

Interesting and Useful Amines• Many low molecular weight amines have foul odors.• Trimethylamine [(CH3)3N], formed when enzymes break

down certain fish proteins, has the characteristic odor of rotting fish.

• Putrescine (NH2CH2CH2CH2CH2NH2) and cadaverine (NH2CH2CH2CH2CH2CH2NH2) are both poisonous diamines with putrid odors. They too are present in rotting fish, and are partly responsible for the odors of semen, urine, and bad breath.

• Naturally occurring amines derived from plant sources are called alkaloids.

Amines

Interesting and Useful Amines• Histamine, a rather simple triamine that is

present in many tissues, is responsible for a wide variety of physiological effects.

• Understanding the physiological properties of histamine has helped chemists design drugs tocounteract some of its undesirable effects. Antihistamines bind to the same active site as histamine in the cell, but they evoke a different response. Examples are brompheniramine and cimetidine.

Amines

Interesting and Useful Amines• A large number of physiologically active compounds are derived from

2-phenethylamine (C6H5CH2CH2NH2). These compounds include adrenaline, noradrenaline, methamphetamine, and mescaline. Each contains a benzene ring bonded to a two-carbon unit with a nitrogen atom (shown in red).

Amines

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NEUROTRANSMITTERS

Neurotransmitter – chemical substance that is released at the end of a nerve, travels across the synaptic gap, and then bonds to a receptor site on another nerve, causing a nerve impulse

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HO

HO

NH2

OH

HO

HO

NH2

HO

HO

HN

OH

N

N

H

NH2

Norepinephrine Dopamine

Epinephrine Histamine

• Three natural dyes known for centuries are indigo, tyrian purple, and alizarin.

Natural and Synthetic Dyes

Amines

• In 1935, Gerhard Domagk first used a synthetic dye, prontosil, to kill bacteria.• Prontosil and other sulfur containing antibiotics are collectively known as sulfa

drugs.• Prontosil is not the active ingredient itself—In cells, it is metabolized to

sulfanilamide, the active drug.

Sulfa Drugs

Amines

• To understand how sulfanilamide functions as an antibacterial agent, we must examine folic acid, which microorganisms synthesize from p-aminobenzoic acid.

Sulfa Drugs

• Sulfanilamide and p-aminobenzoic acid are similar in size and shape and have related functional groups.

Amines

• When sulfanilamide is administered, bacteria attempt to use it in place of p-aminobenzoic acid to synthesize folic acid. Derailing folic acid synthesis means that the bacteria cannot grow and reproduce. Sulfanilamide only affects bacterial cells, because humans do not synthesize folic acid, and must obtain it from their diets.

Sulfa Drugs

Amines