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15.1 Amines15.2 Naming Amines15.3 Physical Properties of Amines

Chapter 15 Amines

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Amines are organic compounds in which one or more H in ammonia, NH3, is replaced with alkyl or aromatic groups.

H H H| | |

H—N—H CH3—N—H CH3—N—CH3

ammonia

Amines

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Classification of AminesAmines are classified as primary, secondary, or tertiary.In a primary (1°) amine, one carbon group is bonded to the nitrogen atom.A secondary (2°) amine has two carbon groups.A tertiary (3°) amine has three carbon groups.

H CH3 CH3| | |

CH3—N—H CH3—N—H CH3—N—CH3

1° 2° 3°

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Models of Amines

The three-dimensional models show the shapes of amine molecules with one or more alkyl groups bonded to the nitrogen atom.

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Simple amines are named as alkylamines.The alkyl groups bonded to the N atom are listed in alphabetical order in front of amine.CH3—CH2—NH2 CH3—NH—CH3Ethylamine Dimethylamine

CH3|

CH3—N—CH2—CH3 Ethyldimethylamine

Common Names of Amines

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In the IUPAC system, amines are named as alkanamines. The –e in the alkane name of the longest chain is changed to –amine.The chain is numbered to locate the amine group and substituents.

NH2|

CH3—CH2—NH2 CH3—CH—CH3Ethanamine 2-Propanamine

IUPAC Names of Amines

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Each alkyl groups bonded to the N atom is named as N-alkyl groups in front of the amine name for the longest chain.

HN—CH3|

CH3—CH2—CH2—NH—CH3 CH3—CH—CH2—CH3

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

Naming Secondary and Tertiary Amines

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Give the common and IUPAC names and classify as primary, secondary, or tertiary:A. CH3—CH2—CH2—NH2

CH3|

B. CH3—CH2—N—CH3

Learning Check

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A. CH3—CH2—CH2—NH2

1-propylamine, 1-propanamine, 1°

CH3|

B. CH3—CH2—N—CH3

ethyldimethylamine, N,N-dimethylethanamine, 3°

Solution

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Write a structural formula forA. 2-pentanamine

B. N-methyl-1-butanamine

Learning Check

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A. 2-pentanamineNH2|

CH3—CH—CH2—CH2—CH3

B. N-methyl-1-butanamine

CH3—CH2—CH2—CH2—NH—CH3

Solution

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Aromatic Amines

The amine of benzene is named aniline.

Aniline 3-Chloroaniline N-Methylaniline

NH CH3 NH2

Cl

NH2

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Boiling Points of Amines, Alcohols, and Alkanes

The boiling points of amines are higher than alkanes, but lower than alcohols of similar mass.

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Boiling points of some common amines are shown Boiling points of some common amines are shown in the Table 15.1in the Table 15.1

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Hydrogen Bonding for AminesThe polar N-H bond provides hydrogen bonding in 1°and 2° amines, but not 3°.However, the N-H bonds in amines are not as polar as the O-H bonds in alcohols.

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Solubility in WaterAmines with 1-5 carbon atoms are soluble in water.The N atom in amines forms hydrogen bonds with the polar O-H bond in water.

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Learning Check

Consider the following compounds:1) CH3—CH2—CH2—NH2

2) CH3—CH2—NH—CH3

3) CH3—CH2—CH2—CH3

A. Which compound has the highest boiling point?B. Which compound is soluble in water?

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SolutionConsider the following compounds:1) CH3—CH2—CH2—NH22) CH3—CH2—NH—CH33) CH3—CH2—CH2—CH3A. Which compound has the highest boiling point?1) CH3—CH2—CH2—NH2B. Which compound is soluble in water?1) CH3—CH2—CH2—NH22) CH3—CH2—NH—CH3

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Like ammonia, amines are weak bases in water.NH3 + H2O NH4

+ + OH–

ammonium hydroxide

CH3—NH2 + H2O CH3—NH3+ + OH–

methylammoniumhydroxide

15.4 Basicity of Amines

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An amine salt: Forms when an amine is neutralized by acid. Is named by replacing the amine part of the name with ammonium followed by the name of the negative ion.

CH3—NH2 + HCl CH3—NH3+ Cl–

Methylamine methylammonium chloride

15.5 Amine Salts

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Properties of Amine Salts Amine salts are:

Solids at room temperature.Soluble in water and body fluids.The form used for drugs.

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CocaineCocaine is sold illegally as an amine salt.Cocaine is reacted with NaOH to produce the free amine form known as “crack.”

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Heterocyclic AminesIn a heterocyclic amine, a five- or six-atom ring contains one or more nitrogen atoms.

N

NN

N

N

H

N

H

N

H

Pyrrolidine Pyrrole

Piperidine Pyridine Pyrimidine

N

N

N

N

H

Purine

N

HImidazole

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Names and structures of several heterocyclic nitrogen compounds are given in Table 15.2.

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Alkaloids are:Physiologically active nitrogen-containing compounds.Produced by plants.Used as stimulants, anesthetics, and antidepressants.Often habit forming.

Alkaloids

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Caffeine:Is a stimulant of the central nervous system. Is found in coffee beans, tea, chocolate, and soft drinks.Contains an imidazolering.

Caffeine

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NicotineNicotine:

Increases the adrenaline level in the blood.Causes addiction to tobacco.Contains a pyrrolidine ring.

N

CH3

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Alkaloids Related to MorphineAlkaloids such as morphine and codeine are produced by the poppy.For centuries, morphine and codeine have been used as painkillers.Heroin is a modification of morphine.

Methadone

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PharmacologyAn area of research in pharmacology is to design drugs with some of the characteristics of alkaloids. The structures of cocaine and morphine are modified to produce anesthesia, but without the addictive side effects.

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PharmacologyParts of the morphine structure that produce anesthesia are found in procaine, lidocaine, and demerol.

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Learning CheckIdentify the heterocyclic

amine in serotonin.

serotonin

N

HOCH2

H

CH2 NH2

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SolutionIdentify the heterocyclic amine in serotonin.

IndoleN

HOCH2

H

CH2 NH2