chapter 7 amines and amides

Chapter 7Amines and Amides

General, Organic, and Biological Chemistry, Fifth EditionH. Stephen Stoker

Brroks/Cole Cengage Learning. Permission required for reproduction or display.

Prepared by:GIZEL R. SANTIAGO

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Chapter 7 Topics• Bonding Characteristics of Nitrogen Atoms in Organic

Compounds • Structure and Classification of Amines • Nomenclature for Amines • Isomerism for Amines • Physical Properties of Amines • Basicity of Amines • Amine Salts • Preparation of Amines and Quaternary Ammonium

Salts

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Chapter 7 Topics• Heterocyclic Amines • Selected Biochemically Important Amines • Alkaloids • Structure of and Classification of Amides • Nomenclature for Amides • Selected Amides and Their Uses • Physical Properties of Amides • Preparation of Amides • Hydrolysis of Amides • Polyamides and Polyurethanes

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Bonding Characteristics of Nitrogen Atoms in Organic Compounds

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Structure and Classifications of Amines

An amine is an organic derivative of ammonia (NH3) in which one or more alkyl, cycloalkyl, or aryl groups are attached to the nitrogen atom. Amines are classified as primary (10), secondary (20), or tertiary (30) on the basis of how many hydrocarbon groups are bonded to the ammonia nitrogen atom.

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A primary amine is an amine in which the nitrogen atom is bonded to one hydrocarbon group and two hydrogen atoms. The generalized formula for a primary amine is RNH2. A secondary amine is an amine in which the nitrogen atom is bonded to two hydrocarbon groups and one hydrogen atom. The generalized formula for a secondary amine is R2NH.

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A tertiary amine is an amine in which the nitrogen atom is bonded to three hydrocarbon groups and no hydrogen atoms. The generalized formula for a tertiary amine is R3N.

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Structure and Classifications of AminesThe basis for the amine primary-secondary-tertiary classification system differs from that for alcohols. 1.For alcohols we look at how many R groups

are on a carbon atom, the hydroxyl bearing carbon atom.

2.For amines we look at how many R groups are on the nitrogen atom.

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Tert-butyl alcohol is a tertiary alcohol, whereas tert-butylamine is a primary amine.

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The functional group present in a primary amine, the —NH2 group, is called an amino group. An amino group is the —NH2 functional group. Secondary and tertiary amines possess substituted amino groups.

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Nomenclature for AminesBoth common and IUPAC names are extensively used for amines. In the common system of nomenclature, amines are named by listing the alkyl group or groups attached to the nitrogen atom in alphabetical order and adding the suffix -amine; all of this appears as one word. Prefixes such as di- and tri- are added when identical groups are bonded to the nitrogen atom.

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Nomenclature for Amines

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Nomenclature for AminesThe IUPAC rules for naming amines are similar to those for alcohols. Alcohols are named as alkanols and amines are named as alkanamines. IUPAC rules for naming primary amines are as follows: Rule 1: Select as the parent carbon chain the longest chain to which the nitrogen atom is attached.

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Nomenclature for AminesRule 2: Name the parent chain by changing the -e ending of the corresponding alkane name to -amine. Rule 3: Number the parent chain from the end nearest the nitrogen atom. Rule 4: The position of attachment of the nitrogen atom is indicated by a number in front of the parent chain name.

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Nomenclature for AminesRule 5: The identity and location of any substituents are appended to the front of the parent chain name.

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Nomenclature for AminesIn diamines, the final -e of the carbon chain name is retained for ease of pronunciation. Thus the base name for a four-carbon chain bearing two amino groups is butanediamine.

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Secondary and tertiary amines are named as N-substituted primary amines. The largest carbon group bonded to the nitrogen is used as the parent amine name. The names of the other groups attached to the nitrogen are appended to the front of the base name, and N- or N,N- prefixes are used to indicate that these groups are attached to the nitrogen atom rather than to the base carbon chain.

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Isomerism for AminesConstitutional isomerism in amines can arise from several causes. Different carbon atom arrangements produce isomers.

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Isomerism for AminesDifferent positioning of the nitrogen atom on a carbon chain is another cause for isomerism, illustrated in the following compounds.

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Isomerism for AminesFor secondary and tertiary amines, different partitioning of carbon atoms among the carbon chains present produces constitutional isomers. There are three C4 secondary amines; carbon atom partitioning can be two ethyl groups, a propyl group and a methyl group, or an isopropyl group and a methyl group.

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Isomerism for Amines

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Physical Properties for AminesThe methylamines (mono-, di-, and tri-) and ethylamine are gases at room temperature and have ammonia-like odors. Most other amines are liquids, and many have odors resembling that of raw fish. A few amines, particularly diamines, have strong, disagreeable odors.

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Physical Properties for Amines

The foul odor arising from dead fish and decaying flesh is due to amines released by the bacterial decomposition of protein. Two of these “odoriferous” compounds are the diamines putrescine and cadaverine.

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The simpler amines are irritating to the skin, eyes, and mucous membranes and are toxic by ingestion. Aromatic amines are generally toxic. Many are readily absorbed through the skin and affect both the blood and the nervous system.

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Physical Properties for AminesThe boiling points of amines are intermediate between those of alkanes and alcohols of similar molecular mass. They are higher than alkane boiling points, because hydrogen bonding is possible between amine molecules but not between alkane molecules. Intermolecular hydrogen bonding of amines involves the hydrogen atoms and nitrogen atoms of the amino groups.

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Amines with fewer than six carbon atoms are infinitely soluble in water. This solubility results from hydrogen bonding between the amines and water. Even tertiary amines are water-soluble, because the amine nitrogen atom has a nonbonding electron pair that can form a hydrogen bond with a hydrogen atom of water.

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Basicity of Amines

Amines, like ammonia, are weak bases.

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Basicity of Amines

The result of the interaction of an amine with water is a basic solution containing substituted ammonium ions and hydroxide ions. A substituted ammonium ion is an ammonium ion in which one or more alkyl, cycloalkyl, or aryl groups have been substituted for hydrogen atoms.

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Basicity of AminesTwo important generalizations apply to substituted ammonium ions. 1. Substituted ammonium ions are charged species

rather than neutral molecules. 2. The nitrogen atom in an ammonium ion or a

substituted ammonium ion participates in four bonds. In a neutral compound, nitrogen atoms form only three bonds. Four bonds about a nitrogen atom are possible, however, when the species is a positive ion because the fourth bond is a coordinate covalent bond.

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Basicity of Amines

Naming the positive ion that results from the interaction of an amine with water is based on the following two rules: Rule 1: For alkylamines, the ending of the name of the amine is changed from amine to ammonium ion.

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Basicity of Amines

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Basicity of Amines

Rule 2: For aromatic amines, the final -e of the name of the amine is replaced by -ium ion.

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Basicity of Amines

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Basicity of Amines

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Amine SaltsThe reaction of an acid with a base (neutralization) produces a salt. Because amines are bases, their reaction with an acid produces a salt, an amine salt.

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Amine SaltsAromatic amines react with acids in a similar manner.

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Amine SaltsAn amine salt is an ionic compound in which the positive ion is a mono-, di-, or trisubstituted ammonium ion (RNH30, R2NH20, or R3NH0) and the negative ion comes from an acid. Amine salts can be obtained in crystalline form (odorless, white crystals) by evaporating the water from the acidic solutions in which amine salts are prepared.

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Amine SaltsAmine salts are named using standard nomenclature procedures for ionic compounds. The name of the positive ion, the substituted ammonium or anilinium ion, is given fi rst and is followed by a separate word for the name of the negative ion.

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Amine SaltsAn older naming system for amine salts, still used in the pharmaceutical industry, treats amine salts as amine–acid complexes rather than as ionic compounds. In this system, the amine salt made from dimethylamine and hydrochloric acid is named and represented as

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Amine SaltsThe process of forming amine salts with acids is an easily reversed process. Treating an amine salt with a strong base such as NaOH regenerates the “parent” amine.

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Amine SaltsThe “opposite nature” of the processes of amine salt formation from an amine and the regeneration of the amine from its amine salt can be diagrammed as follows:

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Amine SaltsBecause amines and their salts are so easily interconverted, the amine itself is often designated as the free amine or free base or as the deprotonated form of the amine, to distinguish it from the protonated form of the amine, which is present in the amine salt.

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Amine Salts

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Amine Salts

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Amine Salts

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Preparation of Amines and Quaternary Ammonium SaltsGeneralized equations for the alkylation process are:

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Preparation of Amines and Quaternary Ammonium SaltsAlkylation under basic conditions is actually a two-step process. In the fi rst step, using a primary amine preparation as an example, an amine salt is produced.

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Preparation of Amines and Quaternary Ammonium SaltsThe second step, which involves the base present (NaOH), converts the amine salt to free amine.

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Preparation of Amines and Quaternary Ammonium SaltsA specific example of the production of a primary amine from ammonia is the reaction of ethyl bromide with ammonia to produce ethylamine. The chemical equation (with both steps combined) is

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Preparation of Amines and Quaternary Ammonium SaltsIf the newly formed primary amine produced in an ammonia alkylation reaction is not quickly removed from the reaction mixture, the nitrogen atom of the amine may react with further alkyl halide molecules, giving, in succession, secondary and tertiary amines.

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Preparation of Amines and Quaternary Ammonium Salts

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Preparation of Amines and Quaternary Ammonium SaltsTertiary amines react with alkyl halides in the presence of a strong base to produce a quaternary ammonium salt. A quaternary ammonium salt is an ammonium salt in which all four groups attached to the nitrogen atom of the ammonium ion are hydrocarbon groups.

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Preparation of Amines and Quaternary Ammonium SaltsCompounds that contain quaternary ammonium ions are important in biochemical systems. Choline and acetylcholine are two important quaternary ammonium ions present in the human body. Choline has important roles in both fat transport and growth regulation. Acetylcholine is involved in the transmission of nerve impulses.

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Heterocyclic AminesA heterocyclic amine is an organic compound in which nitrogen atoms of amine groups are part of either an aromatic or a nonaromatic ring system. Heterocyclic amines are the most common type of heterocyclic organic compound.

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Heterocyclic AminesHeterocyclic amine structures shows that (1) ring systems may be saturated, unsaturated, or aromatic, (2) more than one nitrogen atom may be present in a given ring, and (3) fused ring systems often occur.

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Heterocyclic Amines

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Heterocyclic Amines

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Heterocyclic Amines

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Selected Biochemically Important AminesNeurotransmitters A neurotransmitter is a chemical substance that is released at the end of a nerve, travels across the synaptic gap between the nerve and another nerve, and then bonds to a receptor site on the other nerve, triggering a nerve impulse.

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Selected Biochemically Important AminesNeurotransmitters The most important neurotransmitters in the human body are acetylcholine and the amines norepinephrine, dopamine, and serotonin.

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Selected Biochemically Important Amines

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Selected Biochemically Important AminesEpinephrineEpinephrine, also known as adrenaline, has some neurotransmitter functions but is more important as a central nervous system stimulant.

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Selected Biochemically Important AminesHistamine The heterocyclic amine histamine is responsible for the unpleasant effects felt by individuals susceptible to hay fever and various pollen allergies.

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AlkaloidsAn alkaloid is a nitrogen-containing organic compound extracted from plant material.

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AlkaloidsThese three compounds have similar chemical structures.

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Alkaloids

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Structure and Classification of AmidesAn amide is a carboxylic acid derivative in which the carboxyl —OH group has been replaced with an amino or a substituted amino group.

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Structure and Classification of AmidesAmides, like amines, can be classified as primary (10), secondary (20), or tertiary (30), depending on how many hydrogen atoms are attached to the nitrogen atom.

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Structure and Classification of AmidesA primary amide is an amide in which two hydrogen atoms are bonded to the amide nitrogen atom. Such amides are also called unsubstituted amides. A secondary amide is an amide in which an alkyl (or aryl) group and a hydrogen atom are bonded to the amide nitrogen atom. Monosubstituted amide is another name for this type of amide.

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Structure and Classification of AmidesA tertiary amide is an amide in which two alkyl (or aryl) groups and no hydrogen atoms are bonded to the amide nitrogen atom. Such amides are disubstituted amides.

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Structure and Classification of Amides

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Structure and Classification of AmidesThe simplest amide has a hydrogen atom attached to an unsubstituted amide functional group.

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Structure and Classification of AmidesNext in complexity are amides in which a methyl group is present. There are two of them, one with the methyl group attached to the carbon atom and the other with the methyl group attached to the nitrogen atom.

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Structure and Classification of AmidesThe first of these structures is a 10 amide, and the second structure is a 20 amide. The structure of the simplest aromatic amide involves a benzene ring to which an unsubstituted amide functional group is attached.

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Structure and Classification of AmidesCyclic amide structures are possible. Examples of such structures include

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Structure and Classification of AmidesCyclic amides are called lactams, a term that parallels the use of the term lactones for cyclic esters

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Structure and Classification of AmidesA lactam is a cyclic amide. The ring size in a lactam is indicated using a Greek letter. A lactam with a four-membered ring is a b-lactam because the b carbon from the carbonyl group is bonded to the heteroatom. A lactam with a five-membered ring is a g-lactam.

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Structure and Classification of AmidesThe members of the penicillin family of antibiotics have structures that contain a b-lactam ring.

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Nomenclature for AmidesRule 1: T he ending of the name of the carboxylic acid is changed from -ic acid (common) or -oic acid (IUPAC) to -amide. For example, benzoic acid becomes benzamide. Rule 2: T he names of groups attached to the nitrogen (20 and 30 amides) are appended to the front of the base name, using an N- prefi x as a locator.

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Nomenclature for Amides

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Nomenclature for AmidesNomenclature for secondary and tertiary amides, amides with substituted amino groups, involves use of the prefix N-, a practice we previously encountered with amine nomenclature

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Nomenclature for AmidesThe simplest aromatic amide, a benzene ring bearing an unsubstituted amide group, is called benzamide. Other aromatic amides are named as benzamide derivatives.

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Selected Amides and their UsesThe simplest naturally occurring amide is urea, a water-soluble white solid produced in the human body from carbon dioxide and ammonia through a complex series of metabolic reactions.

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Selected Amides and their Uses

Urea is a one-carbon diamide. Its molecular structure is

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Melatonin is a polyfunctional amide; amine and ether groups are also present.

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Barbiturates, which are cyclic amide compounds, are a heavily used group of prescription drugs that cause relaxation (tranquilizers), sleep (sedatives), and death (overdoses). All barbiturates are derivatives of barbituric acid, a cyclic amide that was first synthesized from urea and malonic acid.

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Physical Properties of AmidesAmides do not exhibit basic properties in solution as amines do. Methanamide and its N-methyl and N,N-dimethyl derivatives (the simplest 10, 20, and 30 amides, respectively), are all liquids at room temperature. All unbranched primary amides, except methanamide, are solids at room temperature, as are most other amides.

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Physical Properties of AmidesIn many cases, the amide melting point is even higher than that of the corresponding carboxylic acid. Amides of low molecular mass, up to five or six carbon atoms, are soluble in water.

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Preparation of Amides

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Preparation of AmidesAn amidification reaction is the reaction of a carboxylic acid with an amine (or ammonia) to produce an amide. In amidification, an —OH group is lost from the carboxylic acid, a —H atom is lost from the ammonia or amine, and water is formed as a by-product. Amidification reactions are thus condensation reactions.

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Hydrolysis of AmidesIn amide hydrolysis, the bond between the carbonyl carbon atom and the nitrogen is broken, and free acid and free amine are produced. Amide hydrolysis is catalyzed by acids, bases, or certain enzymes; sustained heating is also often required.

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Hydrolysis of Amides

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Hydrolysis of AmidesAcidic or basic hydrolysis conditions have an effect on the products. Acidic conditions convert the product amine to an amine salt. Basic conditions convert the product carboxylic acid to a carboxylic acid salt.

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Polyamides and Polyurethanes

Amide polymers—polyamides—are synthesized by combining diamines and dicarboxylic acids in a condensation polymerization reaction. A polyamide is a condensation polymer in which the monomers are joined through amide linkages.

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Polyamides and PolyurethanesThe most important synthetic polyamide is nylon. Nylon is used in clothing and hosiery, as well as in carpets, tire cord, rope, and parachutes. It also has nonfiber uses; for example, it is used in paint brushes, electrical parts, valves, and fasteners. It is a tough, strong, nontoxic, nonflammable material that is resistant to chemicals. Surgical suture is made of nylon because it is such a strong fiber.

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Polyamides and PolyurethanesA urethane is a hydrocarbon derivative that contains a carbonyl group bonded to both an —OR group and a —NHR (or –NR2) group. Such compounds are prepared by reaction of an alcohol with an isocyanate (R-N=C-O).

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A polyurethane is a polymer formed from the reaction of dialcohol and diisocyanate monomers. The monomers benzene diisocyanate and ethylene glycol are the reactants.

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End of Chapter 7Amines and Amides

General, Organic, and Biological Chemistry, Fifth EditionH. Stephen Stoker

Brroks/Cole Cengage Learning. Permission required for reproduction or display.

Prepared by:GIZEL R. SANTIAGO

chapter 7 amines and amides

Science