Transcript 15.2 Properties of Amines

Outline
15.1 Amines
15.2 Properties of Amines
15.3 Heterocyclic Nitrogen Compounds
15.4 Basicity of Amines
15.5 Amine Salts
15.6 Amines in Plants: Alkaloids
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Goals
1. What are the different types of amines?
Be able to recognize primary, secondary, tertiary, and
heterocyclic amines, as well as quaternary ammonium ions.
2. How are amines named?
Be able to name simple amines and write their structures,
given the names.
3. What are the general properties of amines?
Be able to describe amine properties such as hydrogen
bonding, solubility, boiling point, and basicity.
4. How do amines react with water and acids? Be able to
predict the products of the acid–base reactions of amines and
ammonium ions.
5. What are alkaloids?
Be able to describe the sources of alkaloids, name some
examples, and tell how their properties are typical of amines.
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15.1 Amines
• Amines contain one or more organic
groups bonded to nitrogen.
• Amines are organic derivatives of
ammonia (NH3).
• They are classified as primary (1°),
secondary (2°), or tertiary (3°),
according to how many organic groups are
individually bound directly to the nitrogen
atom.
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15.1 Amines
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15.1 Amines
• Each amine nitrogen atom has a lone pair
of electrons.
• The lone pair is responsible in large part
for the chemistry of amines.
• When a fourth group bonds to the nitrogen
through this lone pair, the product is a
quaternary ammonium ion, which has a
permanent positive charge and forms ionic
compounds.
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15.1 Amines
• Each amine nitrogen atom has a lone pair of
electrons.
• The lone pair is responsible in large part for the
chemistry of amines.
• When a fourth group bonds
to the nitrogen through this
lone pair, the product is a
quaternary ammonium ion,
which has a permanent
positive charge and forms
ionic compounds.
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15.1 Amines
• Primary alkyl amines (RNH2) are named by
identifying the alkyl group attached to nitrogen and
adding the suffix -amine to the alkyl group name.
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15.1 Amines
• Simple, non-heterocyclic secondary and tertiary
amines are named by adding di- or tri- to the
alkyl group name along with the suffix -amine.
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15.1 Amines
• When the R groups in secondary or tertiary
amines are different, the compounds are named
as N-substituted derivatives of a primary amine.
The parent compound is the one that contains
the largest of the R groups; all other groups are
considered to be N-substituents.
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15.1 Amines
• The —NH2 functional group is an amino group.
• When this group is a substituent, amino- is used
as a prefix in the name of the compound.
• Aromatic amines are primarily known by their
common names. The simplest aromatic amine is
known as aniline.
• Proteins are polymers of amino acids; these
have the general structure. H2N—CHR—COOH.
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15.1 Amines
Knowing What You Work With: Material Safety Data Sheets
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There are millions of different chemical compounds. If a compound is spilled, inhaled, or
ingested; what kind of clean up or first aid is required? All of the information is readily
available through what are known as Material Safety Data Sheets (MSDSs).
These documents contain basic information needed to insure the safety and health of the
user of a given chemical. MSDSs are not meant for consumers, but for occupational use;
this is primarily to limit confusion arising from the MSDSs themselves.
What does a typical MSDS contain?
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Composition and Information on ingredients;
Hazards Identification;
First Aid Measures;
Fire Fighting Measures;
Release Measures: how to deal with spills and leaks;
Handling and Storage: what precautions need to be used when handling the material;
Exposure Controls and Personal Protection: permissible exposure limits (PEL) for the
material as well as a time weighted average (TWA) for exposure over an 8-hour work shift;
this section also lists personal protective equipment required for handling the material;
8. Physical and Chemical Properties;
9. Stability and Reactivity: conditions to avoid and incompatibilities with other materials;
10. Toxicological Information;
11. Ecological Information: effects that the material has on the environment;
12. Disposal Considerations: how to safely and legally dispose of the material.
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15.2 Properties of Amines
• The lone electron pair on the nitrogen in
amines causes amines to act as weak
Brønsted–Lowry bases or Lewis bases.
• A Lewis base is a compound containing
an unshared pair of electrons.
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15.2 Properties of Amines
• Primary and secondary amines can hydrogen bond
with one another.
• Because of hydrogen bonding, primary and
secondary amines have higher boiling points than
alkanes of similar size.
• Oxygen can form more hydrogen bonds per
molecule than nitrogen; alcohols have even higher
boiling points.
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15.2 Properties of Amines
• All amines can form hydrogen bonds with water.
• Amines with up to about 6 carbon atoms have
appreciable solubility in water.
• Oxygen can form more hydrogen bonds per
molecule than nitrogen; alcohols have even
higher boiling points than amines.
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15.2 Properties of Amines
• Many volatile amines have strong odors.
Some smell like ammonia and others like
stale fish or decaying meat.
• Simpler amines are irritating to the skin, eyes,
and mucous membranes and are toxic by
ingestion.
• Some more complex amines from plants can
be very poisonous.
• All living things contain a wide variety of
amines, and many useful drugs are amines.
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15.2 Properties of Amines
Properties of Amines
• Primary and secondary amines can hydrogen-bond with each
other and thus, are higher boiling than alkanes, but lower
boiling than alcohols.
• Tertiary amines are lower boiling than secondary or primary
amines because hydrogen bonding between tertiary amines is
not possible.
• The simplest amines are gases; other common amines are
liquids.
• Volatile amines have unpleasant odors.
• Simple amines are water-soluble because of hydrogen
bonding with water.
• Amines are weak Brønsted–Lowry/Lewis bases.
• Many amines are physiologically active, and many are toxic.
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15.3 Heterocyclic Nitrogen Compounds
• In many nitrogen-containing compounds, the
nitrogen atom is in a ring with carbon atoms.
• Compounds that contain atoms other than
carbon in the ring are known as heterocycles.
• Heterocyclic nitrogen compounds may be
nonaromatic or aromatic.
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15.3 Heterocyclic Nitrogen Compounds
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15.4 Basicity of Amines
• Aqueous solutions of amines are weakly
basic.
CH3CH2NH2 + H2O ⇆ CH3CH2NH3+ + OH–
(CH3CH2) 2NH + H2O ⇆ (CH3CH2)2NH2+ + OH–
(CH3CH2) 3N + H2O ⇆ (CH3CH2)3NH+ + OH–
• An ammonium ion is a positive ion formed
by addition of hydrogen to an amine.
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15.4 Basicity of Amines
• Alkylamine cations are named by replacing
the ending -amine with -ammonium.
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15.4 Basicity of Amines
• Heterocyclic amine cations are named by
replacing the -e with -ium.
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15.4 Basicity of Amines
• In general, nonaromatic amines are
slightly stronger bases than ammonia, and
aromatic amines are weaker bases than
ammonia.
nonaromatic amines > ammonia > aromatic amines
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15.4 Basicity of Amines
Organic Compounds in Body Fluids and the “Solubility Switch”
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Chemical reactions that keep us alive and functioning occur in bodyfluids, and waste
products from these metabolic reactions are excreted in urine.
Water solubility decreases as hydrocarbon-like portions of molecules become larger,
but many biomolecules contain acidic and basic functional groups.
At the pH of body fluids (approximately 7.2), many of these groups are ionized and
soluble. The most common functional groups are carboxylate groups, phosphate
groups, and ammonium groups.
Most biochemical pathways occur in the cytosol. Diffusion of reactants does not occur
because the intermediates are ionized; as a result, they cannot pass through the
nonpolar cell wall.
Medications must be soluble in body fluids to be transported from their entry point to
their site of action.
Weak acids are un-ionized in the acidic environment in the stomach and are therefore
readily absorbed there.
Weak bases are completely ionized in the stomach. In the basic environment of the
small intestine, weak bases revert to their neutral form and are absorbed.
Converting amines such as phenylephrine (the decongestant in Neo-Synephrine) to
ammonium hydrochlorides increases their solubility to the point where delivery in
solution is possible.
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15.5 Amine Salts
• Ammonium salt is an ionic compound
composed of an ammonium cation and an
anion; an amine salt.
• They are named by combining the ion
names; NH4Cl is ammonium chloride.
• Ammonium salts are generally odorless,
white, crystalline solids that are much more
soluble than neutral amines.
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15.5 Amine Salts
• In medicinal chemistry, amine salt
formulas are quite often written and
named by combining the structures and
names of the amine and the acid used to
form its salt.
• By this system, methylammonium chloride
is written CH3NH2•HCl and named
methylamine hydrochloride.
• If a free amine is needed, it is easily
regenerated by treatment with a base.
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15.5 Amine Salts
• Quaternary ammonium ions have four
organic groups bonded to the nitrogen
atom, giving the nitrogen a positive
charge.
• With no H atom and no lone pair,
ammonium ions are neither acidic nor
basic, and their structures in solution are
unaffected by changes in pH.
• Their salts are known as quaternary
ammonium salts.
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15.5 Amine Salts
• Benzalkonium chlorides have antimicrobial
and detergent properties. As dilute
solutions, they are used in surgical scrubs
and for sterile storage of instruments.
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15.6 Amines in Plants: Alkaloids
• Alkaloids are naturally occurring,
nitrogen-containing compounds isolated
from a plant; usually basic, bitter, and
poisonous.
• Many thousands of alkaloids have been
characterized.
• The bitterness and poisonous nature of
alkaloids probably protects plants from
being devoured by animals.
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15.6 Amines in Plants: Alkaloids
• Coniine is extracted from poison hemlock
(Conium maculatum). Socrates used this poison
to end his life after being convicted of corrupting
Greek youth with his philosophical discussions.
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15.6 Amines in Plants: Alkaloids
• Atropine is the toxic
substance in the herb known
as deadly nightshade or
belladonna (Atropa
belladonna).
• Atropine acts on the central
nervous system, a property
applied in medications to
reduce cramping of the
digestive tract.
• Atropine is also used as an
antidote against nerve gases,
such as Sarin.
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15.6 Amines in Plants: Alkaloids
• Solanine is found in potatoes and tomatoes,
both of which belong to the same botanical
family as the deadly nightshade (Solanaceae).
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15.6 Amines in Plants: Alkaloids
• When potatoes are exposed to sunlight or
stored under very cold or very warm
conditions, the production of solanine is
increased to levels that can be dangerous.
• Alkaloids are not destroyed during cooking
but can be removed by peeling.
• Sunlight also stimulates the formation of
chlorophyll under the skin of the potato,
and the green color of the chlorophyll
provides a warning.
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15.6 Amines in Plants: Alkaloids
• About 20 alkaloids are present in the poppy,
including morphine and codeine. The free
alkaloids are oily liquids.
• The medicinal use of morphine for pain was
expanded when the German physician
Paracelsus extracted opium into brandy to
produce laudanum.
• A similar extract is still sometimes prescribed,
as is paregoric, a more dilute solution of
opium combined with anise oil, glycerin,
benzoic acid, and camphor.
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15.6 Amines in Plants: Alkaloids
• Heroin does not occur naturally, but is easily
synthesized from morphine. Within the body,
removal of the CH3=O groups (highlighted in
orange) converts heroin back to morphine.
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15.6 Amines in Plants: Alkaloids
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Toxicology is the science devoted to poisons—identification, effects, modes
of action, and methods of protecting against them.
Clinical toxicology is concerned with the treatment of individuals harmed by
toxic agents.
Forensic toxicology deals with the effects of toxic agents as they relate to
criminal cases, most notably in drug abuse or intentional poisonings.
Environmental toxicology—is concerned with toxic substances purposefully
or accidentally introduced into our surroundings.
Many poisons have a molecular structure that allows them to interact with a
specific biomolecule. Several of the most poisonous substances known are
neurotoxins, which bind to proteins that form ion channels in nerve cell
membranes. Blocking these channels prevents transmission of nerve
impulses, causing paralysis and death by suffocation.
A number of poisons act at receptors that normally bind acetylcholine, a
neurotransmitter (a molecule that carries chemical messages between
nerve cells).
A thorough understanding of any poison includes knowing how it acts at the
molecular level and knowing a molecular mechanism by which its effects
can be reversed.
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Chapter Summary
Summary of Reactions
1. Reactions of amines (Section 15.4)
a. Acid–base reaction with water:
CH3CH2NH2 + H2O ⇆ CH3CH2NH3+ + OH–
b. Acid–base reaction with a strong acid to yield
an ammonium ion:
CH3CH2NH2 + HCl ⇆ CH3CH2NH3+ + Cl–
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Chapter Summary, Continued
Summary of Reactions
1. Reaction of ammonium ion (Section
15.4) or amine salt (Section 15.5)
a. Acid–base reaction of primary, secondary, or
tertiary amine salt (or ion) with a base to
regenerate the amine:
CH3CH2NH3+Cl– + NaOH ⇆ CH3CH2NH2 + NaCl +
H2O
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Chapter Summary, Continued
1. What are the different types of amines?
• Amines are classified as primary, secondary, or
tertiary, depending on whether they have one, two,
or three organic groups individually bonded to
nitrogen.
• These amines can all add hydrogen to form
ammonium ions, which have four bonds to the
nitrogen, which bears a single positive charge.
• Ions with four organic groups bonded to nitrogen
are known as quaternary ammonium ions.
• In heterocyclic amines, the nitrogen of the amine
group is bonded to 2 carbon atoms that are part of
a ring.
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Chapter Summary, Continued
2. How are amines named?
• Primary amine names have -amine added to the
alkyl group name, and secondary and tertiary
amines with identical R groups have di- and triprefixes.
• When the R groups are different, amines are
named as N-substituted derivatives of the amine
with the largest R group.
• Ions derived from amines are named by
replacing -amine in the name with -ammonium.
The NH2 group as a substituent is called an
amino group.
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Chapter Summary, Continued
3. What are the general properties of amines?
• Amines have an unshared electron pair on nitrogen
that is available to accept a proton or for hydrogen
bonding.
• Primary and secondary amine molecules hydrogenbond to each other, but tertiary amine molecules
cannot do so. Thus, the general order of boiling points
for molecules of comparable size is:
Hydrocarbons<tertiary amines< primary and secondary amines< alcohols
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All amines can, however, hydrogen-bond to other
molecules containing OH and NH groups, and for this
reason small amine molecules are water-soluble. Many
amines are physiologically active. Volatile amines have
strong, unpleasant odors.
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Chapter Summary, Continued
4. How do amines react with water and
acids?
• Amines are weak bases and establish
equilibria with water by adding H+ to form
ammonium ions (RNH3+, R2NH2+, and R3NH+)
and hydroxide ions (OH–).
• They react with acids to form ammonium
salts. Ammonium ions react as acids (proton
donors) in the presence of a base.
• Quaternary ammonium ions R4N have no
lone electron pair and are not bases, nor can
they form hydrogen bonds.
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Chapter Summary, Continued
5. What are alkaloids?
• Alkaloids are naturally occurring nitrogen
compounds found in plants.
• They are all bases, most with a bitter
taste.
• Like other amines, many are
physiologically active, notably as poisons
or analgesics.
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