Chapter 14 Amines

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Chapter 14Amines
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15.1 Amines

• Amines are compounds that contain one or more
  organic groups bonded to nitrogen. They are
  classified as primary, secondary, and tertiary
  according to how many organic groups are bonded
  to the nitrogen atom.

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• The nitrogen atom in an amine has one lone
  electron pair.

• This electron pair can be shared with another
  atom forming a dative covalent bond (so called
  because the electrons are coming from one atom
  only).

• Note that the N atom acquires a positive charge
  in the process. Such N atoms are called
  quaternary ammonium ion.

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• Primary alkyl amines (RNH2) are named simply by
  identifying the alkyl group attached to the
  nitrogen and adding the suffix amine to the
  alkyl group name.

Methylamine Isopropylamine
Cyclobutylamine
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• Secondary (R2NH), and tertiary (R3N) amines with
  two or three identical groups are named by adding
  the appropriate prefix, di- or tri-, to the alkyl
  group name. For example, (CH3CH2)2NH is diethyl
  amine.

diethylamine trimethylamine
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• When the R groups are different in secondary or
  tertiary amines, the compounds are named as
  N-substituted derivatives of a primary amine

• Choose the largest group

• Create the base name from the primary amine with
  this substituent
• ethylamine

• Name the other substituent in the prefix part.
  Each substituent has the form N-Subs
  N-methylethylamine
• If there are two different substituents follow
  the naming N-Subst1-N-Subst2BaseName

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• In tertiary amines it may happen that two of the
  groups are equal. In this case use the prefix di.

Largest Group
Base name isopropylamine
Name N,N-diethylisopropylamine
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• The simplest aromatic amine is known by the
  common name aniline

• Derivatives of aniline preserve the common name

N-methylaniline
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• You can summarize the process as follows
• Choose largest group (there may be only one or
  several that are the same) and write the base
  name GroupAmine. (Use di or tri if needed)
• Are there any groups left?
• No Then you are done
• Yes Two possible cases
• One group left the name is thenN-GroupLeftBaseN
  ame.
• Two groups left Are they the same?
• B.1) Yes Name is N,N-diGroupsLeftBaseName
• B.2) No Name is N-Group1-N-Group2BaseName (in
  alphabetical order!)

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Ethylamine
N-methylethylamine
Diethylamine
N,N-dimethylpropylamine
N-ethyl-N-methylpropylamine
N-ethyl-N-methylaniline
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15.2 Properties of Amines

• The lone electron pair in amines causes them to
  be weak bases

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• Can you explain the following observations
  reagarding the boiling point of amines?

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• Primary and secondary amines are able to form
  hydrogen bonds between their molecules.

• As a result of H-bonding, primary and secondary
  amines have higher boiling points that alkanes of
  similar size.
• However, note that because N is less
  electronegative than O the H-bonds are less
  strong than in alcohols. Thus, amines B.P. are
  lower than those of alcohols.

Hydrogen bonds in diethylamine
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• Tertiary amines cannot H-bond to other molecules
  of the same type. Thus, they have lower boiling
  points than other amines of similar molecular
  weight

Trimethylamine B.P. 3 oC
Propylamine B.P. 48 oC
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• However, all amines can form H-bond with water.
  Therefore, small amines (to about 6 carbons) are
  soluble in water.
• Many amines have strong odors. They are
  responsible for the bad smell in rotten meat or
  fish.
• Many amines are physiologically active and are
  the active ingredients in drugs, irritants and
  poisons.

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15.4 Basicity of Amines

• Aqueous solutions of amines are weakly basic
  (pHgt7) because of the formation of OH- ion when
  reacting with water
• In acidic solutions the H3O ion generated from
  the dissociation of the acid can react with
  amines

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• The positive ion generated in these reactions is
  called an ammonium ion. They are named by
  replacing the amine ending by ammonium

Ethylammonium ion
trimethylammonium ion

• In the aqueous environment of blood and other
  body fluids amines are present in the form of
  ammonium ions.

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• In general, nonaromatic amines (e.g.
  methylamine) are slightly stronger bases than
  ammonia (NH3), and aromatic amines such as
  aniline are weaker bases than ammonia
• Nonaromatic amines gt Ammonia gt Aromatic Amines

Decreasing Basicity
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15.5 Amine Salts

• An ammonium salt (the salt of an amine) the
  compound formed by an ammonium cation and an
  anion.
• They are named by combining the ion names in the
  order cation and then anion
• CH3NH3Cl- CH3CH2NHCH2CH3Br-
• methylammonium chloride
  diethylammonium bromide
• Ammonium Salts are ionic compounds.

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• They are normally odorless, white, crystalline
  solids that are much more soluble in water than
  neutral amines because they are ionic.
• Many amines of pharmacological or biological
  interest are insoluble in water. In these cases,
  amines are converted into their ammonium salts
  that are easily water-soluble.

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• For pharmaceutical purposes, amines are mostly
  converted into their ammonium chloride or bromide
  salts. This is easily accomplished in the lab by
  simply combining the amine with either HCl or HBr
  and evaporating the solvent

Tributylammonium chloride (water-soluble)
Tributylamine (water-insoluble)
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• Ammonium Salts are frequently found in many
  medicines

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Scan from the back label of Nyquil
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Pseudoephedrine A nasal decongestant Not soluble
in water
Dextromethorpan A cough supressant Not soluble in
water

• Both substances are converted into salts to make
  them water-soluble. Can you write the structure
  of the salts?

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• Ammonium salts are easily converted to the free
  amine by treatment with a base

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• Quaternary Ammonium salts have four organic
  groups joined to the N atom
• Because there is no H attached to the nitrogen
  and no lone pair either. Quaternary ammonium
  salts are not bases and their structures are not
  affected by changes in pH. Many quaternary
  ammonium salts are used as detergents,
  antiseptics and disinfectants.

R -C8H17 to C18H37
Benzalkonium Chloride An antiseptic and
disinfectant-
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15.3 Heterocyclic Nitrogen Compounds

• Heterocycle A cyclic compound that contains an
  atom different from C within the ring

1,4-Dioxane (A solvent)
Pyridine (Aromatic Amine)
Piperidine (A cyclic Amine)
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15.6 Alkaloids

• Alkaloids A naturally occurring
  nitrogen-containing compound isolated from a
  plant. Most alkaloids are basic, taste bitter,
  and have physiological effects.

Caffeine
Nicotine