Chapter 15: Amines

Amine

classified as 1, 2, 3 depending on the number of carbon groups bonded to nitrogen

Aliphatic amine

all carbons bonded to nitrogen are derived from alkyl groups

Aromatic amine

one or more of the groups bonded to nitrogen are aryl groups

Heterocyclic amine

an amine in which the nitrogen atom is part of a ring

Heterocyclic aliphatic amine

a heterocyclic amine in which the ring is saturated (has no c=c bonds)

Heterocyclic aromatic amine

amine nitrogen is part of an aromatic ring

Aliphatic amine IUPAC naming

• drop the final -e of the parent alkane and replace it by -amine

• use a number to locate the amino group on the parent chain

Aniline (aromatic amine) IUPAC naming

• retain the common name aniline for C6H5NH2 (the simplest aromatic aniline

• name simple derivatives of aniline by using numbers to locate substituents of use the prefixes ortho, meta, para

C6H5NH2

simplest aromatic amine

Toluidine

one of the several derivatives of aniline widely uses common names

Unsymmetrical secondary and tertiary amine IUPAC naming

• name unsymmetrical secondary and tertiary amines as N-substituted primary amines

• take the largest group bonded to nitrogen as the parent amine

• name the smaller groups bonded to nitrogen and show their location by using the prefix N-(indicating that they are bonded to nitrogen)

Common names

for most aliphatic amines, list the groups bonded to nitrogen in alphabetical order in one word ending in the suffix -amine

Amine salt

• when 4 atoms or groups of atoms are bonded to a nitrogen atom, as for examples CH3NH3+ nitrogen bears a positive charge and is associated with anion as a salt

• nomenclature: replace the ending -amine (or aniline or pyridine) by -ammonium (or anilinium or pyridinium) and add the name of the anion

Low-molecular-weight amines

• like ammonia, have vey sharp penetrating odors

• ex: trimethylamine - pungent principle in the smell of rotting fish

• other pungent amines: 1,4-butanediamine (putrescine) and 1,5-pentanediamine (cadaverine)

Trimethylamine

pungent principle in the smell of rotting fish

1,4-butanediamine (putrescine)

rotting fish, decaying meat smell

1,5-pentanamine (cadaverine)

decaying corpses smell

Amines

are polar compounds

1° and 2° amines

• have N-H bonds

• can form hydrogen bonds with one another

3° amines

• have no N-H bond

• cannot form hydrogen bonds with one another

N-H- - -H hydrogen bond

weaker than O-H- - -O hydrogen bond because the difference in electronegativity between N and H (3.0 -2.1=0.9) is less than that between O and H (3.5-2.1=1.4)

All classes of amines

• form hydrogen bonds with water

• more soluble in water than are hydrocarbons of comparable molecular weight

Most lo-molecular-weight amines

completely soluble in water

Higher-molecular-weight amines

only moderately soluble in water or insoluble

Amines

like ammonia, they are weak bases and its aqueous solutions are basic

Acid-base reaction between an amine and water

involves transfer of a proton from water to the amine

Aliphatic amines

• have about the same base strength and are slightly stronger bases than NH3

• weak bases by comparison with inorganic bases such as NaOH, they are strong bases among organic compounds

Aromatic and heterocyclic aromatic amines

considerable weaker bases than aliphatic amines

Ammonia (NH3)

weaker base against aliphatic amines but stronger than aromatic

Basicity of amines

with it, we can determine which form of an amine exists in body fluids

7.40

in a normal, healthy person, the pH of blood is approximately _____ which is slightly basic

Aliphatic amine

if dissolved in blood, it is present predominantly as its protonated (conjugated acid) form

Conjugate acid of dopamine

major form present in blood plasma

Basicity

the most important chemical property of amines

Amines

whether soluble or insoluble in water, react quantitatively with string acids to form water-soluble salts

(R)-norepinephrine

only slightly soluble in water

(R)-norepinephrine hydrochloride

a water soluble salt