Amines Bettelheim, Brown, Campbell and Farrell Chapter 16

Amines –Amines contain a nitrogen atom that is bonded to at least one carbon group –Can think of amines as derivatives of ammonia, NH 3 –aliphatic amine: –aliphatic amine: all carbons bonded to nitrogen are derived from alkyl groups –aromatic amine: –aromatic amine: one or more of the groups bonded to nitrogen are aryl groups

Classification of Amines –Amines are classified as 1°, 2°, or 3° depending on the number of carbon groups attached to nitrogen –Aliphatic amine: –Aliphatic amine: Only alkyl groups bonded to the nitrogen –Aromatic amine: –Aromatic amine: One or more aromatic (or aryl) groups bonded to the nitrogen

Heterocyclic Amines –Heterocyclic amine: –Heterocyclic amine: Amine in which the nitrogen atom is part of a ring –Heterocyclic aliphatic amine: –Heterocyclic aliphatic amine: Heterocyclic amine in which the ring is saturated (has no C=C bonds) –Heterocyclic aromatic amine: –Heterocyclic aromatic amine: Amine nitrogen is part of an aromatic ring Important in nature

Common Names (easier) amineAliphatic amines: List the groups bonded to nitrogen in alphabetical order followed by the suffix –amine Entire name given in one word

IUPAC Nomenclature IUPAC names –IUPAC names for aliphatic amines derived in similar way as alcohol names -amine –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

IUPAC Nomenclature –Uses common name aniline for C 6 H 5 NH 2, the simplest aromatic amine –Use numbers to locate substituents OR –Use the prefixes ortho (o), meta (m), and para (p) –Several aniline derivatives have common names that are still widely used

IUPAC Nomenclature –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 group(s) bonded to nitrogen –Show their location on nitrogen by using the prefix N (indicating that they are bonded to nitrogen)

Ammonium salts N is group 5 5 valence electrons NH 3 has an unshared pair that can form a fourth bond but with a + charge on N

Nomenclature of Amine Salts Amine salts –Have four atoms or groups of atoms bonded to a nitrogen atom i.e., CH 3 NH 3 + –Nitrogen bears a positive charge –Ion is a quaternary ion-4 bonds to N with + charge –Positive ion is associated with an anion as a salt –Compound named as a salt of the corresponding amine -amine -ammoniumReplace the ending -amine (or aniline or pyridine etc.) by -ammonium (or anilinium or pyridinium etc.) Add the name of the anion

Physical Properties Small amines have very nasty, sharp, penetrating odors –Trimethylamine smells like rotting fish –Names sometimes reflect their odors: 1,4-butanediamine is putrescine 1,5-pentanediamine is cadaverine

Physical Properties Amines are polar compounds –1° and 2° amines have N-H bonds and can form hydrogen bonds with one another –3° amines have no N-H bond and cannot form hydrogen bonds with one another

Physical Properties –Hydrogen bonds between amines are weaker than hydrogen bonds between alcohols, because O is more electronegative than N –Boiling points of amines lower than those of comparable alcohols –Boiling points of amines higher than those of comparable alkanes –Compare ethane, methanamine and methanol:

Physical Properties –Amines form hydrogen bonds with water and are more soluble in water than are hydrocarbons of comparable molecular weight –Most small amines are completely soluble in water –Larger amines are only moderately soluble in water or are insoluble

Basicity of Amines Amines are weak bases Aqueous solutions of amines are basic –Acid-base reaction between an amine and water involves transfer of a proton from water to the amine BaseConjugate acid

Reactions of Amines Basicity is most important chemical property of amines –Amines, whether soluble or insoluble in water, react quantitatively with strong acids to form water-soluble salts

Basicity of Amines Aliphatic amines –Weak base –Basicity similar to ammonia –Stronger than aromatic amines Aromatic or Heterocyclic aromatic amines –Very weak base –Weaker than aliphatic amines

Basicity of Amines Which form of an amine exists in blood? –pH of blood is approximately 7.40, which is slightly basic –Thus an aliphatic amine dissolved in blood exists predominantly in its protonated (conjugate acid) form

Physical Properties of Quaternary Ammonium Salts Unlike 1 o, 2 o and 3 o amines, quaternary nitrogens have 4 bonds and a +1 charge They are associated with an anion Melting and Boiling points much higher than amines (held together by charges) Salts are much more soluble in water –Many drugs are made as hydrochloride salts rather than just free amines –Cocaine exists as “free base” or “crack” (smoked) and as HCl salt (injected)

Reactions of Amines –example: –example: complete each acid-base reaction and name the salt formed

Reactions of Amines –example: –example: complete each acid-base reaction and name the salt formed –solution:

Aminoalcohols found in Lipids Ethanolamine Choline Sphinogosine

Alkaloids Alkaloids are basic compounds obtained from plants Alkaloids contain nitrogen Alkaloids frequently have physiological effects Alkaloids are often poisonous Common names often end in “ine”

Alkaloids Cocaine Coniine (from hemlock) Caffeine

Properties of Cocaine PropertyFree Base freebase/crack HCl Salt Melting point o C98195 Solubility in H 2 O Lowhigh Solubility in fats/oils Highnone VolatilityHigh Smoked Low Injected/inhaled

Related Alkaloids Many compounds are related –Heroin: H’s replaced by acetate –Codeine: Blue H replaced by methyl Codeine Heroin Demerol Methadone

Common Drugs Amphetamine Methamphetamine