10D. Amines

Question 1

Amines

Answer 1

• organic compounds derived from ammonia in which one or more hydrogen atoms is replaced with organic groups
• the functional group of an amine is an amino group - a nitrogen bonded to one, two or three carbon atoms

C - N

• amines are classified as primary (1^o), secondary (2^o) or tertiary (3^o), depending on the number of carbon groups attached to the nitrogen
• primary amines have one carbon group attached to the nitrogen atom
• secondary amines have two carbon groups attached to the nitrogen atom
• tertiary amines have three carbon groups attached to the nitrogen atom
• amines are further classified as aliphatic or aromatic
• for alyphatic amines, the nitrogen is bonded only to alkyl groups or hydrogen atoms
• for aromatic amines, the nitrogen is bonded to one or more aromatic rings
• an amine in which the nitrogen atom is part of a ring is a heterocyclic amine. When the ring is saturated, it is classified as a heterocyclic aliphatic amine. When the ring is aromatic, it is classified as a heterocyclic aromatic amine
• structurally, an amine has a similar shape to ammonia, with four regions of alectron density about the nitrogen atom, making it tetrahedral. The bond angles are 108.7^o because nitrogen has one unshared pair of electrons. These electrons form one corner of the tetrahedron, + are therefore out in space . This is important as this unshared electron pair is involved in almost all reactions of amines

Question 2

Naming

Answer 2

• similar to alcohols, except that the parent chain contains the amino group+ the final -e of the parent alkane is replaced by -amine + the location of the amino group is shown
• the simplest aromatic amine retains the common name of aniline. Its simple derivatives use numbers or the locators ortho (o), meta )m) or para (p) to locate substituents
• unsymmetrical secondary + tertiary amines are commonly named as N-substituted primary amines. The largest group bonded to nitrogen is the parent amine + the smaller groups bonded to nitrogen are named with their locations indicated by 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
• when four atoms or groups of aoms are bonded to a nitrogen atom, nitrogen has a positive charge + is associated with an ion as a salt. The compound is named as a salt of the corresponding amine. The ending -amine is replaced with -ammonium, followed by the name of the anion

Question 3

Physical Properties

Answer 3

• like ammonia, low molecular weight amines have very sharp, penetrating odours
• amines are polar compounds because of the difference in electronegativity between nitrogen + hydrogen, producing a partial negative charge on the nitrogen atom + a partial positive charge on each of the attached hydrogen atoms
• primary + secondary amines form strong hydrogen bonds with each other + with water
• tertiary amines do not form hydrogen bonds with each other because there is no hydrogen bonded to the nitrogen, but they can form hydrogen bonds with water
• amines have higher boiling points than alkanes but lower than alcohols of comparable molecular weigh
• tertiary amines generally boil at lower temperatures than primary + secondary amines of comparable molecular weight as a result of the difference in hydrogen bonding
• all amines are more solyble in water that hydrocarbons of comparable molecular weight
• most low molecular weight amines are completely soluble in water, but higher molecular weight amines are only moderately soluble in water or insoluble

Question 4

Reactions

Answer 4

• most important chemical property of amines is their basicity
• amines react with strong acids to form water-soluble salts
• the basicity of amines + solubility of amine salts in water provides a way to separate water-insoluble amines from water-insoluble non basic compounds
• all aliphatic amines have approximately the same base strength + are slightly stronger bases than ammonia
• aromatic amines + heterocyclic aromatic amines are considerably weaker bases that aliphatic amines
• while aliphatic amines are weak bases by comparison with inorganic bases, they are strong bases among organic compounds
• for the acid-base reaction between an amine + water, the unshared pair of electrons on nitrogen forms a new covalent bond with hydrogen + displaces a hydroxide ion