10-1 Chemistry 2060, Spring 2060, LSU Chapter 10: Amines Sections

10-2 Chemistry 2060, Spring 2060, LSU Sections Chapter 10: Amines 1.Introduction 2.Structure and classification 3.Nomenclature 4.Physical Properties 5.Basicity of amines 6.Reaction with acids 7.Synthesis of arylamines: Reduction of –NO2 group 8.Reactions of primary amines with nitrous acid

10-3 Chemistry 2060, Spring 2060, LSU Structure & Classification Classification 1°, 2°, or, 3° amines1°, 2°, or, 3° amines: amines in which 1, 2, or 3 hydrogens of NH 3 are replaced by alkyl or aryl groups 4° amines4° amines: ions in which nitrogen is bonded to four carbons and bears a positive charge

10-4 Chemistry 2060, Spring 2060, LSU Structure & Classification Amines are further divided into aliphatic, aromatic, and heterocyclic amines aliphatic aminealiphatic amine: an amine in which nitrogen is bonded only to alkyl groups aromatic aminearomatic amine: an amine in which nitrogen is bonded to one or more aryl groups

10-5 Chemistry 2060, Spring 2060, LSU Structure & Classification heterocyclic amineheterocyclic amine: an amine in which nitrogen is one of the atoms of a ring

10-6 Chemistry 2060, Spring 2060, LSU Structure & Classification Example: classify each amino group by type

10-7 Chemistry 2060, Spring 2060, LSU Nomenclature Aliphatic amines: replace the suffix -e of the parent alkane by -amine The IUPAC system retains the common name aniline

10-8 Chemistry 2060, Spring 2060, LSU Nomenclature Among the various functional groups discussed in the text, -NH 2 has one of the lowest priorities

10-9 Chemistry 2060, Spring 2060, LSU Nomenclature Common names for most aliphatic amines are derived by listing the alkyl groups bonded to nitrogen in one word ending with the suffix - amine

10-10 Chemistry 2060, Spring 2060, LSU Physical Properties Amines are polar compounds, and both 1° and 2° amines form intermolecular hydrogen bonds N-H N hydrogen bonds are weaker than O-H O hydrogen bonds because the difference in electronegativity between N and H ( = 0.9) is less than that between O and H ( = 1.4)

10-11 Chemistry 2060, Spring 2060, LSU Basicity All amines are weak bases, and aqueous solutions of amines are basic

10-12 Chemistry 2060, Spring 2060, LSU Basicity it is also common to discuss the basicity of amines by reference to the acid ionization constant of the corresponding conjugate acid for any acid-conjugate base pair

10-13 Chemistry 2060, Spring 2060, LSU Basicity Using values of pK a, we can predict the position of equilibrium in acid-base reactions acetic acid is the stronger acid and, therefore, the position of this equilibrium lies to the right

10-14 Chemistry 2060, Spring 2060, LSU Basicity aliphatic amines have about the same base strength, pK b , and are slightly stronger bases than ammonia

10-15 Chemistry 2060, Spring 2060, LSU Basicity aromatic amines are considerably weaker bases than aliphatic amines

10-16 Chemistry 2060, Spring 2060, LSU Basicity aromatic amines are weaker bases than aliphatic amines because the resonance stabilization of the free base is lost on protonation

10-17 Chemistry 2060, Spring 2060, LSU Basicity Electron-withdrawing groups, such as halogen, nitro, and carbonyl, decrease the basicity of aromatic amines by decreasing the availability of the electron pair on nitrogen

10-18 Chemistry 2060, Spring 2060, LSU Basicity Example: select the stronger base in each pair of amines

10-19 Chemistry 2060, Spring 2060, LSU Guanidine Guanidine, pK b 0.4, is the strongest base among neutral organic compounds its basicity is due to the delocalization of the positive charge over the three nitrogen atoms

10-20 Chemistry 2060, Spring 2060, LSU Reaction with Acids All amines, whether soluble or insoluble in water, react quantitatively with strong acids to form water-soluble salts

10-21 Chemistry 2060, Spring 2060, LSU Synthesis of 1° Arylamines Most are synthesized by nitration of an aromatic ring followed by catalytic reduction of the nitro group to a primary amine

10-22 Chemistry 2060, Spring 2060, LSU Reaction with Nitrous Acid Nitrous acid is a weak acid, most commonly prepared by treating an aqueous solution of NaNO 2 with H 2 SO 4 or HCl nitrous acid reacts with amines of different types, depending on whether the amine is 1°, 2°, 3° and whether it is aliphatic or aromatic we concentrate on the reaction of nitrous acid with 1° aromatic amines because this reaction is useful in organic synthesis

10-23 Chemistry 2060, Spring 2060, LSU Reaction with Nitrous Acid Treating a 1° aromatic amine with HNO 2 gives a diazonium salt warming the aqueous solution of the diazonium salt gives a phenol and N 2 gas

10-24 Chemistry 2060, Spring 2060, LSU Reaction with Nitrous Acid Example: show how to bring about each step in this conversion