C28 amines

• amines are derivatives of ammonia, where one or more of the hydrogen atoms have been replaced by an alkyl group or by an aryl group
• amines can be primary, secondary or tertiary, depending on number of R groups and hydrogens
• primary amines have the form NH2R
• secondary amines have the form NHRR'
• tertiary amines have the form NRR'R''
• rules for naming amines:

  • use the suffix -amine
  • use the prefix representing number of carbon atoms in the chain
  • if it contains a ring, use the prefix -phenyl
  • if it has multiple different substituents, use the form N-alkylalkylamine with alkyl groups in alphabetical order
• amines are polar because hydrogen is delta-positive and nitrogen is delta-negative, so they can form hydrogen bonds with each other
• the hydrogen bonds between amines are not as strong as those in alcohols because nitrogen is not as electronegative as oxygen
• amines with chains up to 4 carbons long are very soluble in water and alcohols because they form hydrogen bonds, but amines with benzene rings cannot form hydrogen bonds because the ring is too large and non-polar
• amines have a lone pair of electrons which they can use to:

  • act as a base and form a bond with a H+ ion
  • act as a nucleophile and form a bond with an electron-deficient carbon atom
• amines can accept a proton, therefore they qualify as a base
• amines react with acids to form ionic salts
• when amines react with acids, they form ionic crystals which crystallise as the water evaporates
• relatively insoluble amines will dissolve in acid because they form ionic salts
• adding a strong base to a mixture of the ionic salts and water formed by adding an amine to an acid will remove the proton from the salt and regenerate the insoluble amine
• strength of a base depends on how readily it accepts a proton
• the inductive effect is how a group affects the electron density around it, either pulling it towards itself or pushing it away from itself
• alkyl groups release electrons away from themselves towards the nitrogen atom, making the lone pair on the atom more available to attract a proton as it has higher electron density
• aryl groups withdraw electrons towards themselves away from the nitrogen atom, making the lone pair on the atom less available to attract a proton as it has lower electron density
• the order of increasing base strength is:

  arylamines, ammonia, alkylamines
• arylamines are weaker bases than ammonia because of the negative inductive effect
• alkylamines are stronger bases than ammonia because of the positive inductive effect
• primary alkylamines are weaker bases than secondary alkylamines because secondary have twice the positive inductive effect
• tertiary alkylamines are weaker bases than secondary alkylamines because they are insoluble in water
• aromatic amines = amines with a benzene ring

  aliphatic amines = amines with an alkyl group
• halogenoalkanes react with ammonia to produce primary amines
• the process of halogenoalkanes reacting with ammonia is nucleophilic substitution
• when halogenoalkanes are added to ammonia:

  • primary amines are formed
  • primary amines + ammonia form secondary amines
  • secondary amines + ammonia form tertiary amines
  • tertiary amines + ammonia form quaternary ammonium salts
• the mixture produced when halogenoalkanes react with ammonia is made up of primary amines, secondary amines, tertiary amines and quaternary ammonium salts
• the process of adding ammonia to halogenoalkanes to get a specific primary amine is inefficient because a mixture is produced and this is hard to separate, though can be done by fractional distillation
• to get a large yield of primary amine when mixing halogenoalkanes and ammonia, use an excess of ammonia
• amines react with acyl chlorides/acid anhydrides to produce N-substituted amides
• the process of amines reacting with acyl chlorides/acid anhydrides is addition-elimination, the same as nucleophilic substitution
• amine + acyl chloride -> n-substituted amide + hydrochloric acid
• amine + acid anhydride -> n-substituted amide + carboxylic acid
• it is better to produce amines by reducing nitriles than by reacting halogenoalkanes with ammonia, because the atom economy for nitriles is high as only one product is made, and the atom economy for halogenoalkanes is low as an impure mixture of products is made