5.4.2 THE AMINES Nomenclature

Smell: Methylamine and ethylamine smell like ammonia - as the chains getbigger, the smell becomes fishy, or like B.O..

Primary, Secondary and TertiaryAmines

PhysicalProperties

Hydrogen bonding is present between primary and to a lesser extent secondary amines. The longer the carbon chain, the greater the London forces

Solubility in water

The small amines of all types are very soluble in water.

Amines can form hydrogen bonds with water…

Solubility decreases significantly after about 6 carbons. The hydrocarbon chains interfere with the hydrogen bonds between water molecules.

Water soluble amines produce an alkaline solution. Write the eqn…NB. Amines produce solutions with a higher pH than a solution of ammonia for a givenconcentration. The exception is phenylamine – see later.

Amines asbases

Write the equation for the reaction of ethylamine with hydrochloric acid…

Name the salt formed.What is salting out (p210)?

Copper (II) Complexes

Remember the reaction between copper(II) ions and ammonia?…

Inexcess…

Small amines behave in the sameway…

The blue colours are similar. For longer amines, both the colour and the number of ligands will change due to steric effects.

Reactions with acylchlorides

Concentrated methylamine solution and ethanoyl chloride reacted vigorously in the cold…

N-methylethanamide and methylammonium chloride are formed

How could we make paracetamol?

Amines with Halogenoalkanes

PHENYLAMINE

(aminobenzene or, in the past, aniline).

Preparation*:It is not possible to substitute the chlorine inchlorobenzene, due to the interaction betweena lone pair of electrons on the chlorine and thedelocalised pi system of the benzene(increasing the C-Cl bond strength).

The movement of electrons away from thechlorine towards the ring makes the moleculeless polar than you would otherwise haveexpected.

First, nitrobenzene is prepared as outlined above. Then this is reduced to phenylamine

Reagents: tin and concentrated hydrochloric acid.

Conditions: The mixture is heated under reflux in a boiling waterbath for about half an hour.C6H5NO2 + 6H+ + 6e- C6H5NH2 + 2H2O

Sn + 6Cl- SnCl62- + 4e-

Mole ratio Sn: C6H5NO2 ??The large quantities of NaOH required to neutralise the excessconcentrated acid make this process uneconomic on anindustrial scale.

Phenylamine is a weak base because of the interaction of the lone pair with the π system of the ring (see below)

Although it is only very slightly soluble in water*,…

phenylamine reacts with acids like hydrochloric acid in exactly thesame way as any other amine. A solution of a salt is formed -phenylammonium chloride.

This is a convenient form to comercialise phenylamine, and thepure product can be recovered by adding alkali…

*the pH is lower than an equivalent solution of an aliphatic amine or ammonia. This isdue to the interaction of the lone pairs on the N with the ring. They are less available

The donation of the nitrogen's lone pair into the ring system increases the electron density around the ring. That makes the ring much more reactive than it is in benzene itself.

N-phenylethanamide

Other derivatives: The reactions with acyl chlorides

(phenylamine acts as a nucleophile).

Questions, p212

Nitrous acid

The pale blue, unstable nitrous acid results, which reacts withaliphatic and aromatic amines in different ways.

Phenylamine reacts with nitrous acid differently depending on thetemperature.If the temperature is higher than 5ºC…

The reaction is similar to the one above and phenol is produced.

Nitrous acid (also known as nitric(III) acid) has the formula HNO2 and ismade by dissolving sodium nitrite in dilute hydrochloric acid.

If the solution of phenylamine in hydrochloric acid (phenylammoniumchloride solution) is stood in a beaker of ice, and a cooled solution ofsodium or potassium nitrite solution is then added very slowly,(temperature < 5°C) the product is a solution containingbenzenediazonium chloride:

The positive ion, containing the -N2+ group, is known as a diazonium ion ( the "azo" refers to nitrogen). Diazonium salts are very unstable.

The formation of the diazonium ion is called diazotisation.

Coupling reactions of

diazonium ions:

The reaction with (cold alkaline) phenol

The product is one of the simplest of what are known as azo compounds, in which two benzene rings are linked by a nitrogen bridge. They are very colourful.Questions, p218

(4-hydroxyphenyl)azobenzene

Revision: Unit 4

General case

The ethanoyl chloride is carefully added to XS concentrated ammonia soluntion…

Read pp213-215 and outline the manufacture of paracetamol

Context Study: The pharmaceutical industry

Condensation Polymerisation

A simple polyester - Terylene

The monomers

Draw the repeating unit...

POLYAMIDES – MORE CONDENSATION POLYMERISATION

The amide link

Draw the repeating unit...

The ring breaks to give a repeatingunit that contains only 6 C atoms...

Kevlar

Repeating unit...

AdditionPolymerisation

The percentage of acid groupswhich have been removed in theproduction process influences thestrengths of the intermolecularforces upon which the solubilitydepends. Different solubilities givethe plastic different uses, eg.Soluble stitches, laundry bags,detergent bags.

2-propenamide (acrylamide)

Represent the addition polymerisation reaction...

Used in contact lenses. Why?

AMINOACIDS

The Ninhydrin Reaction

Common alpha-amino acids, except proline, undergo a unique reaction with thetriketohydrindene hydrate - ninhydrin. Among the products is a purple colored iminoderivative, which provides as a useful color test for these amino acids, most of whichare colorless.

A common application of the ninhydrin test is the visualization of amino acids in paperchromatography. Samples of amino acids or mixtures thereof are applied along a linenear the bottom of a rectangular sheet of paper (the baseline). The bottom edge of thepaper is immersed in an aqueous buffer, and this liquid climbs slowly toward the topedge.

Questions, p226/230

As the solvent front passes the sample spots, thecompounds in each sample are carried along at a ratewhich is characteristic of their functionality, size andinteraction with the cellulose matrix of the paper.

Some compounds move rapidly up the paper, while othersmay scarcely move at all. The ratio of the distance acompound moves from the baseline to the distance of thesolvent front from the baseline is defined as the retardation(or retention) factor Rf.

Different amino acids usually have different Rf's undersuitable conditions. In the example on the right, the threesample compounds (1, 2 & 3) have respective Rf values of0.54, 0.36 & 0.78.