Amines. Types of Amines. chemrevise.org. N Goalby Chemrevise.org. primary amine (one C attached to N) H. Secondary amine (two C s.

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1 Amines Goalby hemrevise.org Types of Amines primary amine (one attached to ) Secondary amine (two s attached to ) name : diethylamine It is also possible to have aromatic amines 2 phenylamine name: methylamine tertiary amine (three s attached to ) name: triethylamine 1

2 Basic nature of amines Solubility in water and basic nature. Small amines can form hydrogen bonds with water and therefore can dissolve readily in water. 3 O They also react with the water to form basic solutions. 3 2 (aq) 2 O (l) 3 3 (aq) O - (aq) Primary aliphatic amines act as Bronsted-Lowry Bases because the lone pair of electrons on the nitrogen is readily available for forming a dative covalent bond with a and so accepting a proton Base strength Primary aliphatic amines are stronger bases than ammonia as the alkyl groups are electron releasing and push electrons towards the nitrogen atom and so make it a stronger base. 3 (aq) 2 O (l) 4 (aq) O - (aq) The more alkyl groups that are substituted onto the atom in place of atoms, the more electron density is pushed onto the atom (as the inductive effect of alkyl groups is greater than that of atoms). The more alkyl groups, the higher the electron density of the lone pair on the, so the stronger the base. Therefore 3 o amines are stronger bases than 2 o which are stronger than 1 o amines amines 3 o > 2 o > 1 o > 3 2

Base strength of aromatic amines Primary aromatic amines such as Phenylamine do not form basic solutions because the lone pair of electrons on the nitrogen

2 phenylamine 3 o > 2 o > 1 o > 3 > aromatic Methods of preparing amines Method 1: Preparation from haloalkanes hange in functional group: haloalkane amine Reagent:

3 Base strength of aromatic amines Primary aromatic amines such as Phenylamine do not form basic solutions because the lone pair of electrons on the nitrogen delocalise with the ring of electrons in the benzene ring. This means the is less able to accept protons. 2 phenylamine 3 o > 2 o > 1 o > 3 > aromatic Methods of preparing amines Method 1: Preparation from haloalkanes hange in functional group: haloalkane amine Reagent: 3 dissolved in ethanol onditions: eating under pressure (in a sealed tube) Mechanism: ucleophilic Substitution Type of reagent: ucleophile, : 3 Equation: 3 2 l (l) 2 3 (alc) (l) 4 l (aq) l l 1-chloroethane ethylamine 3

4 ucleophilic substitution mechanism For formation of primary amine from haloalkane δ δ- l - 3 l This reaction does not give a good yield and various other side products are formed l - KEY Further substitution reactions between Amines and haloalkanes 3 2 l (l) 2 3 (alc) (l) 4 l (aq) Primary amine The amine formed in this reaction has a lone pair of electrons on the nitrogen and can also act as a nucleophile and will react further with the haloalkane l diethyl amine Secondary amine l Using an excess of Ammonia can limit this second reaction and will maximise the amount of primary amine formed 4

5 3 2 2 ucleophilic substitution mechanism For formation of secondary amine δ δ- 3 l l diethylamine 4 l - 3 KEY The secondary amine product has a lone pair of electrons and so can also substitute to form a tertiary amine l triethyl amine(3 o ) 3 Br : : triethylamine 5

6 The tertiary amine product has a lone pair of electrons and so can also substitute to form a quaternary ammonium salt l l - Using an excess of the haloalkane will promote the formation of the quaternary salt 2 3 tetraethyl ammonium chloride 3 : Br Tetraethylammonium ion Quaternary salts 3 ( 2 ) 11 3 ( 2 ) 11 ( 2 ) 11 3 ( 2 ) 11 l - 3 Quaternary Salts can be used as cationic surfactants The positive nitrogen is attracted toward negatively charged surfaces such as glass, hair, fibres and plastics. This helps in their uses as fabric softeners, hair conditioners and sewage flocculants 6

7 Some questions will involve substituting an amine onto a haloalkane which has a different length of carbon chain from the amine propylamine 3 Br Br methylpropylamine,-dimethylpropylamine 3 Br 3 Br Trimethylpropyl-ammonium bromide Using excess bromomethane would promote the final quaternary salt Methods of preparing amines 2 Using haloalkanes and ammonia is not an efficient method for preparing primary amines because of the further substitution that occurs. A better method is to use the following two step method Step1: onversion of a haloalkane nitrile Reagent: K dissolved in ethanol onditions: eating under reflux Mechanism: ucleophilic Substitution Type of reagent: ucleophile, : - : - Equation: Br : - Br - 1-bromopropane butanenitrile 7

8 Methods of preparing amines 2 Step 2: Reduction of the nitrile amine Reagents: Mechanism: LiAl 4 dissolved in ether (diethylether) (followed by hydrolysis with water) Reduction Type of reagent: Reducing Agent LiAl 4 Equation: 4[] LiAl 4, in ether then 2 O butanenitrile butylamine A disadvantage of this method is that it is a two step reaction that may therefore have a low yield. Also K is toxic Reducing nitro-arenes to amines The nitro group on an arene can be reduced an amine group as follows Reagent: onditions: Mechanism: Sn and l or Fe and l eating reduction O 2 Sn and l 2 These amines can be converted to other compounds that are used as dyes 8

9 Reaction with acid Amines react with acids to form ammonium salts. 3 2 (aq) l (aq) 3 3 l - (aq) methylammonium chloride Phenylamines react with acid 2 3 phenylammonium ion The ionic salts formed in this reaction means that the compounds are soluble in the acid. e.g. Phenylamine is not very soluble in water but phenylammonium chloride is soluble These ionic salts will be solid crystals, if the water is evaporated, because of the strong ionic interactions. Formation of complex ions The lone pair of electrons on the nitrogen enable amines to act as ligands and bond into transtion metal ions to form coloured complex ions. 4 u( 2 O) u ( 2 O) O Ammonia can also act as a ligand and forms complex ions 4 3 u( 2 O) 6 2 light blue solution [u( 3 ) 4 ( 2 O) 2 ] O deep blue solution 9

6.10 Amines. Naming. N Goalby chemrevise.org 1 CH2 CH2

6.10 Amines. Naming. N Goalby chemrevise.org 1 CH2 CH2 6.10 Amines aming Amines These end in amine. There is, however, rather confusingly two ways of using this suffix. The exam board tend to use the common version where the name stem ends in -yl propylamine.