OCR Chemistry A H432. Amines are described as primary, secondary or tertiary depending on how many carbons are bonded to the N atom.

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1 OCR Chemistry A 432 About amines: can be considered as derivatives of ammonia, with one or more of the atoms replaced by alkyl groups. They are noted for their unpleasant, often fishy odours. We classify aromatic amines as those in which the 2 is bonded directly to a benzene ring, and aliphatic amines as those in which it is not (even if the molecule contains a benzene ring elsewhere). This means a molecule can be aromatic, and an amine, without being an aromatic amine! are described as primary, secondary or tertiary depending on how many carbons are bonded to the atom. Common naturally-occuring amines include amphetamine (used to treat daytime drowsiness and chronic fatigue syndrome), phenylephrine (decongestant in LemSip) and adrenalin. aming amines: For primary amines, when the amine group is on the first carbon of the chain: C 3 C 2 C 2 2 propylamine primary For primary amines when the amine group is elsewhere in the chain: C 3 C 2 C( 2 )C 3 2-aminobutane primary For secondary and tertiary amines with the same alkyl group attached to the : (C 2 5 ) 2 diethylamine secondary (C 3 7 ) 3 tripropylamine tertiary Where two or more different groups are attached to the, it is named as a substituted derivative of the longest chain amine, with the prefix - used to indicate that the other groups are attached to the nitrogen rather than the carbon skeleton. 3 C C 2 C 2 3 C C 3 7 C 3 -methyl propylamine secondary C 3 7 C 2 5 C 2 5,-diethylpropylamine tertiary C 2 3 C C 3 -ethyl--methylphenylamine tertiary Page 1

2 OCR Chemistry A 432 We can also have more than one amine group attached to the chain: 2 (C 2 ) 4 2 1,4-diaminobutane (both amine groups are primary) as bases A base is defined as a proton acceptor. The nitrogen atom in an ammonia molecule and similarly in amines can do this since its lone pair can accept a proton forming a dative bond and becoming an 4 ammonium ion, or alkylammonium ion respectively. The reaction is reversible, and so ammonia and amines are therefore weak bases. C 3 C 3 methylamine methylammonium ion Reactions of amines as bases Since amines are weak bases they will react with acids to form salts. otice that the positive charge should to be on the atom, or the whole ion in square brackets. C 2 C 2 2(aq) Cl (aq)! ethylamine [C 3 C 2 3 ] Cl - (aq) ethylammonium chloride Alkylammonium salts are named based on the acid from which they are formed, just like metal salts and ammonium salts. Aromatic amines react in exactly the same way: 2 O 3! phenylamine nitric acid phenylammonium nitrate Practice: i) Write an equation for the formation of ethylammonium sulphate ii) Write an equation for the reaction of excess dimethylamine with phosphoric acid iii) Write an equation for the reaction of -ethyl--methylamine with ethanoic acid Page 2

3 OCR Chemistry A 432 Preparation of aliphatic amines Making primary aliphatic amines: Starting material: aloalkane Reagent: Ammonia Conditions: Gently warm with excess ammonia using ethanol as solvent. Aqueous alkali is then added to convert the alkylammonium salt to the amine. Type of reaction: ucleophilic Substitution Formation of the alkylammonium salt: C 3 C 2 C 2 Cl 3! C 3 C 2 C 2 3 Cl - 1-chloropropane propylammonium chloride Formation of the amine: C 3 C 2 C 2 3 Cl - ao! C 3 C 2 C 2 2 acl 2 O otes: The use of ethanol as a solvent is in part because amines tend to be insoluble in water and more soluble in ethanol, but mainly to prevent substitution reactions between the haloalkane and the water, producing alcohols. The use of excess ammonia is to ensure that there is a much higher concentration of ammonia in the reaction mixture than the concentration of the product amine. This minimises the formation of secondary amines when the product primary amine, which also has a lone pair on the nitrogen, acts as a nucleophile and attacks another halogenoalkane molecule. C 3 C 2 C 2 2 C 3 C 2 C 2 Cl! (C 3 C 2 C 2 ) 2 Cl.B. Exam questions may include phrases like An additional product is made with (very large) M r which is a clue to consider whether the main product you are forming is itself capable of further reaction. An alternative reaction to form primary amines, which avoids the problem of further substitution of the product, is the reduction of a nitrile group C to an amine C 2 2. This is covered in Topic Carbon-carbon bond formation. Making secondary or tertiary aliphatic amines: The reaction of ammonia with haloalkanes is unsuitable for the production of primary amines because the primary amine reacts further with haloalkanes to make a mixture of secondary and tertiary amines. This gives us a method of producing secondary and tertiary amines. The conditions and type of reaction are the same. C 3 C 2 C 2 Cl C 3 C 2 C 2 2! (C 3 C 2 C 2 ) 2 2 Cl - propylamine dipropylammonium chloride (C 3 C 2 C 2 ) 2 2 Cl - ao! (C 3 C 2 C 2 ) 2 acl 2 O dipropylamine Page 3

4 OCR Chemistry A 432 Similarly a secondary amine can be reacted with a haloalkane to produce a tertiary amine. Making aromatic amines (i.e. amine bonded to benzene ring): Starting material: itroarenes (nitro group on a benzene ring) Conditions: eat under reflux with mixture of tin and conc. hydrochloric acid. eutralise the acid with excess ao when reaction complete Type of reaction: Reduction. The mixture of tin and Cl acts as a reducing agent which we can show as [] for simplicity. tin/conc Cl Equation: O 2 6[]! excess ao(aq) O nitrobenzene phenylamine otes: Remember if there are other groups present alkyl groups that you are only reducing the nitro- group. Extension Material OT O SPECIFICATIO The role of amines in dye-making The history of synthetic dyes is linked to amines. The first synthetic purple dye, mauveine, was made by Sir W.. Perkin in This was the first example of an "aniline dye" since aniline is the trivial name for phenylamine. Another family of dyes are the "azo dyes" and these are also made from aromatic amines. Synthesis of azo-dyes Stage 1: diazotisastion When a mixture of phenylamine and nitrous acid (O 2 ) is reacted below 10 C, a diazonium salt is formed. The diazonium salt is unstable and decomposes if allowed to warm above 10C C. itrous acid is generated in-situ by reacting sodium nitrite (ao 2 ) with hydrochloric acid: ao 2 Cl! O 2 acl The cold nitrous acid then reacts with an aromatic amine such as phenylamime to form a salt containing the diazonium ion: below 10 C O 2 2Cl! 2 2 O 2 Cl - phenylamine nitrous acid benzenediazonium chloride Page 4

5 OCR Chemistry A 432 Stage 2: coupling reaction A coupling reaction occurs when the diazonium salt, benzene diazonium chloride is reacted with a phenol, or another aromatic compound such as an amine, under alkaline conditions. The temperature must remain below 10 C or the diazonium salt decomposes. The two benzene rings become linked through an azo functional group, -=- The azo link is generally formed opposite the O or 2 group, although you may see examples where it has been formed elsewhere on the ring. Cl - O ao (aq) O acl 2 O (4-hydroxyphenyl)azobenzene The product is a brightly coloured compound used as an azo dye. Many different colours can be produced by varying the structure of the azo compound Page 5

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.