Amines

Naming 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. The IUPAC version of the same chemical is propan-1-amine. (This is used in the same way as naming alcohols) If there is another priority functional group as well as the amine group then propylamine the prefix amino is used. Or propan-1-amine 2-aminopropanoic acid. H3C CH C O O H H2N If the amine is secondary and has two alkyl groups attached to the nitrogen, then each chain is named and the smaller alkyl group is preceded by an –N which plays the same role as a number in positioning a side alkyl chain CH3CH2CH2NHCH3 N-methylpropylamine (common name) N-methylpropan-1-amine (IUPAC name) Diethylamine (common name- does not use N if chains are same length) N-ethylethanamine (IUPAC name does still use N) H3C CH2 NH CH2 CH3 In the common naming version if the chain lengths are the same an –N is not used CH3CH2CH2 N CH3 CH3 If a tertiary amine similar rules apply, and each alkyl side group is given an N N,N-dimethylpropylamine (common name) N,N-dimethylpropan-1-amine (IUPAC name) N H (CH2 )6 N H H H It could also be named 1,6-diaminohexane hexane-1,6-diamine 6.2.1 Amines CH3NH2 +H2O
CH3NH3 + +OHNH3 (aq) +H2O (l)
NH4 + (aq) +OH- (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 H+ and so accepting a proton. 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. 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 N is less able to accept protons. Base Properties NH2 phenylamine Amines as bases react with acids to form ammonium salts. CH3NH2 (aq) +HCl (aq)
CH3NH3 +Cl- (aq) Methylamine methylammonium chloride Addition of NaOH to an ammonium salt will convert it back to the amine 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. Reactions with acids CH3CH2NH2 + H2SO4
(C2H5NH3 + )2SO4 2– CH3CH2NH2 + CH3COOH
(C2H5NH3 + ) CH3COO–

Nucleophilic properties Primary amines can be formed by the nucleophilic substitution reaction between haloalkanes and ammonia. CH3CH2Br + 2NH3
CH3CH2NH2 + NH4Br Reaction with ammonia forming primary amine Excess Ammonia dissolved in ethanol is the reagent 3CH C H H Br 3HN: H3C C H H NH3 + Br – In the first step of the mechanism the nucleophile attacks the haloalkane to form an intermediate H3C C H H NH2 + H :NH3 In the second step of the mechanism a second ammonia removes a proton from the intermediate (acts as base) to form the amine H3C C H H NH2 + NH4Br N Goalby chemrevise.org Using an excess of Ammonia can limit further substitution reactions and will maximise the amount of primary amine formed The same reaction mechanism occurs with the secondary amine reacting to form a tertiary amine Reacting primary amines with haloalkanes forming secondary amine Amines will react with haloalkanes in the same nucleophilic substitution reactions that ammonia does above 3CH C H H 2CH Br 3CH2NH2 H3C CH2 NH CH2 CH3 Diethylamine H3C C H H H3C CH2 NH CH2 CH3 Br H3C CH2 N CH2 CH3 CH2 CH3 triethylamine + + CH3CH2NH3 +BrA primary amine will react with a haloalkane to form a secondary amine Reacting secondary amines with haloalkanes to form a teritary amine + H3C CH2 NH2 + CH2 CH3

Reducing nitroarenes to aromatic amines The nitro group on an arene can be reduced an amine group as follows Reagent: Sn and concentrated HCl Conditions: Heating Mechanism:reduction NO2 NH2 + 6[H] As the reaction is carried out in HCl the salt C6H5NH3 +Cl- will be formed. Reacting this salt with NaOH will give phenylamine. phenylamine nitrobenzene + 2H2O