3.3.11.3 nucleophilic properties

what can amines act as?

as nucleophiles

name the mechanism haloalkanes undergo to form amines

nucleophilic substitution

what is the condition to form amines with haloalkanes?

excess ammonia

outline the products that can be formed from a reaction between ammonia + amines with haloalkanes

this reaction can form primary, secondary, tertiary amines and quaternary ammonium salts

eg for the reaction between bromoethane + excess ammonia, give the symbol equation

CH₃CH₂Br + 2NH₃ → CH₃CH₂NH₂ + NH₄Br (quaternary ammonium salt)

draw the mechanism for eg excess ammonia and 1-bromopropane

draw the mechanism + give the symbol equation for eg excess ammonia and 1,3 - dichloroopropane

outline the disadvantage of nucleophilic substitution of haloalkanes as a method of preparing amines

• a mixture of amine products is formed due to the product also acting as a nucleophile

• therefore a LOW YIELD of primary amine is produced due to further substitution

• other products include secondary, tertiary amines + quaternary ammonium salts

how can you minimise these further substitutions?

by using a large excess of ammonia as this would make ammonia more likely to react as the nucleophile

outline what further substitution is

the amine product can also react with the halogenoalkane, as the N has its lone pair of electrons + can behave as a nucleophile → this leads to a mixture of haloalkanes being produced

outline the 4 stages/reactions that can take place with ammonia + bromomethane

• stage 1: reaction between a halogenoalkane + ammonia produces the primary amine

• stage 2: primary amine produced has a lone pair on N + can behave as a nucleophile

• stage 3: secondary amine produced can also react with another halogenoalkane to produce a tertiary amine

• stage 4: tertiary amine also has a lone pair on N, therefore further substitution is possible, which leads to quaternary ammonium salt

give the equation + draw the mechanism for stage 1 (between ammonia + bromomethane)

give the equation + draw the mechanism for stage 2 (between ammonia + bromomethane)

give the equation + draw the mechanism for stage 3 (between ammonia + bromomethane)

give the equation + draw the mechanism for stage 4 (between ammonia + bromomethane)

a. what does a large excess of halogenoalkane lead to?

b. what does a large excess of ammonia lead to?

a. high yield of quaternary ammonium salt

b. better yield of primary amine

give the basic structure of quaternary ammonium salts

• the R groups are carbon chains → they are likely to be the same but can be different

what are quaternary ammonium salts used as?

as cationic surfactants

how are quaternary ammonium salts formed?

from excess halogenoalkanes + ammonia or amines

outline the changes that occurs to the reactants to form quaternary ammonium salts

• any carbon chains on the nitrogen at the start of the reaction will remain on the nitrogen

• all hydrogens directly bonded to the nitrogen are removed + extra carbon chains will be added from the halogenoalkanes until there are four carbon chains around the nitrogen

• the X- will be the halide from the halogenoalkane

give the structure of the quaternary ammonium salt formed from methylamine + excess chloroethane

CH₃N(CH₂CH₃)₃⁺Cl⁻

ethylamine reacts with an excess of 1-bromopropane, what is the final product?

CH₃CH₂N(CH₂CH₂CH₃)₃⁺Br⁻

outline what amines are used in

in the manufacture of synthetic materials such as nylon, dyes + drugs

what are quaternary ammonium salts used as?

as cationic surfactants in fabric softening + hair products