amines

what is a primary amine? (2)

• a primary amine has one carbon atom bonded to the nitrogen atom

• represented as RNH₂

provide an example of a primary amine (1)

CH₃NH₂

what is a secondary amine? (2)

• a secondary amine has two carbon atoms bonded to the nitrogen atom

• represented as R₂NH

provide an example of a secondary amine (1)

(CH₃)₂NH

what is a tertiary amine? (2)

• a tertiary amine has three carbon atoms bonded to the nitrogen atom

• represented as R₃N

provide an example of a tertiary amine (1)

(CH₃)₃N

what is a quaternary ammonium salt? (2)

• a quaternary ammonium salt has four carbon atoms bonded to the nitrogen atom

• represented as R₄N⁺

provide an example of a quaternary ammonium salt (1)

(CH₃)₄N⁺

draw the general structure of quaternary ammonium salts (3)

what property allows primary, secondary, and tertiary amines to act as bases? (1)

the nitrogen atom has a lone pair, which can accept a proton, allowing them to act as bases

how does the availability of the lone pair affect the strength of amines as bases? (2)

• the strength of amines as bases increases

• with the availability of the lone pair on nitrogen for protonation

how do amines and ammonia behave as bases in water? (2)

• they partially dissociate in water

• for example: NH₃ + H₂O ⇌ NH₄⁺ + OH^-

arrange the following in increasing base strength: aromatic amines, ammonia, aliphatic amines (1)

aliphatic amines > ammonia > aromatic amines

why are aromatic amines weaker bases? (3)

• the lone pair on nitrogen overlaps with the delocalised ring

• this makes the lone pair on nitrogen less available

• this is called the negative inductive effect

why are aliphatic amines stronger bases? (3)

• the R group pushes electrons towards the nitrogen atom

• this makes the lone pair on nitrogen more available

• this is called the positive inductive effect

why can amines act as nucleophiles? (1)

they can donate their lone pair of electrons to a δ+ carbon

why do quaternary ammonium salts not react? (1)

they have no lone pair on the nitrogen atom

why are short-chain amines soluble in water? (1)

because they form hydrogen bonds with water molecules

what is the shape of an amine molecule and why? (2)

• amines are pyramidal in shape

• due to three bonding pairs and one lone pair of electrons

what is the shape of quaternary ammonium salts? (1)

tetrahedral

why do amines generally have lower boiling points than alcohols with the same carbon chain length? (2)

• amines have weaker hydrogen bonds compared to alcohols

• resulting in lower boiling points

what are the two methods for preparation of aliphatic amines? (2)

1. nucleophilic substitution of haloalkanes

2. reduction of a nitrile

what is the general equation and conditions for the preparation of amines by nucleophilic substitution of haloalkanes? (1)

RX + 2NH₃ → RNH₂ + NH₄X

• with excess of concentrated ammonia and dissolved in ethanol

what is the general mechanism for the preparation of amines by nucleophilic substitution of haloalkanes? (1)

what is the primary disadvantage of using nucleophilic substitution of haloalkanes for producing aliphatic amines? (2)

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

• resulting in a low yield of primary amine

what are the steps in the 2-step method for producing an amine from reduction of a nitrile?

1. formation of a nitrile from a haloalkane

2. reduction of a nitrile to form an amine

what is the general equation for the formation of a nitrile from a haloalkane? (2)

RX + KCN → RCN + KX

• (nucleophilic substitution in aqueous ethanol)

what is the general equation for the reduction of a nitrile to from an amine? (2)

RCN + 2H₂ → RCH₂NH₂

• (catalytic hydrogenation)

which catalyst and conditions are required in the reduction of nitriles to amines? (1)

nickel catalyst and heat

why does the 2-step method for producing amines yield a purer product compared to the 1-step method? (1)

it increases the length of the carbon chain and reduces the formation of by-products

why can’t phenylamine be made by the reaction of bromobenzene with ammonia? (3)

• the carbon atom bonded to the halogen is in the delocalised ring

• so nucleophiles wont be attracted to it

• benzene ring repels nucleophiles as high electron density

what are aromatic amines/arenes? (1)

they contain a benzene ring

how are aromatic amines formed? (2)

• by the reduction of nitrobenzene

• using HCl and tin as the catalyst

write the balanced equation for the reduction of nitrobenzene to aromatic amines (1)

C₆H₅NO₂ + 6[H] → C₆H₅NH₂ + 2H₂O

what happens to the product of nitrobenzene reduction in the presence of HCl? (1)

• the aromatic amine reacts with HCl

• to form a salt, C₆H₅NH₃Cl

how is the free aromatic amine liberated from its salt? (2)

• by adding sodium hydroxide (NaOH)

• resulting in C₆H₅NH₂ + H₂O + NaCl

write the balanced equation for the liberation of free aromatic amine from its salt (1)

C₆H₅NH₃Cl + NaOH → C₆H₅NH₂ + H₂O + NaCl

write the equation for what happens when ammonia reacts as a base with a proton (1)

NH₃ + H⁺ → NH₄⁺

what is the reaction of phenylamine with H⁺? (1)

C₆H₅NH₂ + H⁺ → C₆H₅NH₃⁺

what is formed when amines react with acyl chlorides? show the general equations by drawing the organic compounds (4)

• an amide and HCl

• then further reaction of second molecule of amine reacts with HCl to form a salt

what is the general mechanism for the acylation of amines?

what is formed when amines react with acid anhydrides? (2)

• an amide and a carboxylic acid

• then further reaction of second molecule of amine reacts with carboxylic acid to form a salt

what are amines used for in the manufacture of synthetic materials? (1)

used in the manufacture of nylon, dyes, and drugs

what are quaternary ammonium salts used for? (1)

as cationic surfactants in fabric softening and hair products

how do quaternary ammonium salts function in hair conditioners? (2)

• they attract to the negative charges on wet hair surfaces

• forming a coating that prevents static electricity and flyaway hair

why are quaternary ammonium salts effective as fabric softeners? (1)

they keep the fabric surface smooth by preventing the build-up of static electricity