amines

Question 1

what are aliphatic amines?

Answer 1

amines containing aliphatic - R groups, such as alkyl chains

Question 2

what are aromatic amines?

Answer 2

• same general formula as aliphatic amines but aromatic amines must have an aromatic -R group.

Question 3

describe the nature of amines

Answer 3

• organic compounds that contain nitrogen

- can be aliphatic or aromatic

Question 4

what are amides?

Answer 4

organic compounds with functional group:

• RCONH2
• a derivative of carboxylic acid

Question 5

what are primary amines?

Answer 5

• contain 1 -R group and 2 -H groups

- NRH2

Question 6

what are secondary amines?

Answer 6

• contain 2 -R groups and 1 -H group

- NR2H

Question 7

what are tertiary amines?

Answer 7

• conatin Three -R groups and no -H groups

- NR3

Question 8

describe the nature of ammonium ions?

Answer 8

• possibility for fourth group (H+) to be added to ammonia through dative covalent bonding
• because of the lone pair on N
• found as ammonium salts because ion much more stable in this form

Question 9

how can ammonium ions be stabilised?

Answer 9

-by using counter-ion to form salt

Question 10

what is an amine?

Answer 10

• compound based on ammonia where hydrogen atoms have been replaced by alkyl or aryl groups

Question 11

what behaviours do amines show?

Answer 11

• nucleophile

- base

Question 12

what type of base are amines?

Answer 12

weak bases

Question 13

why are amines bases?

Answer 13

• amines contain a lone pair of electrons
• makes amine attracted to positive charge
• gives them basic property of being able to ‘accept protons’

Question 14

what determines amines strength of basicity?

Answer 14

• availability of electrons

- if molecule’s electron pair is more available, it’ll be a stronger base

Question 15

what determines the availability of electrons on amines?

Answer 15

• whether -R groups push or pull electron density

lone pair of electrons more available if electron density is higher

Question 16

describe why primary aliphatic amines are stronger bases than ammonia, which is a stronger base than aromatic amines

Answer 16

aromatic amines:

• benzene ring draws electrons towards itself and the nitrogen lone pair gets partially delocalised onto the ring
• so electron density on nitrogen decreases, making the lone pair much less available

1y aliphatic amine:
- alkyl groups push electrons onto attached groups. So the electron density on the N atom increases. Makes lone pair more available

Question 17

what does the lone pair of electrons on the amines mean for the amines?

Answer 17

• they’re nucleophiles
• react with halogenoalkanes in a nucleophilic substitution
• or with acyl chlorides and acid anhydrides in nucleophilic addition-elimination reactions

Question 18

uses of quaternary ammonium salts?

Answer 18

• quarternary ammonium salts with at least 1 long hydrocarbon chain used as cationic surfactants
• hydrocarbon tail will bind to non-polar substances (like grease, oils + fats)
• whilst cationic head (hydrophillic) will dissolve in water, so useful for fabric cleaners and hair products
• in addition, (ammonium ion) will bind to negatively charged surfaces such as hair and fibre. this gets rid of static, so theyre often used in fabric conditioners

Question 19

state two ways aliphatic amines can be made

Answer 19

• heating halogenoalkane with excess ammonia

- reducing a nitrile

Question 20

describe what addition of an alkyl group does to an amine and so what is the order of strength of basicity of amines?

Answer 20

• alkylated amines more basic than ammonia
• and alkyl -R group will increase basicity
• alkyl -R groups push electron density towards the N
• increases electron density on nitrogen, making lone pair more available so:
  3y>2y>1y>NH3>aromatic amine

Question 21

describe the ‘positive inductive effect’ on methylamine as an example

Answer 21

• H atom is slightly more electropositive than C atom
• means C atom has a slight surplus of electrons which N atom can attract towards itself
• effect known as a “positive inductive effect” and it means N atom has an excess of electron density

Question 22

conditions for halogenoalkane with excess ammonia and equation

Answer 22

• haloalkane with excess conc. ammonia dissolved in ethanol
• pressure in a sealed container
  NH3 + CH3Cl —> CH3NH2 + HCl

Question 23

Order these in order of how basic they are, starting with the weakest base:
Meythl amine, phenyl amine, Ammonia

Answer 23

• Phenyl amine, Ammonia, Methyl amine

Question 24

Why are alkyl amines the most basic?

Answer 24

• positive induction effect from the carbon chain makes the lone pair on the nitrogen more available for protons

Question 25

mechanism name for reaction of halogenoalkanes with ammonia

Answer 25

nucleophilic substitution

Question 26

outline mechanism with halogenoalkane and ammonia

Answer 26

- ammonia attacks carbon in halogenoalkane - halogen released - a second ammonia molecule donates its lone pair of electrons to a hydrogen (which stabilised positive charge on N), which breaks off from the alkylammonium salt - so primary amine and ammonium salt formed

Question 27

what is an issue with the production of primary amines by haloalkanes and ammonia? and how can it be solved?

Answer 27

- primary amine produced is a nucleophile (it has a LP of electrons) - so it can react with remaining haloalkane in further nucleophilic substitution reactions, making secondary and tertiary amines and quarternary amines solution: use large excess of ammonia so primary amine is main product - more ammonia so haloalkane more likely to react with that than a primary amine

Question 28

describe the type of bonding present in amines

Answer 28

H bonding between molecules - liquid at room temp - weaker than in alcohols (No H bonding between tertiary amine molceules - as no H attached to N)

Question 29

conditions of forming an amine by reduction of nitrile

Answer 29

- KCN, warm ethanol and then LiAlH4 in ethoxyethane | - (catalytic hydrogenation) Nickel or platinum catalyst, high temp and pressure

Question 30

describe the reduction of a nitrile to produce a primary amine

Answer 30

- use LiAlH4 (strong reducing agent) in a non-aqueous solvent (e.g. dry ether) followed by some dilute acid - LiAlH4 too expensive for industrial use so: nitrile reduced using H gas with metal catalyst like platinum or nickel at high temp and pressure (catalytic hydrogenation) R-CH2-C-N + 2H2 ---> R-CH2-CH2NH2

Question 31

What are the advantages and disadvantages of forming an amine through the reduction of a nitrile?

Answer 31

- More efficient than reacting a haloalkane with ammonia as there are no side products - However there are 2 steps so there will be percentage yield loss between reactions - KCN is very toxic

Question 32

write out reduction of nitrile general equations in the forming of primary amines

Answer 32

R-X + KCN --> (warm ethanol) R-C(x3 bond)N + KX in R-C(x3 bond) + 4[H] ---> (LiAlH4) in ethoxyethane ---> R-CH2-NH2 in short: R-CN + 4[H] -> R-CH2-NH2

Question 33

suggest one reason why phenylamine cannot be prepared from bromobenzene in a similar way (nucleophilic substitution)

Answer 33

- lone pair of electrons on ammonia will be repelled by electron density of bromobenzene

Question 34

How do you make aromatic amines? Outline the process

Answer 34

(1) heat mixture of a nitro compound, tin metal and conc. HCl under reflux - makes a salt (2) turn salt into aromatic amine, add an alkali such as NaOH solution

Question 35

What are the uses of aromatic amines?

Answer 35

Dyes

Question 36

What are the products and mechanism for when an amine reacts with an acyl chloride?

Answer 36

Nucleophillic addition/elimination | alkyl ammonium salt and amide

Question 37

products of the reaction of halogenoalkane with ammonia

Answer 37

- primary amine and an ammonium salt

Question 38

products of the reaction of halogenoalkane with a primary or secondary amine

Answer 38

alkyl-substituted amine and halogen acid

Question 39

how is a secondary amine made from a primary amine?

Answer 39

- nucleophilic substitution (same mechanism as NH3 with halogenoalkane) - electrons on nitrogen of 1y amine attack delta positive carbon - carbon-halogen bond breaks, halogen leaves as ion and primary amine joins on, nitrogen now has a positive charge - ammonia molecule attacks hydrogen and neighboring hydrogen stabilizes positive nitogen and hydrogen breaks off, forming ammonium ion with ammonia molcule

Question 40

which is a stronger base, ammonia or cyclohexylamine?

Answer 40

- cyclohexylamine is a primary amine compared to ammonia - cyclohexylamine has a greater electron density on Nitrogen lone pair - cyclohexylamine has a greater ability to accept H+