3.11 Amines

Question 1

Draw the structures of primary, secondary and tertiary amines and a quaternary ammonium ion

Question 2

How do you name amines?

Answer 2

-amine or amino-

Question 3

Why are amines so reactive?

Answer 3

The lone pair of electrons on the nitrogen- due to polar N-H bond

Question 4

What shape are amines around the N? Bond angle?

Answer 4

Trigonal pyramidal, 107 degree due to lone pair on N

Question 5

What kind of intermolecular forces do they have? Why?

Answer 5

Hydrogen bonding due to polar N-H bond and lone pair of electrons on N atom

Question 6

Do amines have intermolecular forces which are stronger than or weaker than alcohols? Why?

Answer 6

Weaker, as N has a lower electronegativity than O —> weaker hydrogen bonding

Question 7

What state are amines at 298K?

Answer 7

Short chains are gases, longer chains are volatile liquids

Question 8

What do they smell of? Why?

Answer 8

Fishy smell - rotting fish/flesh releases di- and triamines

Question 9

Which primary amines are soluble in water/alcohols? Why?

Answer 9

Up to 4 carbon atoms, as they can hydrogen bond to water molecules. After this, non-polarity of hydrocarbon chain makes them insoluble

Question 10

What kind of solvents are most other amines soluble in?

Answer 10

Less or non-polar solvents

Question 11

Solubility of phenylamine? Why?

Answer 11

Not very soluble, due to the non-polarity of the benzene ring - C6H5 cannot form hydrogen bonds

Question 12

How can/when do amines act as bases?

Answer 12

When they bond with a H+ ion

Question 13

How can/ when do amines act as nucleophiles?

Answer 13

When they bond with an electron deficient C atom (donate lone pair from N)

Question 14

Draw a mechanism for the basic action of an amine with water

Answer 14

Slide 30

Question 15

What is the product from the basic action of an amine with water?

Answer 15

RNH3 + - ammonium ion, which forms a salt with an anion

Question 16

Is the product (ammonium ion) soluble in water? Why?

Answer 16

Yes, as it is ionic so is attracted to the polar bonds in H2O

Question 17

How could you regenerate the soluble amine from the ammonium salt?

Answer 17

Add a strong base (NaOH) —> removes H+ ions from ammonium ion

Question 18

In order to be the strongest base, what must a particular amine have (out of a set of amines)?

Answer 18

Greatest electron density around the N atom, making it a better electron pair donor (attracts protons more)

Question 19

What does positive/negative inductive effect mean?

Answer 19

Positive inductive effect = donate electrons, increase density around N
Negative means remove electrons, decrease density around N

Question 20

What effect do alkyl groups have (on electron density and base strength)

Answer 20

Positive inductive effect - increase electron density around N —> stronger base

Question 21

What effect do aryl groups have (on electron density and base strength)?

Answer 21

Negative inductive effect - decrease electron density around N —> weaker base

Question 22

Why are 3^0 amines never good bases

Answer 22

They are insoluble in water

Question 23

Place these in order of base strength (in general): NH3, 1^0 amine, 2 ^0 amine, phenylamine

Answer 23

2 ^0 amine > 1 ^0 amine > NH3 > phenylamine

Question 24

Draw a mechanism for the nucleophilic substitution of NH3 with RCH2Br to form primary amines

Answer 24

Slide 50

Question 25

How can primary amines then form 2 ^0,3 ^0 amines and 4 ^0 ammonium ions?

Answer 25

Multiple substitution; primary amine is a nucleophile that attacks the original haloalkane

Question 26

What are the problems with this method

Answer 26

Not efficient as low yield of 1^0 amine due to multiple substitutions

Question 27

How would you maximise the yield of the primary amine?

Answer 27

Use excess ammonia

Question 28

What type of mechanism is the reaction of a haloalkane with a cyanide ion?

Answer 28

Nucleophilic substitution

Question 29

What conditions does this reaction require? What is the product formed?

Answer 29

Ethanol as a solvent

A nitrile is formed

Question 30

How do you get from a nitrile to a primary amine? (Name of reaction type and reagents/catalysts)

Answer 30

Reduction using nickel / hydrogen catalyst

Question 31

Why is this a purer method of synthesising amines?

Answer 31

Only the primary amine can be formed

Question 32

What conditions are needed to form nitrobenzene from benzene

Answer 32

Concentrated H2SO4 and HNO3 to form the NO2+ ion for electrophilic attack

Question 33

How do you form an ammonium chloride salt from nitrobenzene? What conditions are needed?

Answer 33

Reduce the nitrile using Tin / HCl —> forms an ammonium salt with Cl- ions

Room temperature

Question 34

Equation for the reaction of nitrobenzene —> phenylamine?

Answer 34

C6H5NO2 + 6[H] —> C6H5NH2 + 2H2O

Question 35

What mechanism is used for forming amides from acyl chlorides and amines?

Answer 35

Nucleophilic additon/elimination

Question 36

Draw a mechanism for the reaction of ethanoyl chloride with ethanamine

Answer 36

Slide 74

Question 37

In which industries/products are amines used?

Answer 37

Dyes, nylon, drugs, synthesis of new molecules

Question 38

What are cationic surfactants (used in fabric/hair conditioners)?

Answer 38

Quaternary ammonium salts, with a cation that is charged at one end (N+) and non polar at the other

Question 39

How do cationic surfactants work in fabric/hair conditioner?

Answer 39

Negative charges on the surface of the fabric/hair are attracted to the cation, removing them from the surface; prevents build-up of static electricity and keeps hair flat and fabric smooth

Question 40

How do cationic surfactants sit when placed in water?

Answer 40

Charged end in the water, non polar end sticking out of the water/at the surface