7.5 Amines

Question 1

What are Amines ?

Answer 1

Question 2

Properties of Amines ?

Answer 2

Question 3

Preparation of Aliphatic Amines (1)

Answer 3

Question 4

Preparation of Aliphatic Amines (2)

Answer 4

Question 5

Preparation of Primary Aromatic Amines

Answer 5

Question 6

NUCLEOPHILIC PROPERTIES/REACTIONS OF AMINES

Answer 6

Question 7

NUCLEOPHILIC SUBSTITUTION REACTIONS

Answer 7

Question 8

USES OF QUATERNARY AMMONIUM SALTS

Answer 8

Question 9

NUCLEOPHILIC ADDITION-ELIMINATION REACTIONS

Answer 9

Question 10

AMINES AND AMIDES NOMENCLATURE

Answer 10

Question 11

BASE PROPERTIES OF AMINES

Answer 11

Question 12

DIFFERENCES IN BASE STRENGTHS

Answer 12

Question 13

REACTIONS AS BASES

Answer 13

Question 14

Give an equation for the preparation of 1,6-diaminohexane by the reaction of
1,6-dibromohexane with an excess of ammonia (2)

Answer 14

Br-(CH2)6–Br + 4 NH3 → H2N-(CH2)6–NH2 + 2 NH4Br

Question 15

1,6-Diaminohexane can also be formed in a two-stage synthesis starting from
1,4-dibromobutane.
Suggest the reagent and a condition for each stage in this alternative synthesis (3)

Answer 15

•   M1 Stage 1 reagent KCN or NaCN
•   Stage 1 condition aqueous alcohol
•   Stage 2 reagent & condition H2 and Ni or Pt or Pd

Question 16

Explain why 3-aminopentane is a stronger base than ammonia (3)

Answer 16

• In 3-aminopentane
• Lone pair on N more available or Lone pair on N accepts H+ better
• because of alkyl electron pushing /inductive effect

Question 17

Justify the statement that there are no chiral centres in 3-aminopentane (1)

Answer 17

No carbon (atom is) attached to 4 different groups

Question 18

(6)

Answer 18

• (Strength depends on availability of) lone pair on N (atom)
• E N (next to ring): (lp) delocalised into ring
• (lp) less available (to donate to or to accept a H+)
• F or G: N (next to alkyl): (positive) inductive effect/electrons pushed to N
• p) more available (to donate to or to accept a H+)
• order of increasing base strength E<G<F

Question 19

Amine F can be prepared in a three-step synthesis starting from methylbenzene.
Suggest the structures of the two intermediate compounds.
For each step, give reagents and conditions only. Equations and mechanisms are not
required (3)

Answer 19

Question 20

Butylamine can also be prepared in a two-step synthesis starting from 1-bromopropane,
CH3CH2CH2Br. Write an equation for each of the two steps in this synthesis (3)

Answer 20

• CH3CH2CH2Br + KCN → CH3CH2CH2CN + KBr balanced
• CH3CH2CH2CN + 2H2 → CH3CH2CH2CH2NH2

Question 21

Explain why butylamine is a stronger base than ammonia (2)

Answer 21

• Lone pair (on N) (in correct context)
• R group increases electron density / donates electrons /pushes electrons / has positive inductive effect

Question 22

Identify a substance that could be added to aqueous butylamine to produce a basic buffer solution (3)

Answer 22

• Any strong acid (but not concentrated)
• or any amine salt or ammonium salt of a strong acid

Question 23

Outline a mechanism for the formation of ethylamine from bromoethane. State why the
ethylamine formed is contaminated with other amines. Suggest how the reaction conditions
could be modified to minimise this contamination (6)

Answer 23

Question 24

Suggest one reason why phenylamine cannot be prepared from bromobenzene in a similar
way. Outline a synthesis of phenylamine from benzene. In your answer you should give
reagents and conditions for each step, but equations and mechanisms are not required (6)

Answer 24

Question 25

Answer 25

* M1 CH3NH2 Shown as displayed or abbreviated structural formula * M2 N-methyl ethylamine or N-methyl ethanamine

Question 26

Answer 26

Question 27

Answer 27

* **M1** The lone pair on nitrogen in P is more available or more able to accept protons/H+ * **M2** More alkyl groups are electron releasing/donating **OR** greater (positive) inductive effect (of the alkyl groups)

Question 28

State the reagent and reaction conditions needed for reaction 3. Give an equation for reaction 3 (2)

Answer 28

* **M1** H2 and Ni/Pt/Pd * **M2** NCCH2CH2CN + 4H2 → H2N(CH2)4NH2

Question 29

Primary amines can be prepared by the reaction of halogenoalkanes with ammonia or by the reduction of nitriles. **Justify** the statement that it is better to prepare primary amines from nitriles rather than from halogenoalkanes (3)

Answer 29

* With halogenoalkane: urther reaction (of primary amines) * **OR** mpure product/mixture of products/lower atom economy * With nitriles nofurther reaction * **OR** Simple product / higher atom economy

Question 30

A student dissolves a few drops of propylamine in 1 cm3 of water in a test tube. Give an equation for the reaction that occurs. Describe what is observed when Universal Indicator is added to this solution (2)

Answer 30

* CH3CH2CH2NH2 + H2O ⇌ CH3CH2CH2NH3 + + OH– * (green) turns blue

Question 31

Answer 31

Question 32

How can Primary aliphatic amines act as Bronsted-Lowry bases ?

Answer 32

* 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 * They are weak bases as only a low concentration of hydroxide ions is produced

Question 33

Amine reactions with **acids** :

Answer 33

Question 34

How can a **basic buffer** be made from an amine ?

Answer 34

* Basic buffers can be made from combining a weak base with a salt of that weak basee.g. Ammonia and ammonium chloride * Methylamine and methylammonium chloride * Ethylamine and ethylammonium chloride

Question 35

Preparing amines from nitriles in a 2 step reaction

Answer 35

Question 36

Reducing nitroarenes to aromatic amines

Answer 36

Question 37

Other reactions of amines

Answer 37

Question 38

Draw the structure of the species formed when serine reacts with dilute hydrochloric acid (1)

Answer 38

Question 39

Draw the structure of the species formed when serine reacts with an excess of bromomethane (1)

Answer 39

Question 40

Answer 40

* (As a) soap * (Bio)diesel or biofuel or fuel for cars/lorries * (Cationic) surfactant /detergent /fabric softener /germicide / shampoos / (hair) conditioners /spermicidal jelly

Question 41

# **ChemRevise Notes** Base Properties of Amines

Answer 41

Question 42

How are Secondary amines are stronger bases than primary amines ?

Answer 42

they have more alkyl groups that are substituted onto the N atom in place of H atoms. Therefore more electron density is pushed onto the N atom (as the inductive effect of alkyl groups is greater than that of H atoms), so making the lone pair of electrons on the nitrogen more readily available.

Question 43

Base strength of **aromatic amines**

Answer 43

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 lone pair on the N is less able to accept protons

Question 44

Amine Reactions with **Acids**

Answer 44

Question 45

Making a basic buffer from an amine

Answer 45

Basic buffers can be made from combining a weak base with a salt of that weak basee.g. Ammonia and ammonium chloride Methylamine and methylammonium chloride Ethylamine and ethylammonium chloride

Question 46

Overall scheme of reactions (Amine formation from halogen reactions)

Answer 46

Question 47

Preparing amines from **nitriles** in a 2 step reaction

Answer 47

Question 48

Reducing **nitroarenes** to aromatic amines

Answer 48