Topic 6 Reactions

Question 1

What are the reagents and conditions needed to convert an alkene to an alkane?

Answer 1

Reagent: Hydrogen
Catalyst: Nickel
Conditions: 150 degrees centigrade and 5 atmospheres.

Question 2

The hydrogenation of a double bond involves which reaction mechanism?

Answer 2

Electrophilic Addition

Question 3

What are the reagents and conditions needed to convert an alkane to a halogenoalkane?

Answer 3

Reagent: Halogen (e.g. Bromine)
Catalyst: None
Conditions: UV light.

Question 4

The conversion of an alkane to a halogenoalkane involves which reaction mechanism?

Answer 4

Free radical substitution

Question 5

In the process of producing a halogenoalkane from alkane, what does the UV light cause?

Answer 5

Homolytic bond fission to produce halogen free radicals. [Note: Radicals are denoted by small dots.]

Question 6

How would you produce an alkene from a halogenoalkane?

Answer 6

Add hot ethanolic potassium hydroxide.

Question 7

From a halogenoalkane how would you produce a nitrile?

Answer 7

Add potassium cyanide in ethanolic solution under reflux.

Question 8

The production of nitriles from halogenoalkanes involves what mechanism?

Answer 8

Nucleophilic substitution. [Note: The cyanide ion acts as a nucleophile].

Question 9

What are the reagents and conditions needed to produce an amine from a nitrile?

Answer 9

Reagents: Hydrogen
Catalyst: Nickel
Conditions: 150 degrees centigrade and 5 atmospheres.
[Alternatively lithium aluminium hydride (ether) can be used.]

Question 10

Amines can be produced directly from halogenoalkanes using which reagents and conditions?

Answer 10

Reagent: Concentrated ammonia.
Conditions: Heat in a sealed tube.

Question 11

Halogenoalkanes can be produced from alkenes using hydrogen halides. What conditions are need for this?

Answer 11

Conditions: Room temperature

The hydrogen halide needs to be aqueous.

Question 12

What process is used to produce alkenes from alkanes?

Answer 12

Cracking.

Question 13

Alcohols can be can be produced from halogenoalkanes using what reagent?

Answer 13

Aqueous potassium hydroxide under reflux. [The hydroxide acts as a nucleophile and hydrogen halides are produced].

Question 14

What are the conditions and reagents needed to produce an alkene from an alcohol?

Answer 14

Add concentrated sulphuric acid under reflux.

Question 15

What are the conditions and reagents needed to produce an alcohol from an alkene?

Answer 15

Reagent: Steam
Catalyst: Concentrated phosphoric acid.
Conditions: 300 degrees centigrade and 60 atmospheres.

Question 16

What are the conditions and reagents needed to produce an ether from an alcohol?

Answer 16

Heat with sulphuric acid. [Can only be used with primary alcohols.]

Question 17

What are the conditions and reagents needed to produce an aldehyde from an alcohol?

Answer 17

Heat under distillation with acidified potassium dichromate. [Primary alcohols only]

Question 18

What are the conditions and reagents needed to produce a ketone from an alcohol?

Answer 18

Heat under reflux with acidified potassium dichromate. [Secondary alcohols only]

Question 19

What are the conditions and reagents needed to produce a carboxylic acid from an alcohol?

Answer 19

Heat under reflux with acidified potassium dichromate. [Primary alcohols only].

Question 20

What are the conditions and reagents needed to produce an alcohol from a carboxylic acid?

Answer 20

Add lithium aluminium hydride in dry ether.

Question 21

What are the conditions and reagents needed to produce an alcohol from a ketone?

Answer 21

Add lithium aluminium hydride in dry ether.

Question 22

What are the conditions and reagents needed to produce an alcohol from an aldehyde?

Answer 22

Add aqueous sodium borohydride and heat.

Question 23

What are the conditions and reagents needed to produce an alkyl hydrogensulphate from an alkene?

Answer 23

Add concentrated sulphuric acid.

Question 24

What are the conditions and reagents needed to produce an alcohol from an alkyl hydrogensulphate?

Answer 24

Add warm water.

Question 25

How can hydrogen bromide be produced?

Answer 25

By mixing 50% sulphuric acid with potassium bromide.

Question 26

Chloroalkanes can be prepared from alcohols using phosphorus (v) chloride. Other than the chloroalkane, what products are formed?

Answer 26

Phosphoryl chloride (POCl3) liquid and hydrogen chloride gas.

Question 27

Both phosphorus (III) bromide and phosphorus (v) bromide can be used to produce bromoalkanes from alcohols. Other than the bromoalkane, what products are formed when phosphorus (III) bromide is used?

Answer 27

H3PO3 liquid (Phosphorous acid).

Question 28

Hydrogen iodide cannot be used to produce iodoalkanes from alcohols. Why is this so?

Answer 28

Hydrogen iodide is unstable and is easily oxidised to iodine.

Question 29

Phosphorus (III) iodide can be used to produce iodoalkanes from alcohols but how must it be produced?

Answer 29

It must be produced in situe using a mixture of red phosphorus and iodine, as phosphorus (III) iodide it is unstable.

Question 30

Which of the following cannot be oxidised using acidified potassium dichromate:

a) propan-2-ol
b) ethanol
c) 2-methylpropan-2-ol
d) 3-methylbutan-2-ol

Answer 30

The answer is c.

Tertiary alcohols cannot be oxidised.

Question 31

Why is concentrated phosphoric acid preferred to concentrated sulphuric acid in the dehydration of alcohols?

Answer 31

Phosphoric acid produces a purer product.

Question 32

There are two ways of producing amines from halogenoalkanes. One produces a pure product and the other an impure product. Identify the synthesis of both.

Answer 32

1. Pure product from substitution using cyanide ions under reflux.
2. Impure product from substitution using ammonia as an impure product can form from further substitution.

Question 33

How can a diol be formed from an alkene and what would you observe in the reaction?

Answer 33

Add acidified potassium permanganate. The solution would go from pink to colourless.