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Chemistry 4 > Reactions of organic compounds > Flashcards

Reactions of organic compounds Flashcards

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1
Q

What is an addition reaction?

A

Involves the breaking of the C=C double bond, allowing another molecule to combine to form the larger one.

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2
Q

Give a description of an addition reaction?

A
  • involves an unsaturated compound

- one product is formed

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3
Q

Under what conditions does an addition reaction occur?

A

For alkenes:

- UV light

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4
Q

What is hydrogenation?

Under what conditions does this reaction occur?

A 
The addition of hydrogen to an unsaturated compound
Forms saturated compound (alkane) 
Requires:
- metal catalyst: Ni
- 600˚c
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5
Q

What is a hydration reaction?

Under what conditions does this reaction occur?

A 
Addition of water to an unsaturated 
Requires:
- HPO3 
- catalyst
- 300˚c
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6
Q

What is halogenation? (4)

A
  • Addition of a halogen to an unsaturated compound
  • Forms a haloalkane
  • Allows product to undergo more reactions due to the presence of more electronegative atom, thus compound is more unstable
  • Allows for alcohols and amines to be produced
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7
Q

How can an amine be produced?

A

Chloroalkane + concentrated ammonia

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8
Q

What is addition polymerisation?

A

Small unsaturated monomers are joined together to form a polymer.

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9
Q

What is a substitution reaction?

A

Replacement of an atom or group of atoms by another.

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10
Q

Give a description of a substitution reaction.

A
  • usually involves saturated molecule
  • two new products are formed
  • if reactant is concentrated, further reactions could occur, resulting in all hydrogens replaced with Cl
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11
Q

Under what conditions does a substitution reaction occur?

A

Requires:

  • UV light
  • heat
  • catalyst (since reaction is slow)
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12
Q

How would you separate molecules which have undergone substitution from those which have not undergone substitution?

A

The different substituted products have different boiling points so they may be separated from one another by fractional distillation.

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13
Q

How can an alcohol be produced from a haloalkane?

A
  • Because of the large electronegativity difference between Cl and C, there will be a polar bond
  • As a consequence of the highly polarised bond, the partial positive charge on the C atom can be attacked by a negatively charged species such as a hydroxide ion
  • RCl ——-> ROH + HCl
    OH-
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14
Q

What is the oxidation reaction of alcohols?

A

Involves a change in oxidation numbers as the alcohol is oxidised to form

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15
Q

Write the equation for the reaction between a chloroalkane and a water molecule.

A

Chloroethane + H2O ————> Ethanol + HCl
Catalyst
Requires a catalyst to speed up the reaction.

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16
Q

What are the three oxidation reactions of alcohols?

A
  1. primary alcohol →aldehyde →carboxylic acid;
  2. secondary alcohol→ketone →no further oxidation;
  3. tertiary alcohol →not oxidised.
17
Q

How is an ester formed?

A

Via an esterfication reaction (condensation).
An alcohol and carboxylic acid are combined.
The products are an ester and a molecule of water.

18
Q

Under what conditions does an esterification reaction occur?

A
  • heat
  • concentrated liquid H2SO4
  • all states are liquid
19
Q

What is the hydrolysis reaction of an ester?

A

Esters can react with water to form a carboxylic acid and an alcohol

20
Q

Under what conditions can an ester undergo hydrolysis?

A
  • heat
  • catalyst
  • water
21
Q

What happens when an ester is hydrolyzed by an alkali metal? eg NaOH?

A

The products are an alcohol and the sodium salt of the carboxylic acid.
The sodium salt can be easily converted to the carboxylic acid by adding a dilute acid solution, such as hydrochloric acid.

22
Q

How can a sodium salt of a carboxylic acid be converted into just a carboxylic acid?

A

The sodium salt can be easily converted to the carboxylic acid by adding a dilute acid solution, such as hydrochloric acid.
This regenerates the protonated carboxylic acid.

23
Q

What reactions can carboxylic acids undergo?

A
  • esterification
  • react with bases: neutralization
  • ionize in water
  • react with ammonia: form amide
24
Q

How can a carboxylic acid be converted into an amide?

A

Carboxylic acids react with ammonia.
Products will be a primary amide and a molecule of water.
Condensation reaction.

25
Q

How can a secondary amide be formed from a carboxylic acid?

A

Formed when carboxylic acids react with primary amines. An amide link is formed in this reaction.

26
Q

What happens when a primary alcohol is oxidized?

What must the conditions be for the first and second stage?

A

First oxidized to form aldehydes and then further oxidation forms the corresponding carboxylic acids.

  1. H+ / Cr2O7 2-
  2. H+ / Cr2O7 2- and heat
27
Q

How can a primary alcohol be oxidised to only an aldehyde?

not a carboxylic acid

A

Milder conditions: lower temperatures and shorter reaction time
The aldehyde can be distilled from the reaction mixture as it is formed so that it is not
oxidised further.
Higher temperatures and longer reaction times favour the formation of the carboxylic acid over the aldehyde.

28
Q

What happens when a secondary alcohol is oxidized?

What must the conditions be for the first and second stage?

A

A ketone will be produced.
1. strong oxidising agents
H+ / Cr2O7 2- or H+ / MnO4 -

29
Q

What colour changes can occur in an oxidation reaction of an alcohol?
Orange to ?
Purple to ?

A

Strong oxidants are coloured due to the presence of transition metals.
When orange dichromate is used to oxidise an alcohol, the dichromate is reduced, which is green in colour.
When deep purple acidified potassium permanganate oxidises alcohols, the manganese is reduced, which is colourless.
Tertiary alcohols will not undergo a colour change.

30
Q

Why can a tertiary alcohol not undergo oxidation?

A

Tertiary alcohols are resistant to reaction with solutions of strong oxidants.
The carbon attached to the hydroxyl group does not have a C–H bond to break, so oxidation cannot occur at that carbon atom.

31
Q

What is the condensation reaction between an amine and a carboxylic acid?

A

Will form a secondary amide.

The hydrogen of the primary amine is lost and combines with the –OH from the carboxylic acid

32
Q

What is a reaction pathway to synthesise a haloalkane? (2)

A
  • alkane → substitution with HCl

- alkene → addition with HCl

33
Q

What is a reaction pathway to synthesise a primary alcohol? (2)

A
  • alkene addition with Cl → chloroalkane with NaOH → primary alcohol
  • alkene addition with H2O → primary alcohol
34
Q

What is a reaction pathway to synthesise a carboxylic acid?

A

alkane substitute with Cl → chloroalkane sub with OH- → primary alcohol oxidise with oxidant → carboxylic acid

35
Q

Why is the substitution reaction of propane a better choice than an addition reaction of propene in the reaction pathway for a carboxylic acid?

A

This is because the addition of HCl to propene results in the formation of unwanted 2-chloropropane.

36
Q

What is a reaction pathway to synthesise an ester?

A

primary alcohol with carboxylic acid and H2SO4 → ester

37
Q

How can you separate the desired product from a mixture of reactants?

A

Can be separated from the reaction mixture and purified by fractional distillation due to the differences in boiling points.

38
Q

What are the considerations when devising a reaction pathway t o synthesise a compound? (2)

A
  • the equilibrium position of a reaction can have a considerable impact on the overall yield.
  • the principles of ‘green’ chemistry must also be considered in terms of the solvents required and the by-products that are formed.

Chemistry 4 (7 decks)

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