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Chemistry Unit 4 > Carbonyl Compounds > Flashcards

Carbonyl Compounds Flashcards

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1
Q

What is a carbonyl group?

A

A carbon atom double bonded to an oxygen atom.

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2
Q

What is the test for aldehydes?

A

Tollen’s reagent (silver mirror, 5 minutes, water bath) or Fehling’s solution (brick red precipitate, water bath).

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3
Q

Give the equation for the reduction of Tollen’s reagent, and state what happens to the aldehyde.

A

Ag(NH3)2^+ + e- –> Ag +2NH3

This goes from colourless solution to silver precipitate. The aldehyde is oxidised to a carboxylic acid.

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4
Q

Give the equation for the reduction of Fehling’s solution, state what Fehling’s solution is and state what happens to the aldehyde.

A

Cu^(2+) + e- –> Cu^+
Copper(II) ions dissolved in NaOH.
This goes from a blue solution to a brick red precipitate.
The aldehyde is oxidised to a carboxylic acid.

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5
Q

What is Benedict’s solution?

A

The same as Fehling’s solution, but the copper(II) ions are dissolved in sodium carbonate instead.

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6
Q

Describe the method, product and risks of reacting carbonyls with hydrogen/potassium cyanide.

A

The HCN/KCN dissociates and the CN- ions attack the partially positively charged carbon atom of the C=O. The lone pair on the oxygen atom then grabs a H+ ion. This is nucleophilic addition and forms a hydroxynitrile. CN- ions are highly toxic.

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7
Q

What would you use as a reducing agent on an aldehyde or ketone?

A

H+ with a nickel catalyst/NaBH4 dissolved in water with methanol

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8
Q

Describe the mechanism for the reduction of an aldehyde.

A

A H- ion with a lone pair of electrons attacks the partially positively charges carbon of the C=O. The lone pair on the oxygen atom then grabs a H+ from water or a weak acid. This forms a primary alcohol.

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9
Q

Describe the mechanism for the reduction of a ketone.

A

A H- ion with a lone pair of electrons attacks the partially positively charges carbon of the C=O. The lone pair on the oxygen atom then grabs a H+ from water or a weak acid. This forms a secondary alcohol.

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10
Q

State the type of reaction that occurs when reducing an aldehyde or ketone.

A

Nucleophilic addition.

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11
Q

What is the functional group in a carboxylic acid?

A

-COOH

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12
Q

Where is the carboxyl group found?

A

At the end of a molecule.

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13
Q

Are carboxylic acids weak or strong?

A

Weak.

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14
Q

Describe the reaction of a carboxylic acid with a carbonate (CO3^(2-)).

A

carboxylic acid + carbonate –> salt + carbon dioxide + water

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15
Q

Name and decribe the reaction of a carboxylic acid with an alcohol.

A

This is called esterification. With heat, and in the presence of a strong acid catalyst (usually conc. H2SO4), you will produce an ester and water.

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16
Q

What is the functional group in an ester?

A

-COO-

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17
Q

What do esters smell like?

A

They smell sweet and usually fruity.

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18
Q

Name some common uses of esters.

A

Perfume, sweets, food, solvents (glue and printing ink) and plasticisers (make plastics more flexible).

19
Q

Why do esters make good solvents?

A

They are polar liquids, so will dissolve in most polar organic compounds. They have low boiling points, so evaporate easily.

20
Q

Vegetable oils and animal fats are esters of which alcohol?

A

Propan-1,2,3-triol.

21
Q

What is a fatty acid?

A

A long-chain carboxylic acid.

22
Q

Out of fats and oils, which are earier to melt and why?

A

Oils, because they contain unasaturated hydrocarbon chains. The double bonds in these chains mean they don’t pack together well, decreasing the effect of the van der Waals forces.

23
Q

What is hydrolysis?

A

When a substance is split up by water.

24
Q

When hydrolysing an ester, what can be used to speed up the process?

A

An acid or alkali.

25
Q

Describe acidic hydrolysis of an ester.

A

An equilibrium reaction of an ester with water to form a carboxylic acid and an alcohol. This reaction is the reverse of esterification and needs an acid catalyst (eg. HCl) and reflux.

26
Q

Describe basic hydrolysis of an ester.

A

This is an equilibrium reaction of an ester with OH- ions to form a carboxylate ion and an alcohol. This needs reflux conditions.

27
Q

Descrobe the hydrolisis of an oil or fat.

A

An oil or fat reacted with sodium hydroxide will produce glycerol (propan-1,2,3-triol) and a sodium salt.

28
Q

How do we form a fatty acid from a sodium salt?

A

Reacting it with HCl.

29
Q

What is biodiesel?

A

A mixture of methylesters of long chain carboxylic acids.

30
Q

How can we make biodiesel?

A

Reacting vegetable oils with methanol in the presence of a potassium hydroxide catalyst. This forms glycerol and biodiesel.

31
Q

Why isn’t biodiesel completely carbon neutral?

A

Because we use energy from fossil fuels to make the fertilizer that grows the crops to make biodiesel, and to plant, harvest and convert the oils.

32
Q

What is an acyl chloride?

A

A molecule with the functional group -COCl.

33
Q

What is an acid anhydride?

A

It is made from two identical carboxylic acids, that join across one oxygen molecule, ejecting water.

34
Q

Give the reaction for an acyl chloride with water.

A

acyl chloride + water –> carboxylic acid + HCl

35
Q

Give the reaction for an acyl chloride with an alcohol.

A

acyl chloride + alcohol –> ester + HCl

36
Q

Give the reaction for an acyl chloride with ammonia.

A

acyl chloride + ammonia –> amide + HCl

37
Q

Give the reaction for an acyl chloride with a primary amine.

A

acyl chloride + primary amine –> N-substituted amide + HCl

38
Q

Give the reaction of an acid anhydride with water.

A

acid anhydride + water –> 2 carboxylic acids

39
Q

Give the reaction for an acid anyhdride with an alcohol.

A

acid anhydride + alcohol –> ester + carboxylic acid

40
Q

Give the reaction for an acid anhydride with ammonia.

A

acid anhydride + ammonia –> amide + carboxylic acid

41
Q

Give the reaction for an acid anhydride with a primary amine.

A

acid anhydride + primary amine –> N-substituted amide + carboxylic acid

42
Q

Name and describe the mechanism of reactions involving acyl chlorides.

A

This is a nucleophilic addition elimination reaction. A nucleophile attacks the partially positively charged carbon atom of the C=O in the acyl chloride, and electrons from the double bond retreat to the oxygen atom. This leaves the nucleophile positively charged. The oxygen then reforms the double bond, and the C-Cl bond is broken. The chlorine is then a nucleophile, and attacks a hydrogen atom, forming HCl and allowing the positively charged nucleophile to gain electrons.

43
Q

Explain the industrial advantages of ethanoic anhydride over ethanoyl chloride in the manufacture of the drug aspirin.

A

It is cheaper, and it is safer - because it’s less corrosive, reacts more slowly with water, and doesn’t produce HCl gas when it reacts.

Chemistry Unit 4 (11 decks)

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