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Year 13 - Chemistry > C26 - Carbonyls and Carboxylic Acids > Flashcards

C26 - Carbonyls and Carboxylic Acids Flashcards

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1
Q

What happens when aldehydes are oxidised?

A

They form carboxylic acids (e.g. when refluxed with acidified dichromate ions).

Ketones will not undergo oxidation.

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2
Q

How does the reaction of carbonyl compounds differ to the type of reactions alkenes undergo?

A

Due to the polarity of the C=O bond in carbonyls, aldehydes and ketones can react with nucelophiles. Thus they can undergo nucleophilic addition.

Alkenes, with non polar C=C bonds, react with electrophiles via electrophilic addition.

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3
Q

What is NaBH4?

A

Sodium tetrahydridoborate.

It’s a reducing agent to reduce aldehydes and ketones to alcohols (under warm conditions).

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4
Q

What’s sodium tetrahydridoborate?

A

NaBH4

It’s a reducing agent to reduce aldehydes and ketones to alcohols (under warm conditions).

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5
Q

What happens when aldehydes and ketones are reduced?

A

Under warm conditions, using reducing agent NaBH4, aldehydes are reduced to primary alcohols and ketones are reduced to secondary alcohols.

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6
Q

How do carbonyls react with HCN, hydrogen cyanide?

A

HCN is extremely poisonous and has a low boiling point so it must be carried out in a fume cupboard.

It also can’t be used directly (due to being poisonous) so sodium cyanide and sulphuric acid are used to produce the HCN.

It can result in the length of the carbon chain increasing.

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7
Q

What happens when carbonyls react with HCN, hydrogen cyanide?

A

The H and C≡N bond across the C=O.

HCN is extremely poisonous and has a low boiling point so it must be carried out in a fume cupboard.

It also can’t be used directly so sodium cyanide and sulphuric acid are used to produce the HCN.

It can result in the length of the carbon chain increasing.

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8
Q

What is used to produce HCN, hydrogen cyanide, in reactions with carbonyls?

(Conditions)

A

Sodium cyanide and sulphuric acid.

The reaction is carried out in a fume cupboard.

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9
Q

What is produced when hydrogen cyanide reacts specifically with aldehydes?

A

Hydroxynitriles (or cyanohydrins)

They contain hydroxyl and nitrile functional groups.

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10
Q

What happens in the mechanism for the reaction with NaBH4?

A

Nucleophilic addition

1) The lone pair of electrons from the hydride ion ( :H- ) is attracted and donated to the (+) carbon atom in the carbonyl C=O double bond.
2) A dative covalent bond is formed between the hydride ion and carbon atom.
3) The pi bond in the C=O bond breaks by heterolytic fission, forming a negatively charged intermediate.

4) The oxygen atom of the intermediate donates a lone pair of electrons to a hydrogen atom in a water molecule.
The intermediate becomes pronated into an alcohol.

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11
Q

What acts as the nucleophile in the reaction of NaBH4 with carbonyls?

A

A hydride ion

:H -

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12
Q

What happens in the mechanism for the reaction with HCN?

A

Nucleophilic addition

1) The lone pair of electrons from the cyanide ion ( :CN- ) is attracted and donated to the (+) carbon atom in the carbonyl C=O double bond.
2) A dative covalent bond is formed between the hydride ion and carbon atom.
3) The pi bond in the C=O bond breaks by heterolytic fission, forming a negatively charged intermediate.

4) The oxygen atom of the intermediate donates a lone pair of electrons to a hydrogen atom in a water molecule.
The intermediate becomes pronated into a hydroxynitrile.

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13
Q

What acts as the nucleophile in the reaction of hydrogen cyanide with carbonyls?

A

A cyanide ion

:C≡N -

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14
Q

What is Brady’s reagent?

A

(A.k.a 2,4-dinitrophenylhydrazine OR 2,4-DNP)

It’s used to detect the presence of the carbonyl functional group. (Detects both aldehydes and ketones).

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15
Q

What is 2,4-dinitrophenylhydrazine / 2,4-DNP?

A

Brady’s reagent

It’s used to detect the presence of the carbonyl functional group. (Detects both aldehydes and ketones).

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16
Q

How is 2,4-DNP / Brady’s reagent used?

A

When added to the unknown compound, if produces a yellow/orange precipitate, a carbonyl is present.

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17
Q

What is used to distinguish between aldehydes and ketones?

A

Tollens’ reagent

It will oxidise an aldehyde into a carboxylic acid and form a silver mirror (as silver ions get reduced).
Ketones won’t react as they won’t further oxidise.

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18
Q

What happens when Tollens’ reagent is added to carbonyls?

A

It contains silver ions which act as an oxidising agent (in the presence of ammonia).

It will oxidise an aldehyde into a carboxylic acid and form a silver mirror (as silver ions get reduced).
Ag+ + e- -> Ag

Ketones won’t react as they won’t further oxidise.

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19
Q

How soluble are carboxylic acids?

A

The C=O and O-H bonds are polar, allowing them to form hydrogen bonds with water molecules.

As the number of carbon atoms increases, solubility decreases as the non-polar carbon chain has a greater effect on the overall polarity of the molecule.
(Carboxylic acids with up to 4 C atoms are soluble in water)

20
Q

How acidic are carboxylic acids?

A

They’re classified as weak acids.

More acidic than phenols and alcohols

21
Q

How do carboxylic acids react with metals and bases?

A

They undergo redox reactions with metals and neutralisation reactions with bases.

This forms carboxylate salts.

22
Q

What is the test for carboxyl groups?

A

React with carbonates.

Carboxylic acids are the only common organic compound acidic enough to react with carbonates. (E.g. phenols not acidic enough to react with carbonates)

23
Q

What are the (4) carboxylic derivatives?

A

Esters

Acyl chlorides

Acid anhydrides

Amides

24
Q

What are esters?

A

A carboxylic derivative.

To name an ester, the -oic acid suffix is replaced with -oate.

-COO-

25
Q

What are acyl chlorides?

A

Carboxylic derivatives, named by replaced the -oic acid suffix with -oyl chloride.

-COCl

26
Q

What are acid anhydrides?

A

Carboxylic derivatives formed by the removal of water from 2 carboxylic acid molecules.

They’re named by replacing ‘acid’ with ‘anhydride’.

27
Q

What is esterification?

A

A condensation reaction of an alcohol with a carboxylic acid to form an ester (and water).

This is done under warm conditions in the presence of concentrated sulphuric acid.

28
Q

What are the conditions for the esterification/condensation reaction of an alcohol and carboxylic acid?

A

Warm conditions and concentrated sulfuric acid catalyst.

29
Q

What are the two types of hydrolysis of esters?

A

Acid hydrolysis (produces alcohol and carboxylic acid)

Alkaline hydrolysis (produces an alcohol and carboxylate salt which requires additional acid to form a carboxylic acid)

30
Q

What conditions are needed for the acid hydrolysis of an ester?

A

Reflux with dilute aqueous acid

The ester is broken down by water with the acid acting as a catalyst.

(Acid hydrolysis produces alcohol and carboxylic acid).

31
Q

What conditions are needed for the alkaline hydrolysis of an ester?

A

Reflux with aqueous hydroxide ions.

Alkaline hydrolysis produces an alcohol and carboxylate salt which requires additional acid to form a carboxylic acid

32
Q

What conditions are needed for the preparation of acyl chlorides?

A

They can be prepared directly by reacting their parent carboxylic acid with thionyl chloride, SOCl₂.

This should be carried out in a fume cupboard as SO₂ and HCl are also produced.

33
Q

How are acyl chlorides produced?

A

A carboxylic acid is reacted with thionyl chloride, SOCl₂.

This should be carried out in a fume cupboard as SO₂ and HCl are also produced.

E.g. propanoic acid becomes propanoyl chloride.

34
Q

How do acyl chlorides react with other organic compounds?

A

They’re very reactive and react with nucleophiles by losing the Cl- ion whilst retaining the C=O bond.

(Can react with alcohols, phenols, water, ammonia and amines)

35
Q

What is formed in the reaction between a carboxylic acid and alcohol?

A

An ester and water

36
Q

What is formed in the reaction between a carboxylic acid and thionyl chloride?

A

An acyl chloride, HCl and SO₂

Thionyl chloride is SOCl₂

37
Q

What is formed in the reaction between a carboxylic acid and carboxylic acid?

A

An acid anhydride and water

38
Q

What is formed in the reaction between an acid anhydride and alcohol?

A

An ester and carboxylic acid

39
Q

What is formed in the reaction between an acyl chloride and alcohol?

A

An ester and HCl

40
Q

What is formed in the reaction between an acyl chloride and phenol?

A

A phenylester and HCl

41
Q

What is formed in the reaction between an acyl chloride and water?

A

A carboxylic acid and HCl

Very vigorous reaction forming steamy HCl fumes

42
Q

What is formed in the reaction between an acyl chloride and (2) ammonia?

A

An amide and NH₄Cl

43
Q

What is formed in the reaction between an acyl chloride and amine?

A

An N-substituted amide and alkylammonium chloride

44
Q

What is the functional group of an acyl chloride?

A

-COCl

45
Q

What is the functional group of an amine?

A

-NH₂

46
Q

What is the functional group of an amide?

A

-CONH₂ / -CONR

47
Q

What is the functional group of an acid anhydride?

A

(RC(O))₂O

E.g. (CH3CO)₂O

Year 13 - Chemistry (12 decks)

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