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A2 Chemistry Unit 1 > Carbonyls, Esters and Carboxylic Acids > Flashcards

Carbonyls, Esters and Carboxylic Acids Flashcards

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0
Q

How are ketones prepared? And example.

A

The oxidation of secondary alcohols using acidified potassium dichromate.

Butan-2-one is prepared from butan-2-ol

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1
Q

How are aldehydes prepared? And example

A

The oxidation of primary alcohols using acidified potassium dichromate. The oxidation has to be carefully controlled so the aldehyde isn’t further oxidised to a carboxylic acid.

Eg. CH3CH2CH2CH2OH + [O] -> CH3CH2CH2CHO

Butan-1-ol to butanal

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2
Q

What are aldehydes reduced to?

A

Primary alcohols

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3
Q

What are ketones reduced to?

A

Secondary alcohols

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4
Q

How can the presence of an aldehyde or ketone carbonyl group be identified?

A

Using a solution of Brady’s reagent (2,4-DNP)

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5
Q

How can you distinguish between aldehydes and ketones?

A

Using Tollens’ reagent and acidified potassium dichromate after they are reacted with 2,4-DNP

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6
Q

What is the result when ketones or aldehydes are reacted with 2,4-DNP?

A

They give an orange crystalline precipitate called a 2,4-dinitriphenylhydrazone.

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7
Q

Distinguishing test 1:

Do either aldehydes or ketones react with Tollens’ reagent? What happens when it reacts?

A

Aldehydes react with Tollens’ reagent; they are oxidised to a carboxylic acid and a silver mirror is formed.

No reaction with ketones.

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8
Q

Distinguishing test 2:

How do aldehydes and ketones react with acidified potassium dichromate?

A

Aldehydes are oxidised to carboxylic acids and the potassium dichromate turns from orange to green.

No reaction with ketones and therefore the dichromate stays orange in colour.

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9
Q

What do aldehydes and ketones react with in a nucleophilic addition reaction?

A

NaBH4. The BH4- ion acts as a source of hydride ions.

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10
Q

What is the nucleophile in the nucleophilic addition reaction of aldehydes and ketones?

A

Hydride ion acts as a nucleophile

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11
Q

Describe the nucleophilic addition reaction of aldehydes and ketones with NaBH4

A
  1. The electron deficient carbon atom in the polar C=O double bond is attacked by the hydride ion, which acts as a nucleophile.
  2. The lone pair of electrons from the hydride ion forms a bond with the carbon atom.
  3. At the same time, the pi bond in the C=O bond breaks to produce a negatively charged intermediate.
  4. The intermediate donates an electron pair to a hydrogen atom of an H2O molecule, forming a dative covalent bond and a hydroxide ion, OH-
  5. The organic product is an alcohol.
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12
Q

What reducing agent is used to reduce carbonyl compounds to alcohols?

A

NaBH4 (sodium tetrahydridoborate(III))

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13
Q

What is put in brackets in the equation to show a reactant is being reduced?

(Like [O] when it’s being oxidised)

A

Hydrogen. [H]

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14
Q

How is it possible to positively identify the carbonyl compound after you’ve identified it as an aldehyde or ketone?

A

Carrying out further experiments on the 2,4-DNP derivative

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15
Q

How do you carry out further experiments on the 2,4-DNP derivative to identify the compound?

A
  1. The yellow/orange solid, 2,4-DNP derivative is slightly impure.
  2. The impure product is filtered and recrystallised to produce a purified sample of yellow or orange crystals. This is filtered and dries.
  3. The melting point is measured and recorded.
  4. The melting point is then compared to a database or data table to identify the original aldehyde or ketone.
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16
Q

Are carboxylic acids soluble in water?

A

Yes. The highly polar C=O and O-H bonds allow carboxylic molecules to form hydrogen bonds with water molecules.

17
Q

Does the solubility of carboxylic acids increase or decrease as the carbon chain gets longer? Why?

A

As the number of carbon atoms in the carboxylic acid acids increases, the solubility decreases.

This is the result of the longer non-polar hydrocarbon chain in the molecule that does not interact with water molecules.

18
Q

Carboxylic acids are weak acids compared to…

A

Nitric, sulfuric and hydrochloride acids

19
Q

what are salts formed from carboxylic acids known as?

A

Carboxylates.

20
Q

What is he name of the salt formed from methanoic acid?

A

Methanoate.

21
Q

How do carboxylic acids react with metals?

A

Forms a salt and hydrogen gas-there will be effervescence during the reaction.

22
Q

What is the equation for the reaction between ethanoic acid and sodium metal?

A

CH3COOH + Na -> CH3COO-Na+ + 1/2H2

Ethanoic acid + sodium metal -> sodium ethanoate and hydrogen gas

23
Q

How do carboxylic acids react with bases?

A

They form a salt and water.

24
Q

What is the equation for the reaction between propanoic acid and aqueous potassium hydroxide?

A

CH3CH2COOH + KOH -> CH3CH2COO-K+ + H2O

Propanoic acid + aqueous potassium hydroxide -> potassium propanoate + water

25
Q

How do carboxylic acids react with carbonates?

A

Forms a salt, carbon dioxide and water

26
Q

What is the equation for the reaction between methanoic acid and sodium carbonate?

A

2HCOOH + Na2CO3 -> 2HCOO-Na+ + CO2 + H2O

Methanoic acid + sodium carbonate -> sodium methanoate + carbon dioxide + water

27
Q

What is esterification?

A

The reaction of an alcohol with a carboxylic acid to produce an ester and water.

28
Q

How do we make esters from carboxylic acids?

A

Through esterification.
Carboxylic acid + alcohol water + ester
-concentrated sulfuric acid is used as a catalyst

29
Q

How do we make esters from acid anhydrides?

A

Acid anhydride is gently heated with an alcohol.

30
Q

Why is preparing esters from acid anhydrides better than preparing them from carboxylic acids?

A

Preparing esters from acid anhydrides gives a much better yield of the ester.

31
Q

What happens in acid hydrolysis of esters?

A
  1. the ester is heated under reflux with dilute sulfuric acid or dilute hydrochloride acid.
  2. Ester is broken down by water, with the acid acting as a catalyst.
32
Q

What happens in alkaline hydrolysis of esters?

A

Aqueous sodium hydroxide is refluxed with the ester.

This reaction is non-reversible and leads to the formation of the sodium salt of the carboxylic acid.

33
Q

Equation for the acid hydrolysis of propyl ethanoate

A

CH3COOCH2CH2CH3 + H2O -> CH3COOH + HO-CH2CH2CH3

Propyl ethanoate + water -> ethanoic acid + propan-1-ol

34
Q

What is the alkaline hydrolysis of esters sometimes called? Why?

A

Saponification.

Because it’s the basis of soap-making.

35
Q

What are esters used in?

A

-Perfumes and flavourings.
Many natural perfumes like oil of wintergreen and the scents of flowers are esters.
-as solvents: used for dissolving substances like drugs and antibiotics
-in biodiesel

36
Q

What are fats?

A

Esters of long-chain carboxylic acids (fatty acids) and the alcohol glycerol.

37
Q

What are triglycerides?

A

A triester of glycerol and fatty acids.

38
Q

What are fatty acids?

A

Long-chain carboxylic acids

39
Q

Why are trans fatty acids bad for our health?

A

Causes an increase in LDLs which can lead to increased risk of coronary heart disease and strokes.

40
Q

Why are esters of fatty acids being used as biodiesel?

A

They are renewable
Easily produced using waste cooking oil
Natural sources occur as well
(rapeseed in the UK)

41
Q

How are fatty acids used as biodiesel?

A

Biodiesel is an ethyl or methyl ester of a fatty acid
Made by transesterification
-triglycerides reacted with methanol or ethanol in presence of KOH or NaOH catalyst
Glycerol is also formed and is used for pharmaceuticals or cosmetics -> improves atom economy

A2 Chemistry Unit 1 (8 decks)

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