Chapter 26 - Carbonyls and Carboxylic Acids

Question 1

What are carbonyl compunds ?

Answer 1

Compounds that contain a carbonyl functional group, C=O.

Question 2

Nomenclature for aldehydes?

Answer 2

Aldehydes have the suffix -al. As the C=O bond is always at the end of the carbon chain, there is no need for a number. A unbranched chain of 5 carbons, with an C=O bond at the end would be pentanal.

Question 3

Nomenclature for ketones?

Answer 3

The suffix is -one. For ketones with five or more carbons, you have to say which carbon the function group is on. For an unbranched 5 carbon chain, with the C=O bond on the second carbon, the name would be pentan-2-one.

Question 4

What do aldehydes oxidise to become?

Answer 4

Carboxylic acids

Question 5

Why are aldehydes easily oxidised?

Answer 5

There’s a hydrogen attached to the carbonyl group.

Question 6

What are the conditions to oxidise aldehydes?

Answer 6

You need to reflux them with acidified potassium dichromate.

Question 7

Why are ketones not easily oxidised?

Answer 7

You would have to break a carbon-carbon bond

Question 8

What does the reduction of an aldehyde form?

Answer 8

A primary alcohol.

Question 9

What does the reduction of a ketone form?

Answer 9

A secondary alcohol.

Question 10

What is the reducing agent used to turn ketones/aldehydes back into alcohols?

Answer 10

NaBH4- sodium tetrahybridoborate (III)

Question 11

What is the mechanism for the reduction of carbonyl compunds?

Answer 11

Nucleophillic addition

Question 12

How does Nucleophillic addition reactions work?

Answer 12

1) oxygen has negative dipole and carbon has positive dipole.

2) an arrow from the lone pair on the H- ion to the carbon atom. Then arrow from double bond to oxygen atom.

3) H atom now covalently bonded to carbon atom and oxygen has lone pair of electrons and a minus charge.

4) arrow from lone pair on oxygen to H atom on water molecules. Then from the bond to the oxygen atom in the water molecule. Make sure to draw dipoles on water molecules.

5) this forms an alcohol and a OH- ion.

Question 13

What does the reaction of carbonyl compounds with hydrogen cyanide produce?

Answer 13

Hydroxynitriles

Question 14

How does Nucleophillic addition work with hydrogen cyanide?

Answer 14

1) hydrogen cyanide dissociates in water to produce H+ ions and CN- ions.

2) arrow from CN- ion to carbon atom. Arrow from double bond to oxygen atom.

3) CN bonded to carbon and Oxygen Atom now has a lone pair of electrons. Arrow from lone pair to H+ ion

4) this forms a hydroxyl group and a hydroxynitrile is produced.

Question 15

What is used instead of hydrogen cyanide in labratories?

Answer 15

Sodium cyanide and Sulfuric acid.

Question 16

What reagent is used to identify is a carbonyl group is present?

Answer 16

Brady’s reagent - 2,4- dinitrophenylhydrazine

Question 17

What will you see if a carbonyl group is present when Brady’s reagent is added?

Answer 17

A bright orange precipitate forms. This only happens with ketones and aldehydes, not with COOH groups .

Question 18

How to identify the carbonyl compound from the orange precipitate formed from Brady’s reagent?

Answer 18

1) the precipitate is filtered and then recrystallised to form pure crystals.

2) then measure the melting point and compare to the literature values.

Question 19

How to distinguish between an aldehyde and a ketone?

Answer 19

Tollen’s reagent

Question 20

How does tollen’s reagent work + positive result?

Answer 20

Tollen’s reagent is a colourless solution of silver nitrate (AgNO3) dissolved in aqueous ammonia. It is heated in a test tube with an aldehyde. The aldehyde is oxidised to form a carboxylic acid. Then the silver ions in the Tollen’s reagent are reduced to produce a silver mirror.

Ag+ (aq). + e- ->. Ag(s)

Question 21

What are carboxylic acids?

Answer 21

Compounds with a -COOH functional group

Question 22

Why are carboxylic acids soluble?

Answer 22

Carboxylic acids are polar molecules, as there is a difference in electronegativity between the carbon and oxygen atoms. This allows carboxylic acids to form hydrogen bonds with water molecules.

Question 23

What is the dissociation of carboxylic acids?

Answer 23

As carboxylic acids are weak acids they dissociate into a carboxylate ion and H+. The H from the OH in the COOH is removed to form a H+ ion and a negative charge is left on the oxygen.

Question 24

Reaction of carboxylic acids and metals?

Answer 24

They react with metals to form a salt and hydrogen
Example : ethanoic acid + Mg -> magnesium ethanoate + H2

Question 25

Reaction of carboxylic acids with carbonates?

Answer 25

Carboxylic acids react with carbonates to form salt, carbon dioxide and water. Example: ethanoic acid + sodium carbonate -> sodium ethanoate + H20 + CO2

Question 26

Reaction of carboxylic acid and metal oxide?

Answer 26

This is a neutralisation reaction forming water and a salt. Example: ethanoic acid + magnesium oxide -> magnesium ethanoate + H2O

Question 27

What are acyl chlorides?

Answer 27

Acyl chlorides have the functional group COCl.

Question 28

General formula of acyl chlorides?

Answer 28

CnH2n-1OCl

Question 29

How to name acyl chlorides?

Answer 29

The names end with a -oyl chloride. So a five carbon chain with a COCl functional group at the end of the chain is called pentanoyl chloride.

Question 30

How to form acyl chlorides?

Answer 30

By reacting carboxylic acids with SOCl2 (thionyl chloride). This forms the acyl chloride, SO2 and HCl

Question 31

What is the reaction of acyl chloride with water?

Answer 31

Acyl chlorides react vigorously with cold water, producing a carboxylic acid. Example: ethanoyl chloride + H2O -> ethanoic acid + HCl

Question 32

Reaction of acyl chlorides with alcohols?

Answer 32

Acyl chlorides react vigorously with alcohols at room temperature, producing an ester and HCl. Example: ethanoyl chloride + Methanol -> methyl ethanoate + HCl

Question 33

Reaction of acyl chlorides with ammonia?

Answer 33

Acyl chlorides react violently with ammonia at room temperature, producing a primary amide. Example: ethanoyl chloride + NH3 -> ethanamide + HCl

Question 34

Reaction of acyl chlorides with amines?

Answer 34

Acyl chlorides react violently with amines at room temperature to form a secondary amide + HCl Example: ethanoyl chloride + methylamine -> N-methylethanamide + HCl

Question 35

Reaction of acyl chlorides with phenol?

Answer 35

Acyl chlorides react slowly with phenol at room temperature to form an ester +HCl. Example: ethanoyl chloride + phenol -> phenylethanoate + HCl

Question 36

What is an ester?

Answer 36

An ester is formed from a carboxylic acid and an alcohol group

Question 37

How do you name esters?

Answer 37

The first half of the name comes from the alcohol. The second part comes from the carboxylic acid group. So methanoic acid + ethanol would form ethyl methanoate.

Question 38

Reaction of ethanoic acid and ethanol + conditions?

Answer 38

Produces ethyl ethanoate + water. The reaction is called esterificstion and requires an acid catalyst usually concentrated H2SO4. The reaction is reversible

Question 39

What is an acid anhydride?

Answer 39

An acid anhydride is produced from two identical carboxylic acid molecules. The OH from one carboxylic acid is removed and the H from another is removed to form water.

Question 40

How do acid anhydrides produce esters?

Answer 40

They are heated with alcohols to form esters and a Carboxylic acid which can be seperated by distillation.

Question 41

How does acid hydrolysis of esters work?

Answer 41

This splits the ester into a carboxylic acid and an alcohol. You have to heat the ester under reflux with a dilute acid, such as hydrochloric or Sulfuric.

Question 42

How does base hydrolysis of esters work?

Answer 42

You reflux the ester with a dilute alkali such as sodium hydroxide. When heated, OH- ions from the base react with the ester and you get a carboxylate ion and an alcohol