C26 - Carbonyls and Carboxylic acids

Question 1

What is the carbonyl functional group and what compounds is it seen in?

Answer 1

C=O

Ketones, aldehydes and carboxylic acids

Question 2

What reactants can be used in place of HCN, why would this be useful?

Answer 2

H2SO4 and NaCN (provides HCN in situ)

HCN is poisonous and gas slightly above room temperature (so difficult and dangerous to use)

Question 3

Why is the reaction of carbonyls with HCN useful?

Answer 3

Increases length of the carbon chain

Question 4

What reagent is used to detect C=O bonds (2 names) and what does a positive test look like?

Answer 4

2,4-DNP or Brady’s reagent

yellow or orange ppt formed

Question 5

How can you distinguish between aldehydes and ketones?

Answer 5

Tollen’s reagent (silver nitrate and aq ammonia) acts as oxidising agent
Silver mirror formed (for aldehydes)
No reaction for ketones

Question 6

After reacting a carbonyl with Brady’s reagent, how could you check whether it was a ketone or aldehyde?

Answer 6

Recystralise and purify ppt
Measure melting point
Compare to known values

Question 7

What is the strength of carboxylic acids?

Answer 7

Weak acids

Partially dissociate in water

Question 8

Carboxylic acid + metal –>

Answer 8

carboxylate salt + hydrogen

Question 9

Carboxylic acid + metal oxide–>

Answer 9

carboxylate salt + water

Question 10

Carboxylic acid + alkali–>

Answer 10

carboxylate salt + water

Question 11

Carboxylic acid + carbonate –>

Answer 11

carboxylate salt + water + carbon dioxide

Question 12

For an ester written in structural formula, which reactant is shown first?

Answer 12

Carboxylic acid section then alcohol section

Question 13

For an ester, which order is the IUPAC name written?

Answer 13

alcohol (eg. methyl)
carboxylic acid (eg. methanoate)

Question 14

When forming an ester, the side product is water. Where do each of the atoms come from?

Answer 14

OH from alcohol

H from carboxylic acid

Question 15

What is an acyl chloride?

Answer 15

Carboxylic acid but with Cl in place of OH
R-C=O
|
Cl

Question 16

Why are acyl chlorides used in place of carboxylic acids?

Answer 16

Cl is a better leaving group than OH
Forming an ester with a carboxylic acid, the reaction is reversible, conditions = under reflux with H2SO4 catalyst. With acyl chloride, rtp no catalyst

Question 17

How do you form an acyl chloride?

Answer 17

Carboxylic acid + SOCl2 –> acyl chloride + SO2 +HCl

Question 18

Equation for hydrolysis of an ester in acid conditions

Answer 18

ester + H2O –(h+)–> carboxylic acid + alcohol

Question 19

Equation for hydrolysis of an ester in acid conditions. Name of type of reaction.

Answer 19

ester + OH- –> carboxylate ion + alcohol

Saponification

Question 20

What is an acid anhydride?

Answer 20

2 carboxylic acids that have reacted together (and released water)