Carbonyls, carboxylic acids, esters and other acyl groups

Question 1

What type of reaction and what is the product of the reaction of an aldehyde and Cr2O72-

Answer 1

oxidation. Carboxylic acid is produced

Question 2

Describe the mechanism for the reaction of a carbonyl and NaBH4

Answer 2

1. The lone pair of electrons from :H-(nucleophile), is attracted and donated to the + carbon in the C=O.
2. Dative covalent bond is formed between hydride ion and C=O.
3. The pi bond in C=O breaks by heterolytic fission forming negatively charged intermediate.
4. O of the intermediate donated lone pair to H in water. Intermediate has been protonated to form an alcohol.

Question 3

Describe the mechanism for the reaction of a carbonyl compound and NaCN/H+

Answer 3

1. Lone pair of electrons from -:CN is attracted and donated to + carbon in the C=O. Dative covalent bond forms.
2. The pi bond in C=O breaks by heterolytic fission forming negatively charged intermediate.
3. Intermediate is protonated by donating lone pair of electrons to H+ to form product.
4. Product is hydroxynitrile

Question 4

How does 2,4-dinitrophenylhydrazine detect presence of carbonyl group

Answer 4

NH2 group adds across the C=O and water is removed (condensation reaction) forming a yellow/orange precipitate

Question 5

How can you use 2,4-dinitrophenylhydrazine to identify the carbonyl.

Answer 5

The precipitate is filtered and solution left over is recrystallised. Bp is found and compared to known values of 2,4-DNP derivatives to find specific carbonyl.

Question 6

What will form when an aldehyde reacts with tollens reagent

Answer 6

carboxylic acid/silver mirror

Question 7

Why can’t tollens reagent react with a ketone

Answer 7

can not oxidize to form a carboxylic acid so no silver mirror formed

Question 8

Equation for the reaction of Ag in tollens reagent

Answer 8

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

Question 9

Are carboxylic acids soluble in water

Answer 9

Carboxylic acids with up to 4 carbon atoms are soluble in water because C=O and O-H bonds are polar so hydrogen bond is formed.

Question 10

Trend in solubility for carboxylic acids

Answer 10

as the number of carbon atoms increases, the solubility decreases as the non-polar carbon chain has a greater effect on the overall polarity of the molecule.

Question 11

Products of reaction between carboxylic acids and metals

Answer 11

hydrogen gas and carboxylate salt

Question 12

Observation for reaction between carboxylic acids and metals

Answer 12

metal disappears and effervescence

Question 13

Products of the reaction between carboxylic acids and metal oxides/alkalis

Answer 13

carboxylate salt (aq) and water

Question 14

Products of the reaction between carboxylic acids and carbonates

Answer 14

carboxylate salt, water and carbon dioxide. If carboxylic acid solid carbonate should disappear

Question 15

How can you distinguish carboxylic acids from other organic compounds

Answer 15

only organic compound that is sufficiently acidic enough to react with carbonates

Question 16

What is esterification

Answer 16

the reaction of an alcohol and a carboxylic acid to form an ester

Question 17

What are the products for the reaction between an alcohol and carboxylic acid

Answer 17

ester and water

Question 18

What are the conditions for esterification

Answer 18

concentrated sulfuric acid(catalyst) and heat

Question 19

Products of the reaction between acid anhydride and alcohol

Answer 19

ester and carboxylic acid

Question 20

Define hydrolysis

Answer 20

Chemical breakdown of a compound in the presence of water or in aqueous solution

Question 21

Conditions needed for acid hydrolysis

Answer 21

ester heated under reflux with dilute aqueous acid (catalyst). Ester broken down by water.

Question 22

State a difference between alkaline and acid hydrolysis

Answer 22

acid hydrolysis is a reversible reaction, alkaline hydrolysis is irreversible

Question 23

What are the products of acid hydrolysis

Answer 23

carboxylic acid and alcohol

Question 24

Conditions needed for alkaline hydrolysis

Answer 24

ester heated under reflux with aqueous hydroxide ions

Question 25

What are the products of alkaline hydrolysis

Answer 25

carboxylate ion and an alcohol

Question 26

Preparation of acyl chloride

Answer 26

carboxylic acid + SOCl2 (thionyl chloride) -> acyl chloride + SO2 + HCl

Question 27

Why are acyl chlorides useful in organic synthesis

Answer 27

very reactive. Easily converted into carboxylic acid derivatives with good yields. They react with nucleophiles by losing Cl- whilst retaining C=O.

Question 28

Why can acyl chloride react with phenol and carboxylic acids can’t

Answer 28

acyl chloride is more reactive

Question 29

Reaction of acyl chloride to form esters

Answer 29

acyl chloride + phenol/alcohol -> ester + HCl

Question 30

Products of the reaction between acyl chloride and water

Answer 30

carboxylic acid and HCl

Question 31

What is a primary amide

Answer 31

Nitrogen is attached to one carbon

Question 32

What is a secondary amide

Answer 32

Nitrogen attached to 2 carbons

Question 33

Products of reaction between acyl chloride and ammonia

Answer 33

primary amide and ammonium chloride

Question 34

Products of reaction between primary amine and acyl chloride

Answer 34

secondary amide and -chloride

Question 35

Acyl chloride functional group

Answer 35

O=C-Cl

Question 36

How to name an acyl chloride

Answer 36

Remove -oic acid from the carboxylic acid and add -oyl chloride

Question 37

Acid anhydride functional group

Answer 37

O=C-O-C=O

Question 38

Naming acid anhydrides

Answer 38

remove -acid from the carboxylic acid name and replace with anhydride

Question 39

Naming esters

Answer 39

From the carboxylic acid remove -oic acid and replace with -oate. For the alcohol remove the -anol and replace with -yl

Question 40

How to form tollen’s reagent?

Answer 40

Add AgNO3 to sodium hydroxide in a clean test tube until a brown precipitate forms (Ag2O). Add dilute ammonia until the precipitate dissolves to form a clear colourless solution.