Carbonyls and carboxylic acid derivatives

Question 1

what is the mechanism for the Nucleophilic Addition of Carbonyls with NaBH4/HCN?

Answer 1

Nucleophilic attack of NaBH4/HCN on the carbonyl carbon followed by protonation (for HCN) or hydride transfer (for NaBH4).

Question 2

Use of 2,4-Dinitrophenylhydrazine (DNPH)?

Answer 2

-DNPH reacts with Aldehyde/Ketone compounds to form yellow to orange precipitates.
- Melting point analysis of the DNPH derivative can identify the specific carbonyl compound.

Question 3

Use of Tollens (Ammoniacal Silver Nitrate)?

Answer 3

-Detecting the Presence of an Aldehyde: Tollens’ reagent reacts with aldehydes but not with ketones to form a silver mirror.

Question 4

Why are carboxylic acids soluble in water?

Answer 4

A hydrogen bond forms between the delta minus oxygen of the double bond and the delta positive hydrogen of the water making it soluble in water.

Carboxylic acids with up to 4 carbons are water soluble, longer chains are less soluble.

Question 5

Are carboxylic acids weak or strong?

Answer 5

Weak as they only partially ionise in water to form H+ ions

Question 6

What forms in reactions between carboxylic acids and metal acids/alkalis?

Answer 6

Carboxylate salt and water

Question 7

What forms in reactions between carboxylic acids and metals?

Answer 7

Carboxylate salt and H2

Question 8

What forms in reactions between carboxylic acids and carbonates?

Answer 8

Co2, Water and a carboxylate salt.

if carboxylic acid is in excess a solid carbonate would disappear

Question 9

How to test for a carboxylic acid?

Answer 9

Add carbonates as carboxylic acids are the only organic compound acidic enough to react with them to effervesce

Phenols wont react so differentiates them from them

Question 10

What is an acid anhydride?

Answer 10

Compound formed from 2 carboxylic acids reacting, releasing water.

Removes the -OH group from both and binds at this point to form an ester bond with an =O on each adjacent carbon.

Question 11

How to name acyl chlorides?

Answer 11

Take the parent carboxylic acid name, remove the ‘-oic acid’ and add ‘-oyl chloride’

Question 12

Describe acid hydrolysis of an ester?

Answer 12

Heat the ester under reflux with a dilute aqueous acid, the ester is broken down by the water with the acid acting as a catalyst to form a carboxylic acid and an alcohol.

Question 13

Describe alkaline hydrolysis of an ester

Answer 13

Forms a carboxylate salt and an alcohol

Irreversible

Heat under reflux with aqueous hydroxide ions

Question 14

How to make acyl chlorides?

Answer 14

React the parent carboxylic acid with thionyl chloride (SOCl2).

Forms the acyl chloride, SO2 and HCL

Done in a fume cupboard as the products are toxic

Question 15

Reaction uses of acyl chlorides

Answer 15

Very reactive

Easily converted into carboxylic acid derivatives, eg esters/amides, with good yields

React with nucleophiles by losing the chloride ion while retaining the C=O bond

Question 16

Acyl chloride + nucleophile mechanism

Answer 16

• Nucleophile attacks partially positive carbon of carbonyl group, breaking c=o bond
• Leaves a tetrahedral intermediate with a negatively charged oxygen atom
• The leaving group, normally a chloride ion, departs, stabilising the intermediate
• The tetrahedral intermediate rearranges to reform the carbonyl group, forming an acyl compound bonded to the nucleophile