MODULE 6: Carbonyls and Carboxylic Acids

Question 1

What is an aldehyde group?

Answer 1

H-C=O

Question 2

What is a ketone group?

Answer 2

R-C(=O)-R

Question 3

How are carbonyls oxidised?

Answer 3

Acidified potassium dichromate under reflux

Question 4

What is the features of the C=O bond?

Answer 4

Reactive due to polarity

Question 5

What is the difference between the species that attack C=C and C=O?

Answer 5

Electrophilic addition = C=C

Nucleophilic addition = C=O

Question 6

How are carbonyls reduced?

Answer 6

Using NaBH4, which reduces them into alcohols

Question 7

How does cyanide react with carbonyls?

Answer 7

With sulfuric acid to form a hydroxynitrile

Question 8

What tests are there for carbonyl tests?

Answer 8

• 2,4-DNP (brady’s reagent), forms an orange precipitate when a carbonyl group is present.
• Tollens reagent, silver nitrate and ammonia. If an aldehyde is present, a silver mirror is formed.
• With the precipitate formed from DNP, test boiling/melting point and compare to known values

Question 9

Why are carboxylic acids more water soluble than carbonyls?

Answer 9

More opportunities to hydrogen bond with water

Question 10

Why are carboxylic acids weak acids?

Answer 10

Because they only partially dissociate the hydrogen ions

Question 11

What reactions do carboxylic acids undergo?

Answer 11

Redox reactions with metals and neutralisation reactions with bases

Question 12

What are the products of reactions with carboxylic acids and metals?

Answer 12

Carboxylate salt (RCOO-X+) and hydrogen gas

Question 13

What are the products of carboxylic acids in neutralisation reactions?

Answer 13

• Metal oxides: carboxylate salt (RCOO-X+) and water
• Alkalis: carboxylate salt (RCOO-X+) and water
• Carbonates: carboxylate salt (RCOO-X+), carbon dioxide and water

Question 14

What are the main derivatives of a carboxylic acid?

Answer 14

Esters, acid anhydrides, acyl chlorides, amides

Question 15

What are esters?

Answer 15

A hydrocarbon that has a double bonded oxygen to a carbon, and then another oxygen single bond linking two carbons together

Question 16

What are acyl chlorides?

Answer 16

Similar to esters, except with a double bonded oxygen and a chloride group attached. PropanOYL CHLORIDE

Question 17

What are acid anhydrides?

Answer 17

Two carboxylic acids that have bonded to form a double bonded oxygen on each carbon around a single bonded oxygen

Question 18

What is esterification?

Answer 18

A method of making esters using alcohols and carboxylic acids. Concentrated sulfuric acid acts as a catalyst and the solution is added to 80oc water bath to allow the reaction. It is a condensation reaction, so forms a mole of water.

Question 19

What are some physical properties of esters?

Answer 19

Sweet/fruity smells and tastes

Question 20

What are the two types of hydrolysis for esters?

Answer 20

Acid and alkaline

Question 21

What is acid hydrolysis for esters?

Answer 21

Reverse esterification, reversible reaction. Ester heated under reflux with dilute acid.

Question 22

What is alkaline hydrolysis for esters?

Answer 22

Also known as saponification; irreversible. Ester is heated under reflux with OH- to form a carboxylate ion and an alcohol.

Question 23

How are acyl chlorides prepared?

Answer 23

Carboxylic acid with thionyl chloride (SOCl2) to form an acyl chloride, SO2 and HCl gas.

Question 24

Why are acyl chlorides useful in organic synthesis?

Answer 24

Can be converted into other carboxylic derivatives with a good yield, as well as being much more reactive which increases the rate of reaction. Can react with phenols.

Question 25

What are the reactions of acyl chlorides?

Answer 25

-React with alcohols to form esters and HCl gas
-React with phenols to form esters and HCl gas
-React with water (violently) to form carboxylic acids and HCl gas
-React with ammonia/amines to form amides
!!ACID ANHYDRIDES HAVE VERY SIMILAR REACTIONS!!