RPA - Carbonyls

Question 1

What causes reactivity of carbonyls, therefore how do they react?

Answer 1

Polar C=O bond causes nucleophilic addition by breaking double bond

Question 2

What type of compounds are classed as carbonyls?

Answer 2

Aldehydes and Ketones

Question 3

On oxidation of a primary alcohol, which two possible products are possible? Give conditions and reagents for each.

Answer 3

Immediate distillation - aldehyde. H+/Cr2O72-

Reflux - carboxylic acid. H+/Cr2O72-

Question 4

Give the equation for the oxidation of ethanol to form ethanal

Answer 4

CH3CH2OH + [O] -> CH3CHO + H2O

Question 5

Give the equation for the oxidation of ethanol to form ethanoic acid

Answer 5

CH3CH2OH + 2[O] -> CH3COOH + H2O

Question 6

Give the equation for the oxidation of ethanal to form ethanoic acid

Answer 6

CH3CHO + [O] -> CH3COOH

Question 7

Give the equation for the oxidation of propan-2-ol to form propanone

Answer 7

CH3CHOHCH3 + [O] -> CH3C=OCH3 + H2O

Question 8

What type of reactant is NaBH4?

Answer 8

Reducing agent. It produces H-

Question 9

By which mechanism does NaBH4 react with aldehydes and ketones?

Answer 9

nucleophilic addition

Question 10

Talk through the steps involved in the reaction of propanone and NaBH4

Answer 10

.

Question 11

What is the product when aldehydes and ketones react with NaBH4?

Answer 11

Aldehydes - primary alcohols

Ketones - secondary alcohols

Question 12

Give the equation for the reduction of a ethanal to ethanol

Answer 12

CH3CHO + 2[H] – > CH3CH2OH

Question 13

Give the equation for the reduction of propanone to propan-2-ol.

Answer 13

CH3C=OCH3 + 2[H] – > CH2CHOHCH3

Question 14

What is Tollens reagent made from?

Answer 14

AgNO3 + excess NH3 in NaOH solution

Question 15

What type of reagent is Tollens

Answer 15

Mild oxidising agent

Question 16

What type of compounds can tollens react with?

Answer 16

Aldehydes

Question 17

What is observed when Tollens reacts with aldehydes, ketones and alcohols.

Answer 17

It forms a silver mirror/dark precipitate when it is reduced to Ag(s)

It is only a mild oxidising agent, so will not react with alcohols or ketones.

Question 18

What is Brady’s Reagent?

Answer 18

2,4-dinitrophenylhydrazine

Question 19

What does Brady’s reagent do when reacted with aldehydes and ketones? What is observed?

Answer 19

It forms orange precipitates whos melting points can be observed.

Question 20

What is the reason for using Brady’s reagent?

Answer 20

Boiling points of volatile aldehydes/ketones can be hard to find experimentally as many are low.

Reaction with 2,4-DNPH causes the melting point to be above room temperature, hence it can be measured using thiele tube.