Carbonyls: Aldehydes, Ketones and Carboxylic Acid

Question 1

How to make carbonyls?

Answer 1

Oxidising agent: Acidified potassium dichromate
Turns from orange to green

Aldehyde: From 1° Alcohol and distill
Ketone: From 2° Alcohol and reflux
Carboxylic Acid: From 1° alcohol and reflux

Question 2

How to make alcohols from carbonyls?

Answer 2

LiAlH4 in dry ether
Aldehyde/Carboxylic Acid = 1° Alcohol
Ketone = 2° Alcohol
Mechanism: Nucleophilic Addition

Question 3

Bonding between Ketones and Aldehydes

Answer 3

NO Hydrogen bonding
Only London forces as they do not have a δ+H

They can form Hydrogen bonds with water as H from water forms bond with δ- oxygen in carbonyl

Question 4

Test for aldehydes and ketones

Answer 4

Oxidising Agent: Tollens Reagent or Fehling’s Solution
Only positive for aldehydes

Fehlings: blue sol to red ppt
Tollens: colourless –> silver will form on walls of test tube

Question 5

Reactions of ketones and aldehydes with HCN

Answer 5

Reaction type: Nucleophilic Addition
Electrophile: :CN-
Reagent: KCN
Product: Hydroxynitrile (adds to carbon length) and chiral compound

Question 6

Iodoform reaction of ketones and aldehydes

Answer 6

Add Iodine solution then NaOH solution, creates a pale yellow ppt known as Triiodomethane

Question 7

Test for all carbonyl compounds

Answer 7

Reagent: 2,4-DNPH
Positive test: Yellow, orange or red ppt forms
Ppt formed can be re-crystallised and melting point determined
Carbonyls have sharp melting points

Question 8

Bonding in Carboxylic Acids

Answer 8

Can form hydrogen bonds with other C.Acid molecules
Can form hydrogen bonds with water
Increasing chain length = less soluble
highest m.p against alcohols, ketones and aldehydes

Question 9

Acylation of carboxylic acids

Answer 9

React with solid PCl5

CH3COOH + PCl5 –> CH3COCl + POCl3 + HCl

Question 10

Esterification

Answer 10

Carboxylic acid + Alcohol
Strong acid catalyst (conc H2SO4)
Carried under reflux
Forms ester and water

Question 11

Reactions of Acyl chlorides with

Water
Alcohol
Ammonia
Amines

Answer 11

nucleophilic addition-elimination

Water: Carboxlic Acid
Alcohol: ester
Ammonia: Amide
Amines: N-Substituted amide

Question 12

Hydrolysis of Esters

Answer 12

Acidic Conditions:
Adding water from acid produces alcohol and c.acid

Alkaline conditions:
Using NaOH as base
Carboxylate salt + Alcohol

Question 13

Condensation Polymerisation of Esters

Answer 13

Water molecule removed from reaction
Polyesters formed from dicarboxylic acid and diol
forms ester linkage of -COO-

polyesters can be broken down by hydrolysis due to polarity within polymer molecules