13.4 Carbonyl compounds

• Chemistry
• Secondary Education
• Age 12,13

CARBONYL COMPOUNDS

Organic Chemistry

12 March 2024

• participate in the hinge-point discussion
• explain the mechanism of the reactions in this session
• formulate a conclusion from a set of reactions

Learning expectations

CARBONYL COMPOUNDS

Organic Chemistry

12 March 2024

Identify one concept you
learned from the
previous sessions.

CARBONYL COMPOUNDS

Organic Chemistry

12 March 2024

• Compounds that contain the C=O (carbonyl) group

CARBONYL COMPOUNDS

EXAMPLES

CARBONYL COMPOUNDS

Organic Chemistry

12 March 2024

• have higher boiling points than the alkanes with similar Mr 
• boiling points increase with increasing carbon atoms
• permanent dipole-dipole forces are also present due to carbonyl compounds being polar
• Methanal and ethanal are gases at room temperature, while others are liquids.
• soluble in water = decreases with increasing carbon atoms

Properties of Carbonyl compounds

CARBONYL COMPOUNDS

Organic Chemistry

12 March 2024

Which of these could be the best oxidising agent?

acid. potassium manganate (VII)

acid. potassium dichromate

hydrochloric acid

• Aldehydes and ketones can be made by oxidising primary and secondary alcohol. The oxidising agent used is either acidified potassium dichromate(VI), K2Cr2O7 or acidified potassium manganate(VII), KMnO4.

Preparation of Aldehydes and Ketones

• The primary alcohol used must be in excess and heated under reflux with acidified K2Cr2O7/KMnO4. The aldehyde formed must be distilled off as soon as possible.
• Under these conditions, a primary alcohol is oxidised to an aldehyde. 

Preparation of aldehydes

because 

______________ involves heating the chemical reaction for a specific amount of time, while continually cooling the vapour produced back into liquid form, using a condenser.

1. In situ
2. Reflux
3. In vitro

• The secondary alcohol is heated under reflux with acidified K2Cr2O7/KMnO4.
• Under these conditions, a secondary alcohol is oxidised to a ketone.  
  

Preparation of ketones

CARBONYL COMPOUNDS

Organic Chemistry

12 March 2024

• C=O bond of the carbonyl group = highly polarised due to oxygen atom being more electronegative
• carbonyl compounds = undergo nucleophilic addition

Reactivity of carbonyl compounds

CARBONYL COMPOUNDS

Organic Chemistry

12 March 2024

• Reduction
• Oxidation
• Reaction with Hydrogen cyanide, HCN

Reactions of Aldehydes and Ketones

• Reagent : Lithium tetrahydridoaluminate, LiAlH4 or sodium tetrahydridoborate, NaBH4
• Condition : For LiAlH4 - in dry ether; For NaBH4 - in aqueous alcoholic solution
• Product : Aldehyde - primary alcohol; Ketone - secondary alcohol

REDUCTION

it can also happen with water molecule as a nucleophile

REDUCTION

Aldehyde

Ketone

Due to the reactivity of LiAlH4, it cannot be used in the presence of water or

alcohol. It must be carried out in solution in a carefully dried ether such as ethoxyethane(diethyl ether).

CARBONYL COMPOUNDS

Organic Chemistry

12 March 2024

• Reagent : Acidified potassium dichromate(VI), K2Cr2O7 or acidified potassium manganate(VI), KMnO4
• Condition : Heat under reflux
• Product : Aldehyde - Carboxylic acid; Ketone - Will not be oxidised.

OXIDATION

Aldehyde

Ketone

• Reagent : Sodium/potassium cyanide, NaCN and a little sulfuric acid, H2SO4
• Condition : Room temperature
• Product : Hydroxynitriles

REACTION WITH HYDROGEN CYANIDE

Aldehyde

Ketone

Hydrogen cyanide is not used alone because it is a poisonous gas. Instead, it is produced from the reaction between sodium/potassium cyanide and sulfuric acid. The solution will contain hydrogen cyanide and some free cyanide ions.

Reaction mechanism

Hydrogen cyanide is not used alone because it is a poisonous gas. Instead, it is produced from the reaction between sodium/potassium cyanide and sulfuric acid. The solution will contain hydrogen cyanide and some free cyanide ions.

CARBONYL COMPOUNDS

Organic Chemistry

12 March 2024

• Reagent : Brady's reagent = solution of the 2,4-dinitrophenylhydrazine in methanol and sulfuric acid

Test for Carbonyl Group

2,4-dinitrophenylhydrazine or 2,4-DNPH can be used to detect the presence of carbonyl group, C=O. 

• Reagent : Tollens' reagent = diamminesilver(I) ions, [Ag(NH3)2]+

Test for Aldehydes

• When a few drops of aldehyde are added to the freshly prepared Tollens' reagent and warmed in a water bath for a few minutes, a grey precipitate or a silver mirror is observed only if aldehyde is present.

Aldehydes will reduce the diamminesilver(I) ions to metallic silver, aldehyde itself is oxidised to a salt of carboxylic acid.

Since ketones will not be oxidised, it will not reduce it to metallic silver.

it can also happen with water molecule as a nucleophile

• Reagent : Fehling's solution =  copper(II) ions complexed with tartrate ions in sodium hydroxide solution

Test for Aldehydes

Complexing the copper(II) ions with tartrate ions prevents precipitation of copper(II) hydroxide. It is a blue solution.

CARBOXYLIC ACIDS AND DERIVATIVES

Organic Chemistry

12 March 2024

• compounds that contain the -COOH group

Carboxylic Acids

• have higher melting and boiling points than the corresponding alcohols
• boiling points increase with increasing carbon atoms
• soluble in water = decreases with increasing carbon atoms

Properties of Carboxylic acids

CARBOXYLIC ACIDS AND DERIVATIVES

Organic Chemistry

12 March 2024

There are three ways to produce carboxylic acids: 

• Oxidation of primary alcohol.
• Oxidation of aldehyde.
• Acidic/alkaline hydrolysis of nitrile.

Preparation of carboxylic acids

• When nitrile is heated under reflux with a dilute acid such as dilute hydrochloric acid, carboxylic acid will be formed.

Acidic hydrolysis of nitriles

• When nitrile is heated under reflux with an alkali such as sodium hydroxide, salt of carboxylic acid (carboxylate salt) is produced.
• Ethanoate ion can be converted to ethanoic acid by the addition of acid. 

 Alkaline hydrolysis of nitrile

CARBOXYLIC ACIDS AND DERIVATIVES

Organic Chemistry

12 March 2024

• Acidic, because they can donate a proton to form carboxylate ions and hydroxonium ions. The presence of hydroxonium ions makes the solution acidic.
• Weakly acidic

Acidity of carboxylic acids

CARBOXYLIC ACIDS AND DERIVATIVES

Organic Chemistry

12 March 2024

• Reaction with bases
• Reaction with metals
• Reaction with carbonates and hydrogencarbonates
• Converting carboxylic acids to acyl chlorides 

Reactions of Carboxylic acids

• Reagent : a base such as sodium hydroxide
• Product : a carboxylate salt and water

Reaction with bases

it can also happen with water molecule as a nucleophile

• Reagent : reactive metals such as sodium
• Product : a carboxylate salt and hydrogen gas

Reaction with metals

it can also happen with water molecule as a nucleophile

• Reagent : carbonates and hydrogencarbonates
• Product : a carboxylate salt, carbon dioxide gas and water

Reaction with carbonates and hydrogencarbonates

it can also happen with water molecule as a nucleophile

• have the -OH in the -COOH group of the carboxylic acid replaced by chlorine
• very reactive and can be used to produce a range of other organic compounds

What are ACYL CHLORIDES?

Example

• Reaction with phosphorus(III) chloride, PCl3
• Reaction with phosphorus(V) chloride, PCl5
• Reaction with thionyl chloride, SOCl2.

Three methods to produce acyl chlorides 

 Reaction with phosphorus(III) chloride, PCl3 

 Reaction with phosphorus(V) chloride, PCl5

 Reaction with thionyl chloride, SOCl2

CARBOXYLIC ACIDS AND DERIVATIVES

Organic Chemistry

12 March 2024