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13.4 Carbonyl compounds

CARBONYL COMPOUNDS
Organic Chemistry
12 March 2024
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ChemistrySecondary EducationAge 12,13

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CARBONYL COMPOUNDS
Organic Chemistry
12 March 2024

Slide 1 - Tekstslide

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  • 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

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CARBONYL COMPOUNDS
Organic Chemistry
12 March 2024

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Identify one concept you
learned from the
previous sessions.

Slide 4 - Woordweb

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CARBONYL COMPOUNDS
Organic Chemistry
12 March 2024

Slide 5 - Tekstslide

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

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EXAMPLES

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CARBONYL COMPOUNDS
Organic Chemistry
12 March 2024

Slide 9 - Tekstslide

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  • 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

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CARBONYL COMPOUNDS
Organic Chemistry
12 March 2024

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Which of these could be the best oxidising agent?
acid. potassium manganate (VII)
acid. potassium dichromate
hydrochloric acid

Slide 12 - Poll

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  • 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

Slide 13 - Tekstslide

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  • 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

Slide 14 - Tekstslide

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.
A
In situ
B
Reflux
C
In vitro

Slide 15 - Quizvraag

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  • 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

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CARBONYL COMPOUNDS
Organic Chemistry
12 March 2024

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  • 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

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CARBONYL COMPOUNDS
Organic Chemistry
12 March 2024

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  • Reduction
  • Oxidation
  • Reaction with Hydrogen cyanide, HCN
Reactions of Aldehydes and Ketones

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  • 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

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it can also happen with water molecule as a nucleophile
REDUCTION
Aldehyde
Ketone

Slide 22 - Tekstslide

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

Slide 23 - Tekstslide

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  • 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

Slide 24 - Tekstslide

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  • Reagent : Sodium/potassium cyanide, NaCN and a little sulfuric acid, H2SO4
  • Condition : Room temperature
  • Product : Hydroxynitriles
REACTION WITH HYDROGEN CYANIDE
Aldehyde
Ketone

Slide 25 - Tekstslide

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

Slide 26 - Tekstslide

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

Slide 27 - Tekstslide

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

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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.

Slide 29 - Tekstslide

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.

Slide 30 - Tekstslide

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

Slide 31 - Tekstslide

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

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  • compounds that contain the -COOH group
Carboxylic Acids

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  • 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

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CARBOXYLIC ACIDS AND DERIVATIVES
Organic Chemistry
12 March 2024

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There are three ways to produce carboxylic acids: 
  • Oxidation of primary alcohol.
  • Oxidation of aldehyde.
  • Acidic/alkaline hydrolysis of nitrile.
Preparation of carboxylic acids

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

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  • 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

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CARBOXYLIC ACIDS AND DERIVATIVES
Organic Chemistry
12 March 2024

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  • 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

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CARBOXYLIC ACIDS AND DERIVATIVES
Organic Chemistry
12 March 2024

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

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

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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

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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

Slide 45 - Tekstslide

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

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  • Reaction with phosphorus(III) chloride, PCl3
  • Reaction with phosphorus(V) chloride, PCl5
  • Reaction with thionyl chloride, SOCl2.
Three methods to produce acyl chlorides 

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 Reaction with phosphorus(III) chloride, PCl3 

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 Reaction with phosphorus(V) chloride, PCl5

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 Reaction with thionyl chloride, SOCl2

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CARBOXYLIC ACIDS AND DERIVATIVES
Organic Chemistry
12 March 2024

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