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Organic and Biological Chemistry . 4.4 Aldehydes and Ketones. Aldehydes and Ketones. Carbonyl functional group Aldehyde: terminal carbon Ketone: non terminal carbon. Aldehydes and Ketones.

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organic and biological chemistry

Organic and Biological Chemistry

4.4 Aldehydes and Ketones

aldehydes and ketones
Aldehydes and Ketones
  • Carbonyl functional group
  • Aldehyde: terminal carbon
  • Ketone: non terminal carbon
aldehydes and ketones1
Aldehydes and Ketones
  • Aldehydes are prepared by a controlled oxidation of the corresponding primary alcohol. The aldehyde is distilled off as it forms to prevent further oxidation.
aldehydes and ketones2
Aldehydes and Ketones
  • Aldehydes are oxidised by acidified dichromate ions to the corresponding carboxylic acid.
aldehydes and ketones3
Aldehydes and Ketones
  • Ketones are prepared by the oxidation of secondary alcohols. No further oxidation occurs.
aldehydes and ketones4
Aldehydes and Ketones
  • When heated with Tollen’s reagent (ammoniacal silver nitrate), aldehydes are oxidised to carboxylate ions.
  • RCHO  RCOO–
  • The silver diamine ion is reduced to metallic silver which can be deposited on the test tube giving a silver mirror.
  • Ag(NH3)2+  Ag
aldehydes and ketones5
Aldehydes and Ketones
  • Ketones (and alcohols) do not oxidise with Tollen’s reagent.
  • The silver mirror test is commonly used to identify between aldehydes and ketones.
  • It can also be used to identify between an aldehyde and alcohol where dichromate ions would react with both.
carboxylic acids
Carboxylic Acids

Carboxyl group

  • Carboxylic acids can be prepared by oxidation of primary alcohols or aldehydes with excess acidified dichromate solution.
carboxylic acids1
Carboxylic Acids
  • Carboxylic acids are weak acids
  • If they are soluble in water then they will partially ionise to form hydronium and carboxylate ions.
  • RCOOH + H2O  H3O+ + RCOO–
  • Equilibrium position favours reactants.
carboxylic acids2
Carboxylic Acids
  • Carboxylic acids react readily with bases such as:
  • Hydroxides and Oxides(Products: Salt & Water)

RCOOH + OH–  RCOO– + H2O

  • Carbonates (Products: Salt ,Water and CO2)

2RCOOH+CO32– 2RCOO– +H2O+CO2

  • Hydrogen carbonates (Products: Salt ,Water and CO2)

RCOOH + HCO3– RCOO– + H2O+CO2

carboxylic acids3
Carboxylic Acids
  • Carboxylate salts of sodium and potassium are water soluble due to strong ion-dipole interactions which form between the negative carboxylate ion and the water molecules
ion dipole interactions
Ion dipole interactions
  • Strongest type of secondary interaction
  • Occurs between a full positive or negative charge (ion) and a polar molecule
  • Common between carboxylate ions and water or protonated amines and water
carboxylic acids4
Carboxylic Acids
  • Many drugs including (aspirin and other painkillers) contain a carboxyl group. These drugs are often mixed with solid sodium hydrogen carbonate which converts the acid to the water soluble carboxylate on mixing with water.
  • This makes the drug easier to take and quicker acting that it would be in its insoluble form.
slide16

Citric Acid

Salicylic Acid

amines

1o (primary) amine

  • 2o (secondary) amine
Amines
  • Based on ammonia
amines1

3o (tertiary) amine

Amines
  • Amines tend to have unpleasant odours, often fishy.
amines2
Amines
  • Like ammonia, amines can act as a base accepting a proton from an acid
  • NH3 + H+→ NH4+
  • RNH2 + H+ RNH3+
  • The product of this reaction is referred to as the protonated form of the amine
  • The protonated form is soluble in water due to ion dipole interactions between the protonated amine ion and water
amines3
Amines
  • Many drugs (eg. Anaesthetics) contain amine functional groups
  • These drugs are insoluble in water and so would not be effective if administered as the amine
  • By protonating these drugs they are able to dissolve in water within the body and so can act
slide22

Nicotine

Chlorphenamine

(Antihistamine)

Methyl Orange

esters

Ester functional group

Acid

Alcohol

Esters
  • Similar structure to carboxylic acids
  • Hydrogen on carboxyl group replaced by alkyl group
  • Fruity odour
naming esters
Naming Esters
  • Identify the alcohol carbon chain and the carbon chain from the acid.
  • Name the alcohol part first followed by the acid
  • Ethyl pentanoate
slide26

Methyl Cinnamate (Strawberry)

Aspirin (Acetyl Salicylic Acid)

Oil of Wintergreen (Methyl Salicylic Acid)

production of esters
Production of Esters
  • Esters are formed by the reaction of a carboxylic acid and alcohol
  • This reaction is called ESTERIFICATION but can also be referred to as a CONDENSATION reaction because water is one of the products.
  • The reaction is slow at room temp and so the reaction mixture must be refluxed for an extended period and concentrated sulfuric acid is used as the catalyst
  • This is an equilibrium reaction
production of esters1
Production of Esters
  • The yield of the ester can be increased by using excess of one of the reagents. (Usually the alcohol because it is cheaper)
  • Large carbon chains (R groups) on the acid and alcohol decrease the yield of ester
production of esters2
Production of Esters
  • The ester can be separated from the mixture using a separating funnel
  • The mixture is washed with sodium bicarbonate which ensures the acid dissolves in the water layer
production of esters3
Production of Esters
  • The aqueous layer which contains any unreacted alcohol and the sodium carboxylate salt can be tapped off leaving the organic layer
  • This layer is then distilled and the ester is collected at the appropriate tb
reactions of esters
Reactions of Esters
  • If an ester is refluxed with aqueous acid or base, it undergoes hydrolysis
  • In acidic conditions the products formed are a carboxylic acid and an alcohol. The reaction mixture is refluxed with sulfuric acid as the catalyst
  • This is the reverse of esterification

Acidic conditions

reactions of esters1
Reactions of Esters
  • In alkaline conditions the products formed are the carboxylate ions and the alcohol
  • The ester is refluxed with sodium hydroxide solution and the alcohol product can be separated from the sodium carboxylate salt by distillation
  • The carboxylic acid will reform if a solution of strong acid is added to the sodium carboxylate salt.

Alkaline conditions