Organic and Biological Chemistry

Aldehydes and Ketones

Organic and Biological Chemistry 4.4 Aldehydes and Ketones1

Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Aldehydes and Ketones2

Carbonyl functional groupAldehyde: terminal carbonKetone: non terminal carbonStage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Aldehydes and KetonesAldehydes are prepared by a controlled oxidation of the corresponding primary alcohol. The aldehyde is distilled off as it forms to prevent further oxidation.

3Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Aldehydes and KetonesAldehydes are oxidised by acidified dichromate ions to the corresponding carboxylic acid.

4Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Aldehydes and KetonesKetones are prepared by the oxidation of secondary alcohols. No further oxidation occurs.

5Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Aldehydes and KetonesWhen heated with Tollens 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

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Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Aldehydes and KetonesKetones (and alcohols) do not oxidise with Tollens 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.7Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/20128

Vanillin

Tetracycline (antibiotic)Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Organic and Biological Chemistry 4.5 Carboxylic Acids9

Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Carboxylic Acids10

Carboxyl groupCarboxylic acids can be prepared by oxidation of primary alcohols or aldehydes with excess acidified dichromate solution.

Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Carboxylic AcidsCarboxylic acids are weak acidsIf they are soluble in water then they will partially ionise to form hydronium and carboxylate ions. RCOOH + H2O H3O+ + RCOOEquilibrium position favours reactants.11

Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Carboxylic AcidsCarboxylic acids react readily with bases such as:

Hydroxides and Oxides (Products: Salt & Water)RCOOH + OH RCOO + H2OCarbonates (Products: Salt ,Water and CO2)2RCOOH+CO32 2RCOO +H2O+CO2Hydrogen carbonates (Products: Salt ,Water and CO2)RCOOH + HCO3 RCOO + H2O+CO212Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Carboxylic AcidsCarboxylate salts of sodium and potassium are water soluble due to strong ion-dipole interactions which form between the negative carboxylate ion and the water molecules13

Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Ion dipole interactionsStrongest type of secondary interactionOccurs between a full positive or negative charge (ion) and a polar moleculeCommon between carboxylate ions and water or protonated amines and water14Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Carboxylic AcidsMany 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. 15

Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/201216

Salicylic Acid

Citric AcidStage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Organic and Biological Chemistry 4.6 Amines17

Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Amines18Based on ammonia

1o (primary) amine

2o (secondary) amineStage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Amines19

3o (tertiary) amineAmines tend to have unpleasant odours, often fishy.Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012AminesLike ammonia, amines can act as a base accepting a proton from an acidNH3 + H+ NH4+RNH2 + H+ RNH3+The product of this reaction is referred to as the protonated form of the amineThe protonated form is soluble in water due to ion dipole interactions between the protonated amine ion and water

20Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012AminesMany drugs (eg. Anaesthetics) contain amine functional groupsThese drugs are insoluble in water and so would not be effective if administered as the amineBy protonating these drugs they are able to dissolve in water within the body and so can act21

Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/201222

Nicotine

Methyl Orange

Chlorphenamine(Antihistamine)Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Organic and Biological Chemistry 4.7 Esters23

Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Esters24Similar structure to carboxylic acidsHydrogen on carboxyl group replaced by alkyl groupFruity odour

Ester functional groupAlcoholAcid

Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Naming EstersIdentify the alcohol carbon chain and the carbon chain from the acid.Name the alcohol part first followed by the acid

25Ethyl pentanoate

Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/201226

Aspirin (Acetyl Salicylic Acid)

Methyl Cinnamate (Strawberry)

Oil of Wintergreen (Methyl Salicylic Acid)Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Production of EstersEsters are formed by the reaction of a carboxylic acid and alcoholThis 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

27Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012

28Reflux

Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Production of Esters29The 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

Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Production of EstersThe ester can be separated from the mixture using a separating funnelThe mixture is washed with sodium bicarbonate which ensures the acid dissolves in the water layer30

Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Production of EstersThe aqueous layer which contains any unreacted alcohol and the sodium carboxylate salt can be tapped off leaving the organic layerThis layer is then distilled and the ester is collected at the appropriate tb31

Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012

32Distillation

Stage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Reactions of EstersIf an ester is refluxed with aqueous acid or base, it undergoes hydrolysisIn acidic conditions the products formed are a carboxylic acid and an alcohol. The reaction mixture is refluxed with sulfuric acid as the catalystThis is the reverse of esterification33

Acidic conditionsStage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012Reactions of EstersIn alkaline conditions the products formed are the carboxylate ions and the alcoholThe ester is refluxed with sodium hydroxide solution and the alcohol product can be separated from the sodium carboxylate salt by distillationThe carboxylic acid will reform if a solution of strong acid is added to the sodium carboxylate salt.

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Alkaline conditionsStage 2 Chemistry Lecture 15: Topics 4.4, 4.5, 4.6, 4.728/06/2012