32 The Aldehydes & Ketones Organic Chemistry 32 The Aldehydes & Ketones Leaving Certificate Chemistry

The First 4 Aldehydes Structural Formulae Methanal: HCHO O group present ― ― 1 Carbon-Long ― C ― H O H C H

The First 4 Aldehydes Structural Formulae Ethanal: CH3CHO O ― ― 2 Carbons Long ― C ― H group present H O Acetaldehyde (systematically ethanal) is an organic chemical compound with the formula CH3 CHO, sometimes abbreviated by chemists as MeCHO (Me = methyl). It is one of the most important aldehydes, occurring widely in nature and being produced on a large scale industrially. Acetaldehyde occurs naturally in coffee, bread, and ripe fruit, and is produced by plants as part of their normal metabolism. It is also produced by oxidation of ethylene and is popularly believed to be a cause of hangovers from alcohol consumption.[4] Pathways of exposure include air, water, land or groundwater as well as drink and smoke.[5] H C C H H

The First 4 Aldehydes Structural Formulae Propanal: C2H5CHO O ― ― 3 Carbons Long ― C ― H group present H H O H C C C H H H

The First 4 Aldehydes Structural Formulae Butanal: C3H7CHO O ― ― 4 Carbons Long ― C ― H group present H H H O H C C C H C H H H

O H Benzaldehyde At room temperature it is a colourless liquid with a characteristic and pleasant almond-like odour C

Physical Properties of the aldehydes Use electronegativity differences to predict what kinds of bonds are present in an aldehyde such as ethanal. HINT - USE THE RULES Can you predict whether an aldehyde or its corresponding alkane would have a higher boiling point? HINT - Think about the intermolecular forces present Can you explain why the boiling points of the aldehydes increase with the length of the chain? HINT - Think about the intermolecular forces present Would the lower or higher members of the aldehydes be more soluble in water? HINT – water is polar. LIKE DISSOLVES LIKE

The First 2 Ketones Structural Formulae Propanone: CH3COCH3 O ― ― 3 Carbons Long C ― C ― C group present H O H Nail Varnish Remover H C C C H H H An isomer of propanal

The First 2 Ketones Structural Formulae Butanone: CH3COC2H5 O An isomer of butanal ― ― 4 Carbons Long C ― C ― C group present H O H H H C C C C H H H H

Physical Properties of the ketones Use electronegativity differences to predict what kinds of bonds are present in an ketones such as propanone. HINT - USE THE RULES Can you predict whether an ketone or its corresponding alkane would have a higher boiling point? HINT - Think about the intermolecular forces present Can you explain why the boiling points of the ketones increase with the length of the chain? HINT - Think about the intermolecular forces present Would the lower or higher members of the ketones be more soluble in water? HINT – water is polar. LIKE DISSOLVES LIKE

Formation of an aldehyde or ketone Oxidation of a primary or secondary alcohol

Oxidation of a primary alcohol Methanol CH3OH O H H Acidified Sodium Dichromate H C H H C OH Methanal HCHO H H O H C OH Excess Methanoic Acid HCOOH

Oxidation of a primary alcohol Ethanol C2H5OH H Acidified Sodium Dichromate H H H C C OH H H H H O H O H C C H Excess H C C OH Ethanoic Acid CH3COOH Ethanal CH3CHO H H

Oxidation of a primary alcohol Acidified Sodium Dichromate H H H Propanoic Acid C2H5COOH Propanol C3H7OH Propanal C2H5CHO Excess

Oxidation of a primary alcohol Butanol Butanal Butanoic Acid On reaction with acidified sodium dichromate In Excess

The Alkanes - H2 The Chloroalkanes + H2 The Alkenes + HCl , + Cl2 Substitution using UV Light Ethane C2H6 - H2 The Chloroalkanes + H2 Chloroethane C2H5Cl The Alkenes + HCl , + Cl2 Ethene C2H4 + H2O The Alcohols Ethanol C2H5OH - H2O Aluminium Oxide Catalyst The Polymers Polythene & Polypropene

The Alcohols The Aldehydes The Carboxylic Acids Ethanol C2H5OH Acidified sodium dichromate Hydrogen, Nickel catalyst Oxidation Reduction The Aldehydes Ethanal CH3CHO Acidified sodium dichromate Reduction Hydrogen, Nickel catalyst Oxidation The Carboxylic Acids Ethanoic Acid CH3COOH

Oxidation of a secondary alcohol Acidified Sodium Dichromate H H H Propanone Propan-2-ol Nail Varnish Remover Oxidation of a secondary alcohol produces a ketone

Oxidation of a secondary alcohol Acidified Sodium Dichromate H H H H Butanone Butan-2-ol Oxidation of a secondary alcohol produces a ketone

The Ketones The Alcohols The Aldehydes The Carboxylic Acids Oxidation of a secondary alcohol The Ketones Acidified sodium dichromate The Alcohols H2, Ni Reduction Propanone from propan-2-ol Ethanol C2H5OH Acidified sodium dichromate Hydrogen, Nickel catalyst Oxidation Reduction The Aldehydes Ethanal CH3CHO Acidified sodium dichromate Reduction Hydrogen, Nickel catalyst Oxidation The Carboxylic Acids Ethanoic Acid CH3COOH

Tests to distinguish between an aldehyde and a ketone Acidified Potassium Permanganate H Add 5 cm3 of Acidified potassium permanganate H O No reaction occurs with a ketone H Add 2 cm3 of ethanal (aldehyde), heat and shake H C C OH H The pink colour turns colurless Ethanoico acid formed CH3COOH Test tube Heat

Tests to distinguish between an aldehyde and a ketone Fehling’s Test H Add 1 cm3 of Fehling’s No. 1 & 1 cm3 of Fehling’s No. 2 solutions H O No reaction occurs with a ketone H H C C OH Add 1 cm3 of ethanal (aldehyde), heat and shake H A brick red precipitate is observed Ethanoic acid formed CH3COOH Test tube Heat

Tests to distinguish between an aldehyde and a ketone Tollen’s Reagent H Add 3 cm3 of Silver Nitrate solution and 1 cm3 of Sodium Hydroxide solution H O No reaction occurs with a ketone H H C C OH Add a few drops of ammonia solution and shake. Then add 4-5 drops of ethanal and heat water bath Ha;f reactions must be known H Ethanoic acid formed CH3COOH A “silver mirror” is observed Test tube Heat

Watch video on you tube - http://www.youtube.com/watch?v=TRFkU6442oo See animations videos http://youtu.be/qDGCE-KXPhw fehlings test http://youtu.be/zFMsqcGdZCc silver mirror test And http://youtu.be/CMCVpE8p8yo