26 The Aldehydes & Ketones - Science at St. Dominics

26 The Aldehydes & Ketones - Science at St. Dominics

Organic Chemistry 32 The Aldehydes & Ketones Leaving Certificate Chemistry The First 4 Aldehydes Structural Formulae Methanal: HCHO O group present 1 CarbonLong C H O H C H The First 4 Aldehydes

Structural Formulae Ethanal: CH3CHO O 2 Carbons Long H C H group present H O C C H H The First 4 Aldehydes Structural Formulae

Propanal: C2H5CHO O 3 Carbons Long H C H group present H H O C C C H H

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

C C C H H H H O H C Benzaldehyde At room temperature it is a colourless liquid with a characteristic and pleasant almondlike odour Physical Properties of the aldehydes 1. Use electronegativity differences to predict what kinds of bonds are present in an aldehyde such as ethanal. HINT USE THE RULES 2. Can you predict whether an aldehyde or its corresponding

alkane would have a higher boiling point? HINT - Think about the intermolecular forces present 3. Can you explain why the boiling points of the aldehydes increase with the length of the chain? HINT - Think about the intermolecular forces present 4. 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 H H C H CC C group present

O C H C Nail Varnish H Remover H An isomer of propanal The First 2 Ketones Structural Formulae Butanone: CH3COC2H5 O An isomer of butanal 4 Carbons Long H

CC C group present H O H H C C C C H H H H Physical Properties of the ketones

1. Use electronegativity differences to predict what kinds of bonds are present in an ketones such as propanone. HINT - USE THE RULES 2. Can you predict whether an ketone or its corresponding alkane would have a higher boiling point? HINT - Think about the intermolecular forces present 3. Can you explain why the boiling points of the ketones increase with the length of the chain? HINT - Think about the intermolecular forces present 4. 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 Oxidation of a primary alcohol Methanol CH3OH H H C O Acidified Sodium

Dichromate OH H C C Methanal HCHO O H H OH Methanoic Acid HCOOH Excess H Oxidation of a primary alcohol Ethanol C2H5OH

H H H C C H H O H H C H C Acidified Sodium Dichromate OH OH

Excess Ethanoic Acid CH3COOH H H O C C H Ethanal CH3CHO H Oxidation of a primary alcohol H H

H OH H C C C H H H Propanoic Propanol Propanal Acid C2CH23H OH 5COOH 57CHO O OH Acidified Sodium

Dichromate Excess Oxidation of a primary alcohol H H H H H OH C C C C H H

H H O OH Butanoic Butanol Acid Butanal On reaction with acidified sodium dichromate In Excess Substitution using UV Light The Alkanes Ethane C2H6 + H2 - H2 The Chloroalkanes Chloroethane C2H5Cl + HCl , + Cl2

The Alkenes Ethene C2H4 + H2O - H2O Aluminium Oxide Catalyst The Polymers Polythene & Polypropene The Alcohols Ethanol C2H5OH The Alcohols Ethanol C2H5OH Acidified sodium dichromate Hydrogen, Nickel catalyst Reduction Oxidation The Aldehydes

Ethanal CH3CHO Acidified sodium Reduction dichromate Hydrogen, Oxidation Nickel catalyst The Carboxylic Acids Ethanoic Acid CH3COOH Oxidation of a secondary alcohol H H O OH H C C C

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

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

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

The Carboxylic Acids Ethanoic Acid CH3COOH No reaction occurs with a ketone Tests to distinguish between an aldehyde and a ketone Acidified Potassium Permanganate Add 5 cm3 of Acidified potassium H permanganate O H Add 2Ccm3 of C ethanal OH (aldehyde), heat and shake Test tube Heat H The pink colour turns colurless acid Ethanoico

formed No reaction occurs with a ketone Tests to distinguish between an aldehyde and a ketone Fehlings Test Add 1 cm3 of Fehlings No. 1 & 1 cmH3 of Fehlings No. 2 O solutions Test tube Heat H Add 1Ccm3 of C ethanal OH (aldehyde), heat and shake H A brick red precipitate is observedacid Ethanoic

formed No reaction occurs with a ketone Tests to distinguish between an aldehyde and a ketone Tollens Reagent Add 3 cm3 of Silver Nitrate 3 solution and 1 cm of Sodium H O Hydroxide solution H C C OH Add a few drops of ammonia solution and shake. Then add 4-5 drops H of ethanal and heat water bath Test tube Heat

Ethanoic A silver mirror isacid observed formed Watch video on you tube - http:// www.youtube.com/watch?v=TRFkU6442 oo See animations videos http://youtu.be/qDGCE-KXPhw fehlings test http://youtu.be/zFMsqcGdZCc silver mirror test And http://youtu.be/CMCVpE8p8yo

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