13 - Reaction Mechanisms

Organic Chemistry The Alcohols Leaving Certificate Chemistry The alcohols are a group of organic compounds in which one (or more) of the hydrogen atoms of an alkane have been replaced by an OH hydroxyl group. The First 4 Alcohols Structural Formulae Methanol: CH3OH 1 CarbonLong -OH Group present H H C H OH

The First 4 Alcohols Structural Formulae Ethanol: C2H5OH Other Uses -OH Group 2 Carbon Longest Chain C6H12O6 Glucose Present H H C H 2C2H5OH + 2 CO2 C OH Ethanol Produced in industry

by fermentation H H Fuel Solvent Thermometer The First 4 Alcohols Structural Formulae Propanol: C3H7OH 3 Carbon Longest Chain -OH Group Present H H H H C

C H C H H H OH The First 4 Alcohols Structural Formulae Butanol: C4H9OH 4 Carbon Longest Chain H -OH Group Ptresent H

H H H C C C C H H H H OH Primary & Secondary Alcohols A primary secondary alcohol

alcohol is anisalcohol an alcohol in which in the carbon which the carbon atom that atomisthat bonded is bonded to theto OH (hydroxyl) the OH (hydroxyl) group is group itselfisalso itself bonded also to ONE other bonded to TWO carbon otheratom

carbon atoms. H H H H Propan-2-ol Propan-1-ol C C C H OH H H H OH Physical

Properties of the Alcohols Would you expect alcohols to have higher boiling points than alkanes/ Why? Comparing the boiling points of the alkanes and the alcohols Alcohols 2006 Q. 10 (c) 450 119 K 400 300 250 200 150 226.5 K 350 Liquid Gas

100 50 1 2 3 4 Number of Carbons Boiling point in Kelvins Alkanes Why does each alcohol have a higher boiling point than its corresponding alkane? Each alcohol has a higher relative molecular mass than its corresponding alkane 2006 Q. 10 (c) (7) Alcohols have strong intermolecular hydrogen bonding forces whereas alkanes are

influenced by much weaker Van Der Waals forces. H H C O H + H H O H C H H

Why is the difference in boiling points between methane and methanol 226.5 K whilst the difference in boiling points between butane and butanol is only 119 K? Because the strength of the hydrogen bonding is much weaker in butanol than it is in methanol 2006 Q. 10 (c) (6) This helps to explain why butanol is virtually insoluble (slightly soluble) in water whereas methanol is very soluble in water Would you expect all members of the alcohol family be equallyalcohols soluble in Would youtoexpect water? Why? to be soluble in water/ Why? Chemical Reactions

of the Alcohols Combustion Combustion CH3OH CO2 2 H2 O Oxygen Carbon Dioxide Water C2H5OH 3 O2 2 CO2 3 H2 O Ethanol

Oxygen Carbon Dioxide Water Methanol 1 O2 Chemical Reactions of the Alcohols Elimination Dehydration (elimination) H H H C

C H H H H C Ethanol C OH Aluminium OxideH [catalyst] Al2O3 This is an elimination reaction 1. Formation of a saturated compound 2. Loss of a small Ethene

H H2O Water 2007 Q. 8 (a) (6) Elimination reactions of alcohols Draw the structural formulas and name the products of an elimination reaction to 1. Propanol 2. Butanol Dehydration (elimination) Propanol H H H H C C

C H H H Aluminium H H C H OH C C Oxide C H2O

Water H H Propene Dehydration (elimination) Butanol H H H H H C C C C H

H H H H H C C H H H C H C H OH Aluminium Oxide

H Butene H2O Water Chemical Reactions of the Alcohols Oxidation 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 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 Chemical Reactions of the Alcohols The reaction of Reaction of ethanol with sodium H H H C C H

H Na 2 O Hydrogen Sodium H Sodium Ethoxide Ethanol C2H5OH Na Ethanol Sodium C2H5ONa Sodium Ethoxide

H2 Hydrogen Chemical Reactions of the Alcohols Reaction with an acid Esterification H H O C C O H H H Ethanoic

Acid CH3COOH Ethyl Group Ethyl Ethanoate HCH HCOOC H 2 5 CH COOC H CH3COOH 3 3 2 5 O C C2H5OH H C H H H2SO4 Ethanol C2H H25O

OH Esterification H H H O C C C O H H Methyl H Propanoate C2H5COOCH3 H

O C H H H 2O H Propanoic Acid C2H5COOH Methyl Group Methano l CH3OH 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

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