[CHEM] Chapter 11.4 - Alcohols

1 DARRELL ER (COPYRIGHTED) © TOPIC 11.4: ALCOHOLS DARRELL ER (COPYRIGHTED) ©

2 CHAPTER ANALYSIS THE ABOUT MASTERY EXAM WEIGHTAGE • Important topic • Take note of alcohol’s chemical reactions • Alcohols are commonly tested • Understand how fermentation works and the conditions needed • Heavy overall weightage • Entire Organic Chemistry portion accounts for 15- 20% of each year’s Chemistry paper DARRELL ER (COPYRIGHTED) ©

3 ALCOHOLS HOMOLOGOUS SERIES FUNCTIONAL GROUP GENERAL FORMULA KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

4 Alcohols Alcohols have the general formula CnH2n+1OH and can be identified by the hydroxyl -OH functional group. Functional group Alcohols have the hydroxyl -OH functional group. Isomers Isomerism can occur in alcohols that contain at least three carbon atoms. Isomers have the same molecular formula and similar chemical properties. However, isomers have different physical properties such as different melting and boiling points and densities. DARRELL ER (COPYRIGHTED) © Name Carbon atoms Molecular Formula Full Structural Formula Condensed structural formula Methanol 1 CH3OH CH3-OH Ethanol 2 C2H5OH CH3CH2-OH Propanol 3 C3H7OH CH3CH2CH2-OH Butanol 4 C4H9OH CH3 CH2CH2CH2- OH

5 ALCOHOLS PHYSICAL PROPERTIES PRODUCTION OF ALCOHOL CHEMICAL REACTIONS KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

6 PHYSICAL PROPERTIES DARRELL ER (COPYRIGHTED) © Physical property Reasoning Melting and boiling points As the number of carbon atoms in the alcohols increases, the melting and boiling points of alcohols increases as well. As the number of carbon atoms in an alcohol increases, the size of the molecules are bigger and have stronger intermolecular forces of attraction between each other. As such, more heat energy is needed to overcome the intermolecular forces of attraction between the alcohol molecules. Hence, larger alcohol containing more carbon atoms will have higher melting and boiling points. Volatility As the number of carbon atoms in the alcohol increases, the volatility of alcohol decreases. (similar to m.p. & b.p.) With a higher relative molecular mass, there would be stronger intermolecular forces of attraction between the alcohol molecules. As such, more energy is needed to overcome the intermolecular forces of attraction between the alcohol molecules. Hence, larger alcohol molecules are less likely to evaporate in room temperature. Density As the number of carbon atoms in the alcohols increases, the density of alcohols increases. Viscosity As the number of carbon atoms in the alcohols increases, the viscosity of alcohols decreases. (more difficult to flow) Alcohols with longer hydrocarbon chains flow less easily as they tend to get stuck together. Flammability As the number of carbon atoms in the alcohols increases, the flammability of alcohols decreases. (more difficult to burn) Solubility Alcohols are soluble in water, but as the number of carbon atoms increases, solubility in water decreases.

7 PRODUCTION OF ALCOHOL 1) Fermentation Fermentation is a chemical reaction where glucose/sugar are broken down by micro-organisms into smaller molecules such as alcohol and carbon dioxide. For instance, yeast contains enzymes that are used as catalyst for the breakdown of glucose C6H12O6 into ethanol C2H5OH and carbon dioxide. glucose  ethanol + carbon dioxide (in the presence of yeast) C6H12O6  2 C2H5OH + 2 CO2 MAKING ALCOHOL DARRELL ER (COPYRIGHTED) © PRODUCTION OF ALCOHOLS 1) Fermentation 1) Manufacture of ethanol from ethene

8 PRODUCTION OF ALCOHOL 2) Manufacture of ethanol from ethene (Hydration) To produce alcohol, alkene and steam are reacted together at a temperature of 300°C and at 60 atm. Phosphoric(V) acid is used as a catalyst for the reaction. The following equation below shows the reaction between ethene and steam. Uses of ethanol Ethanol is used in alcoholic drinks such as beer and wine. Ethanol is used as a organic solvent for many organic compounds. Ethanol has high volatility and it is an ideal solvent for perfume and deodorants. As it can undergo complete combustion to form carbon dioxide and water, ethanol is used as a clean fuel. MAKING ALCOHOL DARRELL ER (COPYRIGHTED) © PRODUCTION OF ALCOHOLS 1) Fermentation 1) Manufacture of ethanol from ethene

9 1) Combustion In the presence of excess oxygen, an alcohol would undergo complete combustion, producing carbon dioxide and water. If there is insufficient oxygen present for complete combustion, the alkene undergoes incomplete combustion to produce water and carbon monoxide instead. Soot (carbon) could also be produced as a by-product during incomplete combustion. 2) Oxidation Alcohols will be oxidised to form carboxylic acids in the presence of a strong oxidising agent. Oxidising agents: KMnO4 (purple to colourless) K2Cr2O7 (orange to green) For example, ethanol can be oxidised to ethanoic acid: CHEMICAL REACTIONS DARRELL ER (COPYRIGHTED) © CHEMICAL REACTIONS OF ALCOHOLS 1) Combustion 1) Oxidation 1) Esterification

10 3) Esterification In the presence of a catalyst, alcohols will react with carboxylic acids to form esters. Conditions: Concentrated H2SO4, heating under reflux CHEMICAL REACTIONS DARRELL ER (COPYRIGHTED) © CHEMICAL REACTIONS OF ALCOHOLS 1) Combustion 1) Oxidation 1) Esterification