ALCOHOL

1. ALCOHOL Chemistry of -OH Dr Seemal Jelani

2. Propan- 1- ol Alcohols Propan- 2- ol Butan- 1- ol Butan - 1, 4 - diol Dr Seemal Jelani

3. These all have the formula C4H9OH butan-1-ol butan-2-ol 2-methylpropan-2-ol 2-methylpropan-1-ol Dr Seemal Jelani

4. Bond angles in alcohol groups Dr Seemal Jelani

5. Solubility in water The alcohol groups form hydrogen bonding which makes the short chain molecules soluble in water. The solubility in water decreases as the chain length increases. Dr Seemal Jelani

6. Ethanol Propan-1-ol Butan-1-ol Low-mass alcohols are soluble in water (because they hydrogen bond with water). As the hydrocarbon chain lengthens, the solubility decreases. This photo shows ethanol, propan-1-ol and butan-1-ol in water. The first two are completely miscible in water, while butan-1-ol is not miscible in water. Dr Seemal Jelani

7. Boiling Points of Alcohols Increases with molecular size due to increased instantaneous dipoles • Alcohols have higher boiling points than similar molecular mass alkanes • This is due to the added presence of inter-molecular hydrogen bonding • More energy is required to separate the molecules Dr Seemal Jelani

8. CLASSIFICATION OF ALCOHOLS Aliphatic • general formula CnH2n+1OH- provided there are no rings • the OH replaces an H in a basic hydrocarbon skeleton Structural differences • Alcohols are classified according to the environment of the OH group • Chemical behaviour, e.g oxidation, often depends on the structural type NB. Aliphatic - straight chain molecule (not a ring / cyclic) Dr Seemal Jelani

9. PRIMARY 1° TERTIARY 3° SECONDARY 2° Dr Seemal Jelani

10. Luca’s Reagent • Solution of anhydrous zinc chloride in concentrated hydrochloric acid • This solution is used to classify alcohols of low molecular weight. Dr Seemal Jelani

11. Distinguishing alcohols Lucas reagent can be used to distinguish between low mass primary, secondary and tertiary alcohols. Lucas reagent contains anhydrous zinc chloride dissolved in concentrated hydrochloric acid. It contains a very high concentration of chloride ions and the Zn2+ ion acts as a catalyst. Take 1–2 mL of Lucas reagent in a dry test tube, add a few drops of the alcohol and shake. If there is no reaction, place the test tube in a beaker of boiling water for a few minutes. Dr Seemal Jelani

12. Distinguishing alcohols - Lucas test Lucas reagent = conc. HCl and ZnCl2 Primary alcohol - remain unchanged Secondary alcohol - will turn cloudy but takes a bit of time tertiary alcohol - turns cloudy immediately Dr Seemal Jelani

13. Tertiary alcohols turn cloudy immediately. Once heated, the secondary alcohol quickly turned cloudy. The primary alcohol tube is unchanged. Dr Seemal Jelani

14. OXIDATION OF PRIMARY ALCOHOLS Primary alcohols are easily oxidised to aldehydes e.g. CH3CH2OH(l) + [O] ——> CH3CHO(l) + H2O(l) ethanol ethanal it is essential to distil off the aldehyde before it gets oxidised to the acid CH3CHO(l) + [O] ——> CH3COOH(l) ethanal ethanoic acid Dr Seemal Jelani

15. Practical details • The alcohol is dripped into a warm solution of acidified k2cr2o7 • Aldehydes have low boiling points - no hydrogen bonding - they distil off immediately • If it didn’t distil off it would be oxidised to the equivalent carboxylic acid • To oxidize an alcohol straight to the acid, reflux the mixture • Compound Formula Intermolecular bonding boiling point • Ethanol C2H5OH hydrogen bonding 78°C • Ethanal CH3CHO dipole-dipole 23°C • Ethanoic acid CH3COOH hydrogen bonding 118°C Dr Seemal Jelani

16. Oxidising a primary alcohol to an aldehyde Full oxidation is not wanted: use dilute acid and less dichromate. The reaction mixture is heated gently, ethanal vapourises (21°C) as soon as it is formed and distils over. This stops it being oxidised further to ethanoic acid. Dr Seemal Jelani

17. Apparatus for the oxidation of ethanol to ethanoic acid Dr Seemal Jelani

18. Oxidising a primary alcohol to a carboxylic acid reflux Distil to separate Dr Seemal Jelani

19. Oxidising a secondary alcohol to a ketone Dr Seemal Jelani

20. Oxidation of alcohols Primary and secondary alcohols are oxidised by acidified potassium dichromate. A beaker of hot water speeds up the reaction. There is no reaction with tertiary alcohols. Dr Seemal Jelani

21. Oxidation of alcohols Primary alcohols aldehydes Carboxylic acid Secondary alcohol Ketones Don’t oxidise Dr Seemal Jelani tertiary alcohol

22. Formation of ethanol by fermentation Conditionsyeast warm, but no higher than 37°C (optimum temp. for yeast) Advantages LOW ENERGY PROCESS USES RENEWABLE RESOURCES - PLANT MATERIAL SIMPLE EQUIPMENT Disadvantages SLOW PRODUCES IMPURE ETHANOL - will need distilling to purify BATCH PROCESS Dr Seemal Jelani

23. Formation of haloalkane Ethanol and PCl5 C2H5OH(l) + PCl5(s) C2H5Cl(g) + POCl3(l) + HCl(g) Phosphoryl chloride solid fumes Thionyl chloride Ethanol and SOCl2 C2H5OH(l) + SOCl2(l) C2H5Cl(g) + SO2(g) + HCl(g) Dr Seemal Jelani

24. Formation of ethanol from ethene AdvantagesFast Pure ethanol produced Continuous process Disadvantages high energy process Expensive plant required Uses non-renewable fossil fuels to make ethene Uses of ethanol alcoholic drinks SOLVENT - industrial alcohol / methylated spirits FUEL - petrol substitute in countries with limited oil reserves Dr Seemal Jelani

25. Dehydration of alcohols Reagent: concentrated sulphuric acid or passing the alcohol over aluminium oxide Dr Seemal Jelani

26. Reaction with sodium The reaction is similar to the reaction of alkali metals with water, but less vigorous. Dr Seemal Jelani

27. Esterification Catalyst: concentrated H2SO4 (dehydrating agent - it removes water causing the equilibrium to move to the right and increases the yield Conditions: reflux Dr Seemal Jelani

28. Esters Methyl Ethanoate Methyl Ethanoate Uses of esters Esters are fairly unreactive but that doesn’t make them useless Used as flavourings Naming esters Named from the alcohol and carboxylic acid which made them... CH3OH + CH3COOHCH3COOCH3+ H2O fromethanoic acidCH3COOCH3from methanol METHYLETHANOATE Dr Seemal Jelani