ALCOHOL Chemistry of -OH 5/12/2015Dr Seemal Jelani1

Alcohols Butan - 1, 4 - diol Butan- 1- ol Propan- 2- ol Propan- 1- ol 5/12/2015Dr Seemal Jelani2

These all have the formula C 4 H 9 OH butan-1-olbutan-2-ol 2-methylpropan-1-ol2-methylpropan-2-ol 5/12/2015Dr Seemal Jelani3

Bond angles in alcohol groups 5/12/2015Dr Seemal Jelani4

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. 5/12/2015Dr Seemal Jelani5

Low-mass alcohols are soluble in water (because they hydrogen bond with water). As the hydrocarbon chain lengthens, the solubility decreases. EthanolPropan-1-olButan-1-ol 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. 5/12/2015Dr Seemal Jelani6

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 5/12/2015Dr Seemal Jelani7

CLASSIFICATION OF ALCOHOLS Aliphatic general formula C n H 2n+1 OH - 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) 5/12/2015Dr Seemal Jelani8

5/12/2015Dr Seemal Jelani9 PRIMARY 1° SECONDARY 2° TERTIARY 3°

Luca’s Reagent Solution of anhydrous zinc chloride in concentrated hydrochloric acidzinc chloridehydrochloric acid This solution is used to classify alcohols of low molecular weight.alcohols 5/12/2015Dr Seemal Jelani10

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 Zn 2+ 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. 5/12/2015Dr Seemal Jelani11

Distinguishing alcohols - Lucas test Primary alcohol - remain unchanged tertiary alcohol - turns cloudy immediately Secondary alcohol - will turn cloudy but takes a bit of time Lucas reagent = conc. HCl and ZnCl 2 5/12/2015Dr Seemal Jelani12

Tertiary alcohols turn cloudy immediately. Once heated, the secondary alcohol quickly turned cloudy. The primary alcohol tube is unchanged. 5/12/2015Dr Seemal Jelani13

OXIDATION OF PRIMARY ALCOHOLS Primary alcohols are easily oxidised to aldehydes e.g. CH 3 CH 2 OH(l) + [O] ——> CH 3 CHO(l) + H 2 O(l) ethanol ethanal it is essential to distil off the aldehyde before it gets oxidised to the acid CH 3 CHO(l) + [O] ——> CH 3 COOH(l) ethanal ethanoic acid 5/12/2015Dr Seemal Jelani14

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 CH3CHOdipole-dipole 23°C Ethanoic acid CH3COOHhydrogen bonding 118°C 5/12/2015Dr Seemal Jelani15

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. 5/12/2015Dr Seemal Jelani16

Apparatus for the oxidation of ethanol to ethanoic acid 5/12/2015Dr Seemal Jelani17

Oxidising a primary alcohol to a carboxylic acid reflux Distil to separate 5/12/2015Dr Seemal Jelani18

Oxidising a secondary alcohol to a ketone 5/12/2015Dr Seemal Jelani19

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. 5/12/2015Dr Seemal Jelani20

Oxidation of alcohols Primary alcohols tertiary alcohol Secondary alcohol aldehydesCarboxylic acid Don’t oxidise Ketones 5/12/2015Dr Seemal Jelani21

Formation of ethanol by fermentation Conditions yeast warm, but no higher than 37°C (optimum temp. for yeast) AdvantagesLOW ENERGY PROCESS USES RENEWABLE RESOURCES - PLANT MATERIAL SIMPLE EQUIPMENT DisadvantagesSLOW PRODUCES IMPURE ETHANOL - will need distilling to purify BATCH PROCESS 5/12/2015Dr Seemal Jelani22

Formation of haloalkane Ethanol and PCl 5 C 2 H 5 OH (l) + PCl 5(s)  C 2 H 5 Cl (g) + POCl 3(l) + HCl (g) fumes solid Ethanol and SOCl 2 C 2 H 5 OH (l) + SOCl 2(l)  C 2 H 5 Cl (g) + SO 2(g) + HCl (g) 5/12/2015Dr Seemal Jelani23 Phosphoryl chloride Thionyl chloride

Formation of ethanol from ethene Advantages Fast Pure ethanol produced Continuous process Disadvantageshigh energy process Expensive plant required Uses non-renewable fossil fuels to make ethene Uses of ethanolalcoholic drinks SOLVENT - industrial alcohol / methylated spirits FUEL - petrol substitute in countries with limited oil reserves 5/12/2015Dr Seemal Jelani24

Dehydration of alcohols Reagent: concentrated sulphuric acid or passing the alcohol over aluminium oxide 5/12/2015Dr Seemal Jelani25

Reaction with sodium The reaction is similar to the reaction of alkali metals with water, but less vigorous. 5/12/2015Dr Seemal Jelani26

Esterification Catalyst: concentrated H 2 SO 4 (dehydrating agent - it removes water causing the equilibrium to move to the right and increases the yield Conditions:reflux 5/12/2015Dr Seemal Jelani27

Uses of estersEsters are fairly unreactive but that doesn’t make them useless Used as flavourings Naming estersNamed from the alcohol and carboxylic acid which made them... CH 3 OH + CH 3 COOH CH 3 COOCH 3 + H 2 O from ethanoic acid CH 3 COOCH 3 from methanol METHYL ETHANOATE Esters Ethanoate Methyl Methyl Ethanoate 5/12/2015Dr Seemal Jelani28