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AlcoholsButan - 1, 4 - diolButan- 1- olPropan- 2- olPropan- 1- ol
These all have the formula C4H9OHbutan-1-olbutan-2-ol2-methylpropan-1-ol2-methylpropan-2-ol
Bond angles in alcohol groups
Solubility in waterThe alcohol groups form hydrogen bonding which makes the short chain molecules soluble in water.
The solubility in water decreases as the chain length increases.
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.
Boiling Points of AlcoholsIncreases with molecular size due to increased instantaneous dipolesAlcohols have higher boiling points than similar molecular mass alkanesThis is due to the added presence of inter-molecular hydrogen bonding. More energy is required to separate the molecules Mr bp / CpropaneC3H8 44 -42just instantaneous dipolesethanolC2H5OH 46 +78 instantaneous dipoles + hydrogen bonding
Boiling point is higher for straight chain isomers. bp / Cbutan-1-ol CH3CH2CH2CH2OH118butan-2-ol CH3CH2CH(OH)CH31002-methylbutan-2-ol (CH3)3COH 83
CLASSIFICATION OF ALCOHOLSAliphatic general formula CnH2n+1OH - provided there are no rings the OH replaces an H in a basic hydrocarbon skeleton
Structuraldifferences alcohols are classified according to the environment of the OH group chemical behaviour, eg oxidation, often depends on the structural type PRIMARY 1 SECONDARY 2 TERTIARY 3NB. Aliphatic - straight chain molecule (not a ring / cyclic)
OXIDATION OF PRIMARY ALCOHOLSPrimary 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
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 didnt distil off it would be oxidised to the equivalent carboxylic acid to oxidise an alcohol straight to the acid, reflux the mixture
compound formulaintermolecular bondingboiling point ETHANOL C2H5OHHYDROGEN BONDING 78C ETHANAL CH3CHODIPOLE-DIPOLE 23C ETHANOIC ACID CH3COOHHYDROGEN BONDING 118C
Oxidising a primary alcohol to an aldehydeFull oxidation is not wanted:use dilute acid and less dichromate. The reaction mixture is heated gently, ethanal vapourises (21C) as soon as it is formed and distils over. This stops it being oxidised further to ethanoic acid.
Apparatus for the oxidation of ethanol to ethanoic acid
Oxidising a primary alcohol to a carboxylic acidrefluxDistil to separate
Oxidising a secondary alcohol to a ketone
Oxidation of alcoholsPrimary 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.
Oxidation of alcoholsPrimary alcoholstertiary alcoholSecondary alcoholaldehydesCarboxylic acidDont oxidiseKetones
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 12 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.
Distinguishing alcohols - Lucas testPrimary alcohol - remain unchangedtertiary alcohol - turns cloudy immediatelySecondary alcohol - will turn cloudy but takes a bit of timeLucas reagent = conc. HCl and ZnCl2
Tertiary alcohols turn cloudy immediately.
Once heated, the secondary alcohol quickly turned cloudy.
The primary alcohol tube is unchanged.
Formation of ethanol by fermentationConditionsyeastwarm, but no higher than 37C (optimum temp. for yeast)
AdvantagesLOW ENERGY PROCESSUSES RENEWABLE RESOURCES - PLANT MATERIALSIMPLE EQUIPMENT
DisadvantagesSLOWPRODUCES IMPURE ETHANOL - will need distilling to purifyBATCH PROCESS
Formation of haloalkane Ethanol and PCl5
C2H5OH(l) + PCl5(s) C2H5Cl(g) + POCl3(l) + HCl(g)fumessolidEthanol and SOCl2
C2H5OH(l) + SOCl2(l) C2H5Cl(g) + SO2(g) + HCl(g)
Formation of ethanol from ethene
AdvantagesFASTPURE ETHANOL PRODUCEDCONTINUOUS PROCESS
DisadvantagesHIGH ENERGY PROCESSEXPENSIVE PLANT REQUIREDUSES NON-RENEWABLE FOSSIL FUELS TO MAKE ETHENE
Uses of ethanolALCOHOLIC DRINKSSOLVENT - industrial alcohol / methylated spiritsFUEL - petrol substitute in countries with limited oil reserves
Dehydration of alcoholsReagent: concentrated sulphuric acidor passing the alcohol over aluminium oxide
Reaction with sodiumThe reaction is similar to the reaction of alkali metals with water, but less vigorous.
EsterificationCatalyst: concentrated H2SO4 (dehydrating agent - it removes water causing the equilibrium to move to the right and increases the yieldConditions:reflux
Uses of estersEsters are fairly unreactive but that doesnt make them uselessUsed as flavourings
Naming estersNamed from the alcohol and carboxylic acid which made them...
CH3OH + CH3COOH CH3COOCH3 + H2O
from ethanoic acid CH3COOCH3 from methanol METHYL ETHANOATEEstersEthanoateMethylMethyl Ethanoate
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