26.2) Carboxylic acids and esters
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state the structure of carboxylic acids and how are they named
have functional group -COOH - they are named _____anoic acid
state what carboxylic acids are and what this means when aqueous, give an example equation
they are WEAK acids - proton donor - so will PARTIALLY dissociate in water - this forms H+ and a carboxylate ion e.g. CH3CH2COOH ⇌ CH3CH3COO- + H+ - this forms H+ and propanoate ion - equilibrium lies far left
what does carboxylic acids being acid mean, give an example
can react with carbonates e.g. 2CH3COOH(aq) + Na2CO3(s) 🡢 2CH3COONa(aq) + CO2(g) + H2O(l) - this forms CO2 and so there will be effervescence/bubbles of gas • CH3COONa can also be written as CH3COO-Na+ • this is the SALT sodium ethanoate
describe structure of esters, what they are synthesised from, and how to name them
have -COO- functional group - made from a carboxylic acid reacting with an alcohol - named alkyl ____anoate - alkyl comes from alcohol group - _____anoate comes from CA group e.g. CH3COOCH2CH2CH3 is propyl ethanoate
give reagents and conditions for synthesis of ester CH3COOCH2CH3, include an equation, name this product
• using ethanoic acid and ethanol • in presence of strong acid catalyst - CONC. H2SO4 • heated under reflux CH3COOH + CH3CH2OH ⇌ CH3COOCH2CH3 + H2O - this is ethyl ethanoate
give 4 uses of esters, justifying each
1 - perfumes 2 - food/drink flavourings - BOTH as esters have sweet smells 3 - solvents e.g. in glue, printing inks - as esters are polar - so polar molecules can dissolve - also low b.p/volatile so evaporate easily 4 - plasticisers - added to plastics in polymerisation - make plastics more flexible - BUT - will escape so plastic becomes brittle/stiff
state how esters are hydrolysed
adding water to split back into an alcohol and other product 2 types: 1 - acid hydrolysis 2 - base hydrolysis
describe acid hydrolysis, include reagents and conditions, give an example equation of hydrolysing CH3COOCH3
• uses a dilute acid catalyst, heat under reflux • produces an alcohol and carboxylic acid e.g. CH3COOCH3 + H2O ⇌ CH3COOH + CH3OH - methyl ethanoate + water ⇌ ethanoic acid + methanol
describe base hydrolysis, include reagents and conditions, give an example equation of hydrolysing CH3COOCH2CH3
• heat under reflux with a dilute base e.g. NaOH • the base will take part in the reaction • this produces and alcohol and carboxylate ion/salt e.g. CH3COOCH2CH3 + OH- 🡢 CH3COO- + CH3CH2OH - the carboxylate ion can then react with Na+ to form sodium ethanoate • ethyl ethanoate + sodium hydroxide 🡢 sodium ethanoate + ethanol
give 2 properties of carboxylic acids and explain why
1 - high melting point - have hydrogen bonding between molecules - so takes more heat energy to overcome 2 - soluble in water - can form hydrogen bonds with water
what are vegetable oils and animal fats, and what are they made from
they are ESTERS - made from fatty acids - long chain carboxylic acids - and glycerol - propane-1,2,3-triol • they are known as triglycerides
compare melting point of fats and oils
1 - fats - made up of SATURATED fatty acids (C-C) - so hydrocarbon chains can pack closely together - so stronger and more vdW forces between molecules/chains - so take more heat energy to overcome - so higher melting point = solid at room temp. 2 - oils - made up of UNSATURATED (C=C) fatty acids - so cannot pack as closely together due to kinks in the chain - so less vdW forces - takes LESS heat energy to overcome - lower melting point = liquid at room temp
describe hydrolysis of fats an oils, include products and write an example equation of hydrolysis (CH2OCOR)(CHOCOR)(CH2OCOR)
heated with NaOH in BASE hydrolysis - this forms glycerol and SOAP - soap is a salt of a long chain carboxylic acid e.g. (CH2OCOR)(CHOCOR)(CH2OCOR) + 3NaOH 🡢 CH2(OH)CH(OH)CH2(OH) + 3RCOO-Na+ - this is a sodium salt = SOAP
describe how biodiesel is made, include an example equation using (CH2OCOR)(CHOCOR)(CH2OCOR)
• mixture of methyl esters • made from reacting vegetable oils with methanol • with a KOH catalyst e.g. (CH2OCOR)(CHOCOR)(CH2OCOR) + 3CH3OH 🡢 CH2(OH)CH(OH)CH2(OH) + 3 CH3OOCR • triester + methanol 🡢 glycerol + methyl esters = biodiesel
describe the structure of acyl chlorides and explain how they are named
have functional group -OCl - they have a Cl instead of an OH group in a carboxylic acid - they are named ____oyl chloride e.g. ethanoyl chloride
describe the structure of acid anhydrides and how they are named, give the structural formula of propanoic anhydride
• 2 identical carboxylic acid molecules joined together • named ____oic anhydride e.g. (CH3CH2CO)2O is propanoic anhydride
describe the structure of amides, what can also be formed, and how they are named
AMIDES - have functional group CONH2 - they are named ____amide e.g. CH3CONH2 = ethanamide can also form N-substituted amides - when one H on the N is replaced by an R group - named N- _____________amide e.g. CH3CH2CON(CH3)H = N-methylpropanamide
state how acyl chlorides react with: 1) water 2) alcohols 3) ammonia 4) primary amines give equations for each 5) give observations seen for ALL reactions
1) nucleophilic addition elimination - forms a carboxylic acid and HCl - CH3COCl + H2O 🡢 CH3COOH + HCl 2) nucleophilic addition elimination - forms an ester and HCl - CH3COCl + CH3OH 🡢 CH3COOCH3 + HCl 3) nucleophilic addition elimination - forms an amide and HCl - CH3COCl + NH3 🡢 CH3CONH2 + HCl 4) nucleophilic addition elimination - forms an N-substituted amide and HCl - CH3COCl + N(CH3)H2 🡢 CH3CONH(CH3) + HCl 5) all are vigorous quick reactions, produce steamy fumes of HCl
give equations for the reaction of ethanoic anhydride with: 1) water 2) alcohol (methanol) 3) ammonia 4) primary amine (methylamine)
1) makes 2 carboxylic acids - (CH3CO)2O + H2O 🡢 2CH3COOH 2) makes ester and CA - (CH3CO)2O + CH3OH 🡢 CH3COOCH3 + CH3COOH 3) makes amide and CA - (CH3CO)2O + NH3 🡢 CH3CONH2 + CH3COOH 4) makes N-substituted amide and CA - (CH3CO)2O + CH3NH2 🡢 CH3CONH(CH3) + CH3COOH
explain why acid anhydrides are preferable over using acyl chlorides when making aspirin
• cheaper than acyl chlorides • safer + less corrosive • as it reacts more slowly/less vigorously • does not produce toxic fumes of HCl gas
required practical 10
give a method to prepare an organic solid, justify each stage
1) weigh mass of solid using a weighing boat and mass balance 2) add the solid into a conical flask - so swirling is easier 3) reweigh the weighing boat - so you know the exact mass of solid added 4) add ethanoic anhydride (not ethanoyl chloride) and conc. acid catalyst - as it is safer - the reaction is less vigorous - also no toxic HCl fumes produced - catalyst will speed up rate 5) warm solution in a water bath - as organic compounds flammable and will speed up reaction 6) add ice cold water - as this will cause the solid to crystallise and will have a higher yield 7) filter under reduced pressure with double filter paper - using buchner funnel 8) dry solid in an oven
give the method for purifying an organic solid by recrystallisation, include justifications of each stage
1) dissolve in the minimum volume of hot solvent - to get a saturated solution so crystals form on cooling - this is a higher yield - solvents needs to dissolve solid and impurities when hot but not when cold 2) hot filtration - so that any insoluble impurities are removed - NOT buchner - as this would cause substance to crystallise = lower yeild 3) cool and leave to crystallise - as yield is higher when cold 4) filter under reduced pressure - to remove soluble impurities from surface of crystals - leads to purer/drier solid 5) compress the crystals - so air passes through the crystals - not just around them 6) wash with ice cold water - to remove any soluble impurities 7) dry in an oven on double filter paper
describe how to test the purity of an organic solid, give 3 ways which show the sample is impure
1) put sample into a glass capillary tube 2) heat sample in a thiele tube with a thermometer measuring the temperature 3) heat slowly near the melting point - as this enables you to get an exact melting point of the solid 4) record the temperature when sample melts and compare this to a data book value IF sample is IMpure - melting point is lower - boiling point is higher - it will melt over a range of temperatures