carboxylic acids + derivatives Flashcards
(33 cards)
are ca weak/strong, what are they strong enough to displace?
The carboxylic acid are only weak acids in water and only slightly dissociate, but they are strong enough to displace carbon dioxide from carbonates.
CH3CO2H(aq) <-> CH3CO2-(aq)+ H+(aq)
Solubility in water of Case
The smaller carboxylic (up to C4) acids dissolve in water in all proportions but after this the solubility rapidly reduces. They dissolve becausetheycanhydrogenbondto the water molecules.
what makes dissociation of CAs more likely
the fact the CA salts are stabilised by delocalisation - The delocalised ion has equal C-O bond lengths. If delocalisation did not occur, the C=O bond would be shorter than the C-O bond. The pi charge cloud has delocalised and spread out. The delocalisation makes the ion more stable and therefore more likely to form.
why is Propanoic acid less acidic than ethanoic acid
Alkyl groups electron releasing
Increasing chain length pushes electron density on to the COO- ion, making it more negative and less stable. This make the acid less strong.
Chloroethanoic acid is more acidic than ethanoic acid why
Chlorine electron withdrawing
Electronegative chlorine atoms withdraw- electron density from the COO ion, making it less negative and more stable. This make the acid more strong.
CA + metal
acid + metal (Na) salt + hydrogen 2CH3CO2H + 2Na 2CH3CO2-Na+ + H2
CA + alkali
CH3CO2H + NaOHCH3CO2-Na+ + H2O
CA + carbonate
acid + carbonate (Na2CO3) salt + water + CO2
2CH3CO2H + Na2CO3 2CH3CO2-Na+ + H2O + CO2
functional grp test for CAs
The effervescence caused by production of CO2 with carboxylic acids with solid Na2CO3 or aqueous NaHCO3 can be used as a functional group test for carboxylic acids
why can methanol acid be oxidised, what does it oxidize to form
its structure has effectively an aldehyde group.
oxidises to form carbonic acid (H2 CO3 ) which can decompose to give CO2
esterification how
Carboxylic acids react with alcohols, in the presence of a strong acid catalyst, to form esters and water.
The reaction is reversible. The reactionisquiteslowandneeds heating under reflux, (often for several hours or days). Low yields (50%ish)areachieved.Anacid catalyst (H2SO4) is needed.
uses of esters
Esters are sweet smelling compounds that can be used in perfumes and flavourings.
Esters can be used as solvents for polar organic substances- Ethyl ethanoate is used as a solvent in glues and printing inks.
Esters can be used as plasticisers for polymers.
Hydrolysis of esters 2 ways
either heating with acid or with sodium hydroxide.
hydrolysis of ester w acid
reagents: dilute acid (HCl) conditions: heat under reflux
CH3CH2CO2CH2CH3 + H2O ethyl propanoate
H+
CH3CH2CO2H + CH3CH2OH
This reaction is reversible and does not give a good yield of the products.
Hydrolysis of esters with sodium hydroxide why is this reaction not reversible
reagents: dilute sodium hydroxide conditions: heat under reflux
- This reaction goes to completion. Using excess sodium hydroxide will ensure the ester is completely hydrolysed.
- The carboxylic acid salt product is the anion of the carboxylic acid.
The anion is resistant to attack by weak nucleophiles such as alcohols, so the reaction is not reversible.
CH3CH2CO2CH3 + NaOH -> CH3CH2CO2- Na+ + CH3OH
Addition of a strong acid such as hydrochloric acid to the carboxylic acid salt will convert the salt to the carboxylic acid form. CH3CH2CO2- Na+ + HCl -> CH3CH2CO2H + NaCl
Hydrolysis of ethyl benzoate method
The liquid ethyl benzoate can be hydrolysed by sodium hydroxide by heating under reflux for 30 minutes.
After the reaction is complete allow the mixture to cool to room temperature and add hydrochloric acid. A precipitate of benzoic acid will be produced that can be filtered off using suction filtration.
C6H5COONa + HClC6H5COOH + NaCl
The benzoic acid can then be purified with the steps outlined in practical guide AQA required practical 10 purification of an organic solid.
why is sodium benzoate soluble in water but benzoic acid not
Sodium benzoate is soluble in water because it is ionic. Benzoic acid, however, is insoluble. This is because even though the polar COOH group can form hydrogen bonds, the benzene ring is non-polar. In organic compounds there are often polar parts and non-polar parts. The solubility in water of a compound will controlled by whether the polar or non polar part is of greater importance.
what are Fats and soaps
esters of glycerol and long chain carboxylic acids (fatty acids)
Vegetable oils and animal fats can be hydrolysed to give
soap, glycerol and long chain carboxylic (fatty) acids
Glycerol uses and why
forms hydrogen bonds very easily and is readily soluble in water. It is used in cosmetics, food and in glues.
Soap use + why
The polar CO2- end is hydrophilic and mixes with water. The long non-polar hydrocarbon chain is hydrophobic and mixes with grease. So this allows the grease and water to mix and be washed away.
Biodiesel?
a mixture of methyl esters of long chain carboxylic acids
Vegetable oils can be converted into biodiesel by
reaction with methanol in the presence of a (strong alkali) catalyst
acyl chlorides + acid anhydrides reactivity comp to CAs + esters
-much more reactive than carboxylic acids
- The Cl and –OCOCH3 groups are classed as good leaving groups (to do with less effective delocalisation.) This makes acyl chlorides and acid anhydrides much more reactive than carboxylic acids and esters
