6.1.3 Carboxylic Acids and Esters Flashcards
what is a carboxylic acid
- contains the carboxyl functional group
- carbonyl (C=O) and hydroxyl (OH) functional group
- COOH
what are carboxylic acids often used for
- useful on their own
- or as starting materials for other compounds
- e.g. aspirin is made from salicylic acid
how do you name carboxylic acids
- the carboxyl group is indicated via the -oic acid suffix
- always placed on carbon 1
how would you name a carboxylic acid with a 4 carbon main chain and a methyl group coming off carbon 3
3-methylbutanoic acid
are carboxylic acids soluble, and why
- YES
- because both the C=O and O-H bonds are polar
- so can form hydrogen bonds with the water
- if drawing, remember dipoles
which carboxylic acids are soluble
- a carboxylic acid with up to 4 C atoms
what happens to the solubility as the number of carbon atoms in a carboxylic acid increases
- as the number of carbon atoms increases
- the solubility decreases
- as the non-polar carbon chain has a grater effect on the overall polarity of the molecule
- when comparing, always refer to the RATIO of carbons against COOH group
what is special about dicarboxylic acids and solubility
- have 2 polar carboxyl groups COOH to form hydrogen bonds
- so are usually solid at room temperature
- but readily dissolve
what type of acids are carboxylic acids
weak acids
- so only partially dissociate and release H+ ion
- e.g. HCOOH(aq) ⇌ H+(aq) + HCOO-(aq)
what is the basic way in which carboxylic acids act in acid reactions
- undergo redox reactions with metals
- and neutralisation reactions with bases, e.g. alkalis, metal oxides and carbonates
- FORM CARBOXYLATE SALTS
show how the carboxyl group forms a carboxylate ion
R-COOH → R-COO-
- carboxylate is used to name the ions formed
how do carboxylic acids react with metals
- in an aqueous solution
- forming hydrogen gas and a carboxylate salt
what would you be able to observe when a carboxylic acid reacts with a metal
- metal disappears
- effervescence as hydrogen gas evolves
what is important to remember when constructing equations to show the redox and neutralisation of carboxylic acids
- need to balance out the transfer of protons
- e.g. the monoprotic carboxylic acid and the base, whether monoprotic too or diprotic
how would you show the equation between propanoic acid and magnesium
2CH3CH2COOH(aq) + Mg(s) → (CH3CH2COO-)2Mg2+(aq) + H2
- as propanoic acid is monoprotic
- and Mg is diprotic (2+)
- so need to balance out the charges
how do carboxylic acids react with metal oxides
carboxylic acid + metal oxide → salt + water
what is the equation for ethanoic acid reacting with calcium oxide
2CH3COOH(aq) + CaO → (CH3COO-)2Ca2+(aq) → H2O
how do carboxylic acids react with alkalis
carboxylic acid + alkali → salt + water
- you may not see any reaction taking place at all, as 2 solutions are reacting to form an aqueous salt
how would you show ethanoic acid reacting with sodium hydroxide
CH3COOH(aq) + NaOH(aq) → CH3COO-Na+(aq) + H2O (l)
- ionically, is the neutralisation equation:
- H+ + OH- → H2O
how do carboxylic acids react with carbonates
carboxylic acid + carbonate → salt + water + carbon dioxide
- if the carboxylic acid is in excess, you should see any solid carbonate fully disappear
equation for ethanoic acid and sodium carbonate
2CH3COOH(aq) + Na2CO3(aq) → 2CH3COO-Na+ + H2O + CO2
how can you test for the carboxyl group
- can test via the neutralisation of carboxylic acids by carbonates
- as they are the only common organic compound acidic enough to react with carbonates
- especially useful when distinguishing between phenols
- as they aren’t acidic enough to react
what is a derivative of carboxylic acid
a compound that can be hydrolysed to form the parent carboxylic acid
what is the common series of atoms present in all derivatives of carboxylic acids
- the ACYL GROUP
- made of R-C=O (and then another line coming off the carbon
what are the 4 derivatives of carboxylic acids and what group is present coming off the 4th carbon bond
1) esters: OR (COO)
2) acyl chlorides Cl (COCl)
3) acid anhydrides (RCOO)
4) amides CONH2 (NH2)
what are esters
contain the functional group COO
- where C=O and C-O
- sweet smelling liquids
how are esters named
- named after their parent carboxylic acid they’re derived from
1) remove the -oic acid suffix from the parent carboxylic acid
2) replace suffix with -oate
3) the alkyl chain attached to the O coming off the COO group is used as the first word
how could you name CH3COOCH3
- methyl ethanoate
- ETHANoate off the ethanoic acid
- METHyl off the CH3 at the end
what are acyl chlorides
contain COCl
- where C=O and C-Cl
how are acyl chlorides named
- named after the parent carboxylic acid from which they are derived
1) remove the -oic acid off the parent acid
2) replace with -oyl chloride
how would you name CH3CH2COCl
propanoyl chloride
- PROPANoyl off the carboxylic acid
- chloride from the Cl
what are acid anhydrides
- formed via the removal of water from 2 carboxylic acid molecules
- the 2 OH groups combine, releasing water and leaving a O in the middle to join the 2 C=O
how do you name acid anhydrides
- whichever carboxylic acid has been combined with itself
- use as the prefix
- remove the acid from the end and replace with anhydride
what is the esterification equation
alcohol + carboxylic acid → ester (+ water)
what is esterification overview
- an alcohol is warmed with a carboxylic acid with a small amount of sulfuric acid acting as a catalyst
how does propanoic acid react with ethanol
CH3CH2COOH + CH3CH2OH → CH3CH2COOCH2CH3 + H2O
- propanoic acid + ethanol → ethyl propanoate + water
how do you make esters in a lab
1) add equal volumes (2cm3) of your carboxylic acid and alcohol to a boiling tube
2) add a few drops of sulfuric acid
3) place the beaker in hot water at 80 degrees C and leave for 5 minutes
4) pour contents into beaker containing sodium carbonate (aq) and you should see oily drops of ester in the mixture as well as being able to distinguish the sweet smell
- you add Na2CO3(aq) to act as a weak base neutralise any left over carboxylic acid left in the mixture, removing the smell of it so ester is easier to detect
what is hydrolysis
the chemical breakdown of a compound in the presence of water / in an aqueous solution
with what can esters be hydrolysed
- either an acid
- or alkali
what is acid hydrolysis of esters
- the opposite of esterification
- ester + water → carboxylic acid + alcohol
- the H+ can be given to a species, but none present as both the Os have Hs on them, so no specific product
how is the acid hydrolysis of esters carried out
1) the ester is heated under reflux with dilute aqueous acid
2) the ester is broken down by water, with acid acting as a catalyst
3) produced carboxylic acid and alcohol
- OH of water goes to the methyl chain attached to the C-O’s O and the O goes to the O of the C-O
write equation for the acid hydrolysis of methyl-2-hydroxybenzoate
OH⌬COOCH3 + H2O → OH⌬COOH + CH3OH
- forming 2-hydroxybenzoic acid and methanol
what is alkaline hydrolysis of esters
- known as saponification
- is irreversible
- ester is heated under reflux with aqueous hydroxide ions to form a carboxylate salt and alcohol
- the OH- ion needs to gain a H+ in order to form water, and can gain this from the H present in the carboxylic acids COOH
how would methyl ethanoate react under alkali hydrolysis
H3C-C-OO-CH3 + OH-(aq) → H3C-C-OO- + CH3OH
- forms an ethanoate ion and methanol
- for a specific alkali used, would form that carboxylate salt
how would you prepare acyl chlorides
- prepared from the parent carboxylic acid by a reaction with thionyl chloride SOCl2
- does also form SO2 and HCl, but these get evolved as gases, leaving just the acyl chloride behind
- MUST BE IN A FUME CUPBOARD, as forms harmful products
how can you form propionyl chloride
- reaction of propanoic acid with thionyl chloride
- e.g. CH3CH2COOH + SOCl2 → CH3CH2COCl + SO (g) + HCl(g)
why are acyl chlorides useful reactants in organic synthesis
- they are very reactive
- and can be easily converted into carboxylic acid derivatives, such a esters and amides, both with good yields
how do acyl chlorides react
- react with nucleophiles
- via losing the chloride ion
- but still retain the C=O bond
how do acyl chlorides react with alcohols
form esters (and HCl as a product)
- e.g. ethanoyl chloride + propan-1-ol → propyl ethanoate
- e.g. H3C-COCl + CH3CH2CH2OH → CH3COOCH2CH2CH3 + HCl
how do acyl chlorides react with phenols
- form esters
- carboxylic acids alone aren’t reactive enough to react with phenols
- but acyl chlorides, and acid anhydrides are
- as they are much more reactive
- so form phenyl esters WITH NO CATALYST NEEDED
how could I form phenyl ethanoate using an acyl chloride
- ethanoyl chloride + phenol →phenyl ethanoate + HCl
- H3C-COCl + HO-⌬ → H3C-COO-⌬ +HCl
how do acyl chlorides react with water
form carboxylic acids
- via a violent reaction taking place
- produces dense, steamy hydrogen chloride fumes
how could I form ethanoic acid from an acyl chloride
- ethanoyl chloride + water → ethanoic acid + HCl
- H3C-COCl + H2O → H3C-COOH + HCl
how do acyl chlorides react with ammonia and amines
- form amides O=C-N
how do ammonia and amines act when reacting with acyl chlorides
- act as nucleophiles
- as can donate the lone pair of electrons on the :N atom to an electron deficient species
what is the reaction between acyl chlorides and ammonia
- form primary amides
- primary as: the nitrogen is attached to ONE carbon atom (CNH2)
what is the reaction between ethanoyl chloride and ammonia
ethanoyl chloride + ammonia → ethanamide + ammonium chloride
- H3C-COCl + 2NH3 →H3C-CONH2 + NH4Cl
how do primary amines react with acyl chlorides
- react in the same way, forming a secondary amide
- where the nitrogen atom is attached to 2 carbons
how does ethanoyl chloride react with methylamine
ethanoyl chloride + methylamine → N-methylethanamide + methylammonium chloride
- H3C-COCl + 2CH3NH2 → H3C-CO-NH-CH3 + CH3NH3+Cl-
how do acid anhydride react
- in a similar way to acyl chlorides with alcohols, phenols, ammonia and amides
- but are LESS reactive than acyl chlorides
why might you choose acid anhydride in lab work rather than acyl chlorides
- where acyl chloride might be too reactive
how would ethanoic anhydride react with phenol
forms phenylethanoate + ethanoic acid
