4.5 carboxylic acids and their derivatives Flashcards
compare the acidity if carboxylic acids, alcohols, phenols and water
c/a > phenols > water > alcohols
<————————— increasing acidity
- carboxylic acids are acidic. they are weak acids
- phenols are also weak acids as they can lose a proton to form a _____
phenoxide
what is an acid?
a proton donor
why arent alcohols acidic?
they cant delocalise electrons and so are unstable
why are carboxylic acids more acidic than phenols?
- c/a have more delocalisation as O is electronegative
- so more stable and so more acidic
carboxylic acids will react with:
- weaker bases: sodium hydrogencarbonate and sodium carbonate to form a salt, carbon dioxide and water
- strong bases: sodium hydroxide to form a salt and water
phenols will react with:
- strong bases: sodium hydroxide to form the phenoxide salt and water
- BUT NOT with weaker bases like sodium hydrogencarbonate (as its a weaker acid than c/a)
water and alcohols will react with:
- nothing
- they wont react with weak or strong bases
phenol + Na2CO3 —>
no reaction
primary alcohols can be fully oxidised to carboxylic acids using ______?
acidified potassium dichromate under reflux
aldehydes can also be oxidised to carboxylic acids using _____
acidified potassium dichromate under reflux
what is the colour change for the oxidation of alcohols to carboxylic acids?
orange to green
what is produced when carboxylic acids are reduced using LiAlH4?
primary alcohol + water
how are aromatic carboxylic acids formed?
- by oxidation of a methyl side chain which is bonded to a benzene ring
- with the oxidising agent being a solution of potassium manganate (VIII) in an alkaline solution of sodium hydroxide under reflux (OH-/KMnO4)
- and then followed by adding dilute sulfuric acid
what is an aromatic carboxylic acid?
a benzene ring that had a carboxyl group, COOH directly bonded to it
what is the colour change for the formation of an aromatic carboxylic?
- the purple colour of potassium manganate (VIII) is eventually replaced by a dark brown precipitate of manganese (VI) oxide
- purple —> dark brown precipitate
why is sulfuric acid needed to be added in the second step of forming an aromatic carboxylic acid?
to protonate the salt
propylbenzene — 1. alkaline potassium manganate (VII) reflux 2. dilute sulfuric acid —>
- benzoic acid
- ANY alkyl group is oxidised back to a COOH group on the ring under these conditions
what happens in the decarboxylation of carboxylic acids?
- the -COOH or -COONa group is removed and replaced with a hydrogen atom
what is the decarboxylating agent in the decarboxylation of carboxylic acids?
- decarboxylating agent = sodalime
what is sodalime a mixture of?
- sodium hydroxide
- calcium oxide
- calcium hydroxide
how is sodalime written in equations?
- as if the carboxylic acid was simply reacting with sodium hydroxide
what does the decarboxylation of carboxylic acids form?
C/A —> alkene + CO2
why is the decarboxylation of carboxylic acids important?
it shortens the carbon chain
if propanedioic acid (COOHCH2COOH) is decarboxylated using sodalime, what is formed?
EITHER:
- methane
- ethanoic acid
how are esters made from carboxylic acids?
- any carboxylic acid reacts with an alcohol to give a sweet-smelling ester (+ water)
what does the formation of esters from carboxylic acids and alcohols require?
- a concentrated sulfuric acid catalyst
- heated under reflux
in the formation of esters from carboxylic acids and alcohols, what can be done to favour the production of esters?
- water can be removed as ester is formed
- this is called esterification
in the formation of esters from carboxylic acids and alcohols, what can be done to favour the production of carboxylic acids?
excess water can be added
- this reaction is called hydrolysis
is the formation of esters from carboxylic acids and alcohols reversible?
yes
(so yields can be lower)
carboxylic acid + alcohol —-esterification—-> ester
carboxylic acid + alcohol <—- hydrolysis—- ester
what reagent is usually used in the reaction from carboxylic acids to acid chlorides?
- thionyl chloride, SOCl2
what reagent can be used in the reaction from carboxylic acids to acid chlorides? why is it not as preferred?
- PCl3 or PCl5
- but the products are more difficult to separate from the end reaction mixture
compare the hydrolysis of acyl chlorides and esters:
- esters are more difficult to hydrolyse than acid chlorides
- hydrolysis of esters gives back the alcohol and carboxylic acid used to make the ester
- hydrolysis of an acid chlorides yields a carboxylic acid and ‘fuming’ hydrogen chloride gas
- the hydrolysis of acid chlorides is much more rapid than the hydrolysis of esters
- acid chlorides will react vigorously with cold water
are esters or acid chlorides more difficult to hydrolyse?
esters
the hydrolysis of esters does what?
gives back the alcohol and carboxylic acid used to make the ester
the hydrolysis of an acid chlorides does what?
- yields a carboxylic acid and ‘fuming’ hydrogen chloride gas
how do you get from an acid chlorides to a carboxylic acid?
- add water
- (hydrolysis)
- acid chloride + water —> c/a + HCl (g)
how do you get from an acid chlorides to an ester?
acid chloride + alcohol —> ester + HCl(g)
how do you get from an acid chlorides to an amide?
acid chloride + NH3 —> amide + HCl (g)
what is an amide?
a group that had a nitrogen that is directly bonded to a carbonyl group
R−C(=O)−NR′R″
- the R’ and R’’ groups can be carbon chains or hydrogen atoms
in R−C(=O)−NR′R″, if R’ and R’’ are hydrogen atoms, what is the functional group?
an amide
in R−C(=O)−NR′R″, if R’ and R’’ are carbon chains, what is the functional group?
an N-substituted amide
how do you name amides?
- end in amide
e.g ethanamide or propanamide
how do you name N substituted amides?
- name the carbons bonded to the N first (then write an N infront of it)
- then name the bit that the carbonyl group is attached to
e.g N-methyl ethanamide or N-propylpropanamide
- or N,N-dimethylethanamide or N-ethyl-N-methylethanamide
what is the reaction of carboxylic acids to amides?
- a 2 step process
- add ammonia, NH3
- this yields the ammonium salt of the carboxylic acids to
- need to then heat strongly to dehydrate the salt to make the amide
what is the reaction from amides to nitriles?
- dehydration
- dehydrating agent = phosphorus (V) oxide, P4O10/P2O5
- also requires heat
amide + P4O10 —> nitrile + water
what is the reaction for the formation of nitriles from halogenoalkanes?
- potassium cyanide, KCN dissolved in ethanol
- nucleophilic substitution
halogenoalkane + KCN in ethanol —> nitrile
(DONT GET THIS MIXED UP WITH HYDROGEN CYANIDE (HCN) REACTING WITH ALDEHYDES AND KETONES)
why is the reaction for the formation of nitriles from halogenoalkanes important?
as it lengthens the carbon chain
what is the mechanism for the formation of nitriles from halogenoalkanes?
nucleophilic substitution
the hydrolysis of nitriles and amides always gives what?
the corresponding carboxylic acids
in the hydrolysis of nitriles and amides, if acid hydrolysis is used, what is the reagent?
dilute H2SO4
(under reflux)
in the hydrolysis of nitriles and amides, if alkaline hydrolysis is used, what is the reagent?
dilute NaOH
under reflux
in the hydrolysis of nitriles and amides, what is a disadvantage of using alkaline hydrolysis?
- the sodium carboxylate salt formed needs to be acidified to get the parent carboxylic acid
- (need to add acid anyway to protonate)
- sometimes has a reduced yield as it’s a 2 step process
what is produced when you reduce a nitrile?
- an amine
what type of reaction is it for forming an amine from a nitrile?
reduction
what is the reaction for the formation of an amine from a nitrile?
nitrile + LiAlH4 in dry ether solution —> amide
name the type of reaction carried out when an alcohol reacts to form a carboxylic acid
oxidation
what is the intermediate product formed during the oxidation of an alcohol to form a carboxylic acid?
an aldehyde
this then undergoes further oxidation to form a carboxylic acid
what reaction conditions are acquired to ensure complete oxidation of the alcohol to the carboxylic acid?
- excess oxidising agent (acidified potassium dichromate (VI)) needs to be added to the alcohol and it must be heated under reflux
what type of alcohol will produce carboxylic acids when oxidised?
primary alcohols
what is the reducing agent used to reduce carboxylic acid to alcohols?
LiAlH4
(NaBH4 not reactive enough to reduce c/a)
what reagents are required to oxidise methylbenzene to benzoic acid?
- alkaline potassium manganate (VIII) is first added to the methylbenzene
- once a dark brown ppt forms, the mixture is acidified with dilute sulfuric acid
methylbenzene forms benzoic acid under oxidation. what does propylbenzene form when it undergoes oxidation?
benzoic acid
- regardless of the length of the side chain, all side chains are oxidised to a -COOH group
what is decarboxylation?
- the process by which the -COOH group of a c/a or -COO-NA+ group of a carboxylate salt is removed from the molecule and replaced with a hydrogen atom
what is a common reagent used for decarboxylation?
sodalime
what is the chemical equation for the reaction between sodium ethanoate and sodalime?
CH3COO-Na+ + NaOH —> CH4 + Na2CO3
whats the chemical equation for the reaction between benzoic acid and sodalime?
C6H5COOH + 2NaOH —> C6H6 + Na2CO3 + H2O
what is formed when an alcohol reacts with a carboxylic acid?
an ester
name the ester formed in the reaction between butanoic acid and propanol
propyl butanoate
what are the identifying properties of esters?
- sweet smelling
- often used in flavourings and perfumes
- have a low boiling point
- and make good solvents for other polar molecules
what is used as a catalyst in esterification reactions?
concentrated sulfuric acid
why is hydrogen chloride sometimes a preferred catalyst for esterification ?
hydrogen chloride gives a better yield since no alkene side products are formed
give the three possible reagents which can be used to produce an acyl chloride from a carboxylic acid
- phosphorus (V) chloride, PCl5
- phosphorus (III) chloride, PCl3
- thionyl chloride, SOCl2
what is the chemical equation for the reaction between ethanoic acid and phosphorus (V) chloride?
CH3COOH + PCl5 —> CH3COCl + POCl3 + HCl
what is the chemical equation for the reaction between propanoic acid and phosphorus (III) chloride?
3CH3CH2COOH + PCl3 —> 3CH3CH2COCl + H3PO3
what is the chemical equation for the reaction between ethanoic acid and thionyl chloride?
CH3COOH + SOCl2 —> CH3COCl + SO2 + HCl
why is SOCl2 the preferred reagent when making acid chlorides?
- in the reaction with SOCl2, the byproducts are gaseous so it’s easier to obtain the acid chloride
- isolation of the acid chloride is more difficult when using PCl3 or PCl5
name the type of reaction in which esters and acid chlorides can react to form carboxylic acids?
hydrolysis - a reaction in which a substance is split up by water
what is produced when a halogenoalkane reacts with ethanolic potassium cyanide?
a nitrile
how do the reactants and products of base hydrolysis of nitriles compare to those of acid hydrolysis of nitriles?
- acid:
• dilute H2SO4
• carboxylic acid and ammonium sulfate - alkaline:
• dilute NaOH
• sodium carboxylate salt and ammonia
what is the reducing agent used in the reduction of nitriles to amines?
LiAlH4
what is the chemical equation for the reduction of propanenitrile to propylamine?
CH3CH2CN + 4[H] —> CH3CH2CH2NH2
