4.5 carboxylic acids and their derivatives Flashcards
1
Q
compare the acidity if carboxylic acids, alcohols, phenols and water
A
c/a > phenols > water > alcohols
<————————— increasing acidity
2
Q
- carboxylic acids are acidic. they are weak acids
- phenols are also weak acids as they can lose a proton to form a _____
A
phenoxide
3
Q
what is an acid?
A
a proton donor
4
Q
why arent alcohols acidic?
A
they cant delocalise electrons and so are unstable
5
Q
why are carboxylic acids more acidic than phenols?
A
- c/a have more delocalisation as O is electronegative
- so more stable and so more acidic
6
Q
carboxylic acids will react with:
A
- 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
7
Q
phenols will react with:
A
- 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)
8
Q
water and alcohols will react with:
A
- nothing
- they wont react with weak or strong bases
9
Q
phenol + Na2CO3 —>
A
no reaction
10
Q
primary alcohols can be fully oxidised to carboxylic acids using ______?
A
acidified potassium dichromate under reflux
11
Q
aldehydes can also be oxidised to carboxylic acids using _____
A
acidified potassium dichromate under reflux
12
Q
what is the colour change for the oxidation of alcohols to carboxylic acids?
A
orange to green
13
Q
what is produced when carboxylic acids are reduced using LiAlH4?
A
primary alcohol + water
14
Q
how are aromatic carboxylic acids formed?
A
- 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
15
Q
what is an aromatic carboxylic acid?
A
a benzene ring that had a carboxyl group, COOH directly bonded to it
16
Q
what is the colour change for the formation of an aromatic carboxylic?
A
- the purple colour of potassium manganate (VIII) is eventually replaced by a dark brown precipitate of manganese (VI) oxide
- purple —> dark brown precipitate
17
Q
why is sulfuric acid needed to be added in the second step of forming an aromatic carboxylic acid?
A
to protonate the salt
18
Q
propylbenzene — 1. alkaline potassium manganate (VII) reflux 2. dilute sulfuric acid —>
A
- benzoic acid
- ANY alkyl group is oxidised back to a COOH group on the ring under these conditions
19
Q
what happens in the decarboxylation of carboxylic acids?
A
- the -COOH or -COONa group is removed and replaced with a hydrogen atom
20
Q
what is the decarboxylating agent in the decarboxylation of carboxylic acids?
A
- decarboxylating agent = sodalime
21
Q
what is sodalime a mixture of?
A
- sodium hydroxide
- calcium oxide
- calcium hydroxide
22
Q
how is sodalime written in equations?
A
- as if the carboxylic acid was simply reacting with sodium hydroxide
23
Q
what does the decarboxylation of carboxylic acids form?
A
C/A —> alkene + CO2
24
Q
why is the decarboxylation of carboxylic acids important?
A
it shortens the carbon chain
25
if propanedioic acid (COOHCH2COOH) is decarboxylated using sodalime, what is formed?
EITHER:
- methane
- ethanoic acid
26
how are esters made from carboxylic acids?
- any carboxylic acid reacts with an alcohol to give a sweet-smelling ester (+ water)
27
what does the formation of esters from carboxylic acids and alcohols require?
- a concentrated sulfuric acid catalyst
- heated under reflux
28
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
29
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
30
is the formation of esters from carboxylic acids and alcohols reversible?
yes
(so yields can be lower)
31
carboxylic acid + alcohol —-esterification—-> ester
carboxylic acid + alcohol <—- hydrolysis—- ester
32
what reagent is usually used in the reaction from carboxylic acids to acid chlorides?
- thionyl chloride, SOCl2
33
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
34
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
35
are esters or acid chlorides more difficult to hydrolyse?
esters
36
the hydrolysis of esters does what?
gives back the alcohol and carboxylic acid used to make the ester
37
the hydrolysis of an acid chlorides does what?
- yields a carboxylic acid and ‘fuming’ hydrogen chloride gas
38
how do you get from an acid chlorides to a carboxylic acid?
- add water
- (hydrolysis)
- acid chloride + water —> c/a + HCl (g)
39
how do you get from an acid chlorides to an ester?
acid chloride + alcohol —> ester + HCl(g)
40
how do you get from an acid chlorides to an amide?
acid chloride + NH3 —> amide + HCl (g)
41
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
42
in R−C(=O)−NR′R″, if R’ and R’’ are hydrogen atoms, what is the functional group?
an amide
43
in R−C(=O)−NR′R″, if R’ and R’’ are carbon chains, what is the functional group?
an N-substituted amide
44
how do you name amides?
- end in amide
e.g ethanamide or propanamide
45
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
46
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
47
what is the reaction from amides to nitriles?
- dehydration
- dehydrating agent = phosphorus (V) oxide, P4O10/P2O5
- also requires heat
amide + P4O10 —> nitrile + water
48
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)
49
why is the reaction for the formation of nitriles from halogenoalkanes important?
as it lengthens the carbon chain
50
what is the mechanism for the formation of nitriles from halogenoalkanes?
nucleophilic substitution
51
the hydrolysis of nitriles and amides always gives what?
the corresponding carboxylic acids
52
in the hydrolysis of nitriles and amides, if acid hydrolysis is used, what is the reagent?
dilute H2SO4
(under reflux)
53
in the hydrolysis of nitriles and amides, if alkaline hydrolysis is used, what is the reagent?
dilute NaOH
under reflux
54
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
55
what is produced when you reduce a nitrile?
- an amine
56
what type of reaction is it for forming an amine from a nitrile?
reduction
57
what is the reaction for the formation of an amine from a nitrile?
nitrile + LiAlH4 in dry ether solution —> amide
58
name the type of reaction carried out when an alcohol reacts to form a carboxylic acid
oxidation
59
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
60
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
61
what type of alcohol will produce carboxylic acids when oxidised?
primary alcohols
62
what is the reducing agent used to reduce carboxylic acid to alcohols?
LiAlH4
(NaBH4 not reactive enough to reduce c/a)
63
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
64
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
65
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
66
what is a common reagent used for decarboxylation?
sodalime
67
what is the chemical equation for the reaction between sodium ethanoate and sodalime?
CH3COO-Na+ + NaOH —> CH4 + Na2CO3
68
whats the chemical equation for the reaction between benzoic acid and sodalime?
C6H5COOH + 2NaOH —> C6H6 + Na2CO3 + H2O
69
what is formed when an alcohol reacts with a carboxylic acid?
an ester
70
name the ester formed in the reaction between butanoic acid and propanol
propyl butanoate
71
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
72
what is used as a catalyst in esterification reactions?
concentrated sulfuric acid
73
why is hydrogen chloride sometimes a preferred catalyst for esterification ?
hydrogen chloride gives a better yield since no alkene side products are formed
74
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
75
what is the chemical equation for the reaction between ethanoic acid and phosphorus (V) chloride?
CH3COOH + PCl5 —> CH3COCl + POCl3 + HCl
76
what is the chemical equation for the reaction between propanoic acid and phosphorus (III) chloride?
3CH3CH2COOH + PCl3 —> 3CH3CH2COCl + H3PO3
77
what is the chemical equation for the reaction between ethanoic acid and thionyl chloride?
CH3COOH + SOCl2 —> CH3COCl + SO2 + HCl
78
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
79
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
80
what is produced when a halogenoalkane reacts with ethanolic potassium cyanide?
a nitrile
81
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
82
what is the reducing agent used in the reduction of nitriles to amines?
LiAlH4
83
what is the chemical equation for the reduction of propanenitrile to propylamine?
CH3CH2CN + 4[H] —> CH3CH2CH2NH2
