4.3 alcohols and phenols Flashcards
1
Q
what is a primary alcohol?
A
an alcohol that has one carbon atom directly bonded to the carbon of the -OH group
2
Q
what is a secondary alcohol?
A
an alcohol that has two carbon atoms directly bonded to the carbon atom of the -OH group
3
Q
what is a tertiary alcohol?
A
an alcohol that has three carbon atoms directly bonded to the carbon atom of the -OH group
4
Q
what are the two common methods of forming primary and secondary alcohols?
A
- from halogenoalkanes by nucleophilic substitution
- from carbonyls by reduction
5
Q
what type of reaction is the one forming an alcohol from a halogenoalkane?
A
nucleophilic substitution
6
Q
what are the conditions for forming an alcohol from a halogenoalkane?
A
- NaOH (aqueous)
- heat
- reflux
7
Q
what type of reaction is one forming an alcohol from a carbonyl?
A
reduction
8
Q
what does reducing an aldehyde produce?
A
primary alcohol
9
Q
what does reducing a ketone produce?
A
secondary alcohol
10
Q
what is the usual reducing agent for the formation of alcohols from carbonyls?
A
- sodium tetrahybridoborate (III), NaBH4, dissolved in water
- but is acceptable to represent it as [H] in equations and balance in the usual way
- but is not powerful enough to reduce carboxylic acids so lithium tetrahydriodoaluminate (III), LiAlH4, dissolved in ethoxyethane/dry ether solvent can be used instead
11
Q
what are the three reactions of alcohols?
A
- reaction with hydrogen halodes
- reaction with carboxylic acids
- reaction with ethanoyl chloride
12
Q
what is the reaction of alcohols with hydrogen halides?
A
- reacting primary or secondary alcohols with hydrogen halides produce halogenoalkanes
- the most appropriate method depends on which halogen is to be substituted
13
Q
why can NaBH4 dissolved in water be used in the formation of alcohols from carbonyls?
A
- it is the reducing agent which provides the H- ion for the reaction
14
Q
what type of reaction is the one between alcohols and hydrogen halides?
A
nucleophilic substitution
15
Q
what is a disadvantage of the reaction between alcohols and hydrogen halides?
A
- its generally slow and reversible
- and often gives poor yields
16
Q
what happens in chlorination? (the reaction between alcohol and the hydrogen halide of chlorine)
A
- pass hydrogen chloride gas into the alcohol
- in the presence of anhydrous zinc chloride (acts as a catalyst)
- or chloroalkanes can also be produced from alcohols using phosphorus (V) chloride, PCl5
- alcohol + PCl5 —> chloroalkane + POCl3 + HCl
- (but phosphorus (V) oxide trichloride, POCl3, is a liquid and needs to be removed. if the halogenoalkane has a similar boiling point to it then separation becomes difficult)
17
Q
what are the conditions for the reaction of alcohols with hydrogen halides: hydrogen chloride?
A
- hydrogen chloride gas, HCl
- anhydrous (dry) zinc chloride catalyst, ZnCl2
- heat
18
Q
what happens in bromination? (the reaction between alcohol and the hydrogen halide of bromide)
A
- an ‘in situ’ reaction
- alcohol, potassium bromide, KBr, and (50%) concentrated sulfuric (VI) acid is heated
- this produces the hydrogen bromide in-situ
- this then reacts with the alcohol to produce a bromoalkane
- CH3CH2OH + KBr + H2SO4 —> CH3CH2Br + KHSO4 + H2O
19
Q
what happens in iodination? (the reaction between alcohol and the hydrogen halide of iodine)
A
- warm damp red phosphorus and iodine together
- to form phosphorus (III) iodide, PI3
- which then reacts with the alcohol present
- 2P + 3I2 —> 2PI3
- 3CH3CH2OH + PI3 —> 3CH3CH2I + H3PO3
20
Q
what does an alcohol react with a carboxylic acid to produce?
A
- an ester
- and water
21
Q
what type of reaction is the reaction between an alcohol and carboxylic acid?
A
esterification / addition-elimination
22
Q
what are the conditions required for the reaction between an alcohols and carboxylic acid?
A
- concentrated sulfuric acid, H2SO4
- heat
23
Q
what happens in the reaction between alcohols and carboxylic acids?
A
- are refluxed together with concentrated sulfuric acid, which acts as a catalyst
- alcohol + carboxylic acids—> ester + water
- the reaction is reversible
- to increase the yield of the ester, some sulfuric acid is added and the mixture is heated under reflux
- the products can then be distilled and the ester collected
24
Q
what is happening in the reaction between alcohols and ethanoyl chloride?
A
- the (primary or secondary) alcohol reacts with ethanoyl chloride, CH3COCl, to form an ester and hydrogen chloride
- this method gives a better yield of an ester than using a carboxylic acid, as the reaction is not reversible
- however, the cost of acid chlorides means that this is not a cost-effective process in industry
25
what type of reaction is the reaction between alcohol and ethanoyl chloride?
nucleophilic addition-elimination
26
what is a phenol?
- an aromatic compound with an -OH group directly bonded to a benzene ring
27
if other groups are bonded to the benzene ring, the compound is names according to the position of the substituted group
- e.g 2-cholophenol
28
the presence of the benzene ring tends to (weaken/strengthen) the OH bond
weaken
- this means that phenols are weakly acidic in aqueous solutions as protons are lost
29
what is phenol’s acidity due to?
- the lone pair of electrons on the oxygen overlapping with the π electron system of the ring
- this causes the hydrogen ion to be lost more easily, forming the phenoxide ion
30
why is the phenoxide ion more stable than expected?
- as the negative charge tends to be spread ‘around’ the ring
31
does phenol react with sodium hydroxide?
does it react with sodium carbonate?
- phenol is acidic enough to react with sodium hydroxide (NaOH)
- but it doesnt react with sodium carbonate (Na2CO3)
32
does carboxylic acid react with sodium hydroxide?
does it react with sodium carbonate?
- yes
- yes
33
what is a test to distinguish between phenols and carboxylic acids?
- using sodium carbonate
- phenols dont react with sodium carbonate but carboxylic acids do
34
what is the order of acidity between phenols, alcohols and carboxylic acids?
carboxylic acids > phenols > alcohols
35
what type of reaction do phenols react by? why?
electrophilic substitution
- due to the delocalised electron system
36
are phenols more reactive than benzene?
why?
yes
- the increased reactivity of phenol is because of the loan pair of electrons on the oxygen atom
- this electron pair is delocalised into the ring structure
- this increases the electron density of the ring, making it more susceptible to attack from electrophiles
37
do phenols react with bromine?
yes
(generally carried out in aqueous solution)
38
what do phenols react with bromine to produce?
- 2,4,6-tribromophenol
- as an immediate white ppt
- the orange bromine water is decolourised
- this reaction can be used as a test for phenol
39
what are the two reaction of phenols we need to know?
- reaction of phenols with bromine water
- reaction of phenols with ethanoyl chloride
40
what type of reaction is the one between phenols and ethanoyl chloride?
nucleophilic addition-elimination
41
what do phenols react with ethanoyl chlorides to form?
aromatic esters
- such as phenyl ethanoate
(and hydrogen chloride HCl)
42
which reaction is slower: the reaction between phenols and ethanoyl chloride or the reaction between alcohols and ethanoyl chloride?
phenols and ethanoyl chloride
43
why is the reaction between phenols and ethanoyl chloride slower than the reaction between alcohols and ethanoyl chloride?
- the delocalisation of an electron pair from the oxygen atom in a phenol means that it is more difficult for a phenol to react as a nucleophile
44
what are 2 tests that can be used to identify a phenol group?
- reaction with bromine water
- reaction with iron (III) chloride solution
45
what is a positive result for a phenol in the reaction with bromine water?
- white ppt produced
- the orange bromine water is decolourised
46
what is a positive result for a phenol in the reaction with iron (III) chloride?
- a vivid purple colour
(with the addition of yellow iron(III) chloride solution)
47
what type of reaction can a halogenoalkane undergo to form an alcohol?
nucleophilic substitution
48
what acts as the nucleophile in the reaction between chloroethane and warm aqueous sodium hydroxide?
- the hydroxide ion from sodium hydroxide
- OH-
49
name the type of reaction for the formation of alcohols from aldehydes and ketones
reduction
50
give the reducing agent for the reduction of aldehydes and ketones to alcohols
NaBH4 dissolved in water
51
what reagent is required to reduce carboxylic acids to alcohols?
LiAlH4
52
why is NaBH4 used for the reduction of aldehydes and ketones but not for carboxylic acids?
NaBH4 is not reactive enough to reduce carboxylic acids
53
why are primary and secondary alcohols useful for organic synthesis reactions?
- the OH- functional group is able to react with various different compounds
54
what type of organic product is produced in the reaction between alcohols and hydrogen halides?
halogenoalkanes
55
what catalyst is required for the reaction of primary and secondary alcohols with hydrogen chloride?
anhydrous zinc chloride
56
what are the reagents required for the reaction of ethanol to form bromoethane?
- instead of directly adding hydrogen bromide, ethanol requires a mixture of potassium or sodium bromide and concentrated sulfuric acid
- this will produce the hydrogen bromide which will react with ethanol to form bromoethane
57
name the mechanism for the reaction between acyl chlorides and alcohols
nucleophilic addition-elimination
58
what catalyst is required for an esterification reaction?
- the alcohol and c/a must be heated in the presence of a strong acid catalyst
- e.g concentrated sulfuric acid
59
name the ester formed in the reaction between butanouc acid and propanol
propyl butanoate
60
what are the identifying properties of esters?
- sweet smelling
- so often used in flavourings and perfumes
- have low boiling points
- and make good solvents for other polar molecules
61
what is the acidity of phenol?
- very weakly acidic
- pH between 5 and 6
62
what is the name of the product formed when phenol reacts with ethanoyl chloride?
phenyl ethanoate
63
if a molecule has two or three -OH groups they are called ____ and _____ respectively
- diols
- triols
64
what are the conditions for the making of alcohols by fermentation? (AS)
- 30-35°C
- zymase enzyme
- anaerobic conditions
- filtering and then distill
65
what is the equation for the making of alcohols by fermentation?
glucose —> ethanol + carbon dioxide
66
why is the making of alcohols by fermentation carried out in anaerobic conditions?
otherwise the ethanol is oxidised to vinegar
67
what are the conditions for making alcohols from alkenes?
- 300°C
- 60-70 atm
- conc sulfuric or phosphoric acid catalyst
68
what type of reaction is the one making alcohols from alkene?
hydration / addition reaction
69
what happens in the reaction making alcohols from alkene?
- steam and ethene are passed over a catalyst of conc sulfuric or phosphoric acid
70
what are the conditions for the reaction of alcohols to alkenes by dehydration/elimination? (AS)
- conc sulfuric acid
- 170°C
71
how do you make the oxidising agent acidified potassium dichromate?
- add potassium dichromate and sulfuric acid together
72
what is the reverse of esterification called?
hydrolysis
73
if the reaction of esterification is reversible, what applied?
le chatelier
74
what are the conditions for esterification?
- H2SO4 or HCl catalyst
- reflux
75
why do you use a dry ether solution with the LiAlH4 in reducing carbonyls?
its moisture sensitive
76
out of LiAlH4 and NaBH4, which is the stronger reducing agent?
- LiAlH4
77
an acid chloride contains a ____ group
COCl
78
why are acid chlorides (acyl chlorides) highly susceptible to nucleophilic attack?
- Cl and O are electronegative, so they have a massive delta + on C atom
- (so are extremely reactive)
79
acyl (acid) chlorides are highly exothermic when they react. what do they give off when they react?
- ‘fuming’ hydrogen chloride gas
(white fumes)
(so need to be done in a fume cupboard)
80
- adding an acyl group to what we’re reacting with it - call it an acylating agent
81
how do you name an acyl chloride?
- add -oyl chloride to the name
- e.g 2,2-dimethyl propanoyl chloride
82
what are the conditions for the reaction of acid chlorides in making esters?
(acid chloride + alcohol —> ester)
- room temperature and pressure
- add alcohol dropwise
83
what is the reaction of acid chlorides in making carboxylic acids?
acid choride + water —> carboxylic acid + HCl (g)
84
what are the conditions for the reaction of acid chlorides in making carboxylic acids?
- room temperature and pressure
- add water dropwise
85
what is the reaction of acid chlorides in making amides?
acid chloride + ammonia —> amide
86
what are the conditions for thr reaction of acid chlorides in making amides?
- room temperature and pressure
- add amine/ammonia dropwise
87
a phenol is an aromatic alcohol
88
what will phenols react with the strong base sodium hydroxide to produce?
sodium phenoxide and water
89
why is phenol slightly acidic?
- due to the overlap, the C-O strengthens
- π bond has partial double bond character
- H bond breaks
- lose H+
- proton donor
90
what is the reaction of phenols with strong bases?
phenol + KOH/NaOH —> phenol with O- and K+ (K+ not bonded but next to O-) + H2O
91
in reactions of phenols with bromine, can only bromonate at 2,4,6 if available
92
why is phenol more reactive than benzene?
- phenol readily reacts with other substances while benzene needs to be forced to react
- this means that something in its structure must make it more reactive than benzene
- the electron density in the benzene ring must be greater than that of benzene
- the difference between benzene and phenol is the Oh group
- the oxygen atom in the OH group has a lone pair of p orbital electrons
- these can delocalise with the p electrons in the benzene ring
93
how do you test for a phenol?
add iron (III) chloride / FeCl3
- a blue-violet/purple solution should form
