Unit 4.3 - Alcohols and Phenol Flashcards
Alcohols
Compounds with one or more hydroxy (-OH) groups attached to the aliphatic chain
Phenols
Compounds where the hydroxy groups are directly attached to the benzene ring
Why are phenol and alcohols chemically different and react differently?
Because of the interaction between the oxygen atom and the benzene ring
How do we name alcohols?
Alcohols with one hydroxy group form a homologous series - the suffix -ol is added to the alkane stem
What are propan-1-ol and propan-2-ol to each other?
Structural isomers
Primary alcohols
The carbon which carries the OH- group is only attached to 1 alkyl group (1 other Carbon atom_
Secondary alcohols
The carbon which carrier the OH- group is attached to 2 alkyl groups (which may be the same or different)
Tertiary alcohols
The carbon which carries the OH- group is attached to 3 alkyl group s
What does Butan-2-ol form and why?
Optical isomers
Has a chiral centre
Explain in detail the solubility of alcohols
The lower alcohols (shorter chain) are completely soluble in water (are able to form hydorgen bonds with water)
As the alkyl (hydrocarbon) chain increases in length, the contribution of the hydrogen bond to the overall intermolecular forces decreases = the higher alcohols from butanol onwards are not very soluble in water
Why are lower alcohols completely soluble in water whereas longer ones aren’t?
Shorter = are able to form hydrogen bonds with water
Longer = the contribution of the hydrogen bond to the overall intermolecular forces decreases
How come hydrogen bonds between alcohols and water form?
Highly polarising + hydrogen atom attracts a lone pair of electrons from a small, highly electronegative atom in another molecule (N, O, F)
Compare the boiling point of alcohols to the boiling points of alkanes of similar molar mass
Higher
Which bonds do not break when a covalent compound boils?
Covalent bonds
Why do alcohols have higher boiling points than alkanes of similar molar mass?
Alkanes only have induced dipole-induced dipole forces
Alcohols have additional hydrogen bonding that elevate the boiling temperature
Which has the highest boiling point - ethanol or propane? Why?
Ethanal
It has hydrogen bonds which require more energy to break than the intermolecular forces in ethanol
How will ethanol dissolve in water?
As hydrogen bonds form between ethanol and water
What will ethanol dissolve in as well as water and why?
Non-polar solvents
Due to the presence of the hydrocarbon chain
Why is ethanol an important solvent?
Will dissolve in both water and non-polar solvents
What else do we need to consider on top of the intermolecular forces when working out boiling points? Explain
Chain lengths
Longer chain lengths = increased boiling points due to increased van der wall atracctions
Therefore, the higher the Mr or a molecule, the higher the boiling point
Why do longer chain lengths lead to higher boiling points?
Increased Van der Waal attractions
Explain and give the conditions and equation for the preparation of alcohols from alkenes. What type of reaction is this?
Ethanol is produced industrially by the steam hydrolysis of ethene
Phosphoric acid catalyst/concentratd sulfuric acid
300C
60 atm pressure
CH2=CH2 + H2O (g) —> CH3CH2OH
Electrophillic addition
What is the more natural way to produce ethanol that doesn’t involve steam hydrolysis of ethene?
By fermentation
How can ethanol be made by fermentation?
Fermentation followed by distillation
What happens during fermentation?
Sugars (glucose) from plants are converted into Hanoi by the action from enzymes in yeast (zymase)
Enzymes in yeast and what they do
Zymase
Convert sugars (glucose) form plants into ethanol
Why is fermentation a good way to produce ethanol?
Carbon neutral
More sustainable
Temperature required much lower than the industrial process
Equation for the fermentation of glucose to produce ethanol
C6H12O6 (aq) —> 2C2H5OH (aq) + 2CO2 (g)
What temperature is used during fermentation of glucose for ethanol? Explain why
35C
It’s a compromise since the reaction is slow at low temperatures and enzymes which bring down the enegry required are denatured at high temperatures
The temperature is much over than the industrial process
Why is air kept out of the reaction vessel during fermentation?
Otherwise the ethanol will react (oxidise) to form ethanoic acid —> vinegar
When does fractional distillation occur during the production of ethanol via fermentation?
Once the solution contains 15% ethanol
Why is a fractioning column needed during the fermentation of glucose to produce ethanol?
As we have small differences in boiling temperatures
Boiling point of ethanol
78C
How is the ethanol distilled off during fermentation?
Using frictional distillation
Process that has to be stopped and restarted?
Batch process
What type of process is fermentation known as and why?
Batch process
Has to be stopped and restarted
How are alcohols produced from halogenoalkanes?
The halogenoalkane is refluxed with aqueous sodium hydroxide
This is the alkaline hydrolysis of a halogenoalkane
If the sodium hydroxide used to reflux with the halogenoalkane to produce alcohol was ethanolic as opposed to aqueous, what kind of reaction would it be?
Elimination reaction
Method for preparing a pure sample of butan-1-oil from 1-bromobutane
- Measure 25cm^3 of CH3CH2CH2CH2Br using a measuring cylinder and decant to a 100cm^3 round bottomed flask. This step should be performed in a fume cupboard (toxic)
- Add 25cm^3 of 0.1moldm^3 NaOH (irritant) solution and a few anti-bumping granules in to the round bottom flask. This should also be performed in the fume cupboard.
- Swirl the flask gently to mix the reagents and set up the reflux condenser apparatus for refluxing
- Turn on the water to run through the condenser
- Turn on the heating mantle (or hot plate, or Bunsen burner) and heat the solution to reflux for 15 minutes
- Rearrange the apparatus for distillation
- Distilled off the CH3CH2CH2CH2OH produced and collect in a clean, dry 100cm^3 conical last
- Record the temperature at which eh liquid product is collected
Why do we need anti-bumping granules when preparing alcohol from a halogenoalkane?
Since 2 unmissable liquids will bump, especially under heat
What’s another way of avoiding bumping (except for using anti-bumping granules)?
Using a larger container
How do anti-bumping granules prevent bumping?
By preventing large bubbles
Why is reflux used?
To avoid loss of reagents/products
Why should the escape of vapour be prevented when refluxing?
Since complete oxidation could not occur
Since vapour is flammable
Since the yield would be reduced
Why do we use a heating mantle when preparing an alcohol from a halogenoalkane?
Alcohol is flammable and could ignite with a naked flame
How long do we reflux for?
Long enough to enough to establish equilibrium
Where should a thermometer be during distillation and why?
Opposite the opening of the condenser since were measuring the temperature of thee vapour
Why do we use a fractionating column?
Since we have small differences in boiling temperatures
How does a thermometer help to determine purity?
By measuring the boiling point
Why is water put at the bottom of a reflux condenser?
Allows better cooling
What type of reaction is the reaction between a halogenoalkane and NaOH to make an alcohol and why?
Nuelcophilic substitution
OH- ion is the nucleophile
Reflux
The constant flow of evaporation and condensation and is a reaction technique
Heat volatile (easily evaporated at normal temperatures) reactants
Volatile
Easily evaporated at normal temperatures
What type of reactants are heated when refluxing?
Volatile ones
volatile
Easily evaporated at normal temperatures
Fractional distillation
A separation technique that separation molecules based on their boiling temperatures
What are primary alcohols formed from the reduction of?
Aldehydes
What are secondary alcohols formed form the reduction of?
Ketones
What is formed from the reduction of aldehydes?
Primary alcohols
What is formed form the reduction of ketones?
Secondary alcohols
Reducing agent when reducing aldehydes and ketones to form alcohols
Sodium borohydride, NaBH4
Sodium borohydride purpose when forming primary and secondary alcohols from aldehydes and ketones
Reducing agent
Stronger reducing agent to use than NABH4 during the reduction of carbonyl compounds
LiAlH4
How is the reaction carried out when reducing carbonyl compounds?
By refluxing the reagents
Shorthand for oxidation and reduction
[O] [R]
What kind of reactions are those for going from aldehydes and ketones to alcohols?
Reversible
Are carboxylic acids easily reduced? How do you know?
No
They’re not reduced by NaBH4
What are carboxylic acids reduced by and to what?
Lithium aluminium hydride (LiAlH4) to primary alcohols
How are primary alcohols formed form carboxylic acids?
The acid is reacted with LiAlH4 dissolved in ether at room temperature
Conditions for reducing carboxylic acids to form primary alcohols
Dry conditions
Why must the reduction of carboxylic acids to primary alcohols be done under dry conditions?
As LiAlH4 reacts violently with water
Test for alcohols + results
Acidified dichromate solution
Primary —> carboxylic acid
Secondary —> ketone
Tertiary —> no reaction
Colour change from orange to green
What is happening to cause the colour change from orange to green when adding acidified dichromate solution to alcohols?
The dichromate (VI) ion is reduced to the chromium (III) ion
Why do alcohols form hydrogen bonds?
The OH bond in alcohols is highly polar. It’s able to form hydorgen bonds as hydrogen is bonded with. Highly electronegative atom
What does NaBH4 not reduce?
Carboxylic acids
What happens to the =O bond when reduced to form alcohols?
Replaced with OH and H
Carbonyl groups
C=O
How do we work out how many C=O groups are present after a reaction of a ketone to form an alcohol?
For every carboxyl, the number of hydrogen toms will increase by 2
Conditions and oxidising agent when oxidising alcohols
Potassium dichromate (VI) acidified with concentrated sulfuric acid
Heated
Acidified potassium dichromate symbol
H+/Cr2O7^2- or H+/K2Cr2O7
What happens to ethanol when distilled and what happens when refluxed?
Distilled = ethanal
Refluxed = ethanoic acid
What is a primary alcohol immediately converted into when heated with acidified potassium dichromate (vI) and why?
Aldehyde is immediately formed since the reaction is exothermic enough
Why does a primary alcohol need to be refluxed to form a carboxylic acid?
Not exothermic enough
What are aldehydes formed from the oxidation of?
Primary alcohols
What are ketones formed from the oxidation of?
Secondary alcohols
What does a secondary alcohol form when it undergoes oxidation with acidified potassium dichromate (VI)?
A ketone
When does a carboxylic acid not form when oxidising an alcohol?
When it’s a secondary alcohol that’s formed a ketone
Why are ketones resistant to further oxidation?
As they do not possess an oxidisable hydrogen
There’s no hydrogen attached to the carbonyl group
Oxidisable hydrogen
Hydrogen attached to the carbonyl group
What happens to the dichromate (VI) ion during the oxidation of alcohols reactions and what does this do?
Cr2O7^2- is reduce to Cr^3+
Colour change from orange to green
How does Cr3+ behave with NaOH?
Amphoterically
Dichromate (VI) ion
Cr2O7^2-
Conditions for the dehydration of primary alcohols
Reacted with concentrated sulfuric acid (in excess)
170C
Main Product of the dehydration of a primary alcohol
Alkene
Why is sulfuric acid used during the dehydration of primary alcohols?
It removes the elements of water from the alcohol
What type of reaction is the dehydration of primary alcohols?
Elimination reaction
Conditions for the chlorination of alcohols
Hydrogen chloride gas is passed into the alcohol in the presence of anhydrous zinc chloride, which acts as a catalyst
Type of reaction during the chlorination of alcohols
Nucleophilic substitution
Conditions for the bromination of an alcohol
Carry out an “in situ” reaction
A mixture of alcohol, potassium bromide and 50% sulfuric acid is heated
How does sulfuric acid aid the formation of the halogenoalkane during the bromination of an alcohol?
It removes the water formed in the reaction and aids the bromination process since it prevents the reverse reaction taking place since the reaction is reversible
Equation for the chlorination of butan-1-oil
CH3CH2CH2CH2OH —> CH3CH2CH2CH2Cl + H2O
Equation for the dehydration of ethanol
CH3CH2OH —><— CH2=CH2 + H2O
Equation for the bromination of butan-1-ol’
CH3CH2CH2CH2OH + KBr + H2SO4 —> CH3Ch2CH2CH2Br + KHSO4 + H2O
Conditions for the iodination of alcohols
Warm damp red phosphorus and iodine together to form phosphorus (III) iodide, PI3, which then reacts with the alcohol present
2 equations for the 2-step process of the iodination of alcohols
2P + 3I2 —> 2PI3
3CH3CH2CH2CH2OH + PI3 —> 3CH3CH2CH2CH2I + H3PO3
How does the iodination of alcohols work?
One of the iodines replaces the OH
Why do we need to be careful with white phosphorus?
It spontaneously combusts
What is ethanol chloride?
An acid chloride
Ethanoyl chloride formula
CH3COCl
Describe ethanoyl chloride as a compound
Very reactive
Conditions for the reaction of alcohol with ethanoyl chloride
Room temperature
Anhydrous (dry) conditions
Fume cupboard (harmful HCl gas)
Why should the reaction between alcohol and ethanoyl chloride be carried out in a fume cupboard?
Due to the release of harmful hydrogen chloride gas
Equation for the reaction between ethanoyl chloride and ethanol
CH3COCl + CH3CH2OH —> CH3COOCH2 + HCl
Ethyl ethanoate
CH3COOCH2CH3
What is formed during the reaction between propan-2-ol and ethyl ethnote?
The ester CH3COOCH(CH3)2 is formed
(1-methylethyl ethanoate)
What can the reaction between alcohols and ethanoyl chloride be used for?
To produce an ester form phenol
Why can’t we react phenol and carboxylic acids to form an ester?
Phenol doesn’t behave as an alcohol
Reaction between alcohols and carboxylic acid
Forms an ester and water
How is an ester formed from a reaction between alcohols and carboxylic acids?
The reaction mixture is refluxed with concentrated sulfuric acid
Reaction between an alcohol and carboxylic acid
Ester + water
What type of reaction is that between an alcohol and a carboxylic acid
Reversible
Describe the reaction between alcohol and carboxylic acid
Very slow
What is needed for the reaction between an alcohol and a carboxylic acid to go to completion?
Concentrated sulfuric acid
Explain how the concentrated sulfuric acid works when reacting an alcohol and carboxylic acid
It speeds up the reaction by acting as a catalyst and as a dehydrating agent by removing water form the reaction mixture. In doing so, the position of equilbirium is pushed to the right and the reaction can go to completion
Which reaction is preferred for making esters - the reaction of alcohols with ethanoyl chloride or with carboxylic acids?
Reaction with ethanoyl chloride
Why is the reaction of alcohols with ethanoyl chloride preferred for making esters over the reaction with carboxylic acids?
The reaction of alcohols with ethanoyl chloride is not an equilbirium reaction - it’s one directional, whereas the reaction with carboxylic acids is an equilbirium reaction
It’s easier to separate the co-products with the reaction with ethanoyl chloride since HCl naturally evaporates
Describe the hydroxy (OH) group in phenols
Is bonded to the benzene ring
Why are some of the properties of phenol different to those of alcohols?
Since the OH group is directly bonded to the benzene ring in phenols
Molecular formula of phenol
C6H5OH
Melting point of phenol
40-43C
Solubility of phenol in water + explanation
Moderately soluble (can form hydorgen bonds with water)
What happens if you try to dissolve too much phenol in water?
You get 2 layers of liquid
Top layer = phenol in water
Bottom layer = water in phenol
Toxicity of phenol
Quite toxic via oral exposure
Explain why the reactivity of phenol is different to that of alcohols
One of the lone pairs of the oxygen atom can overlap with the delocalised pi system to form a more extended delocalised system in phenol
Therefore, the C-O bond in phenols is shorter and stronger than in alcohols
Why is the C-O bond shorter and stronger in phenols than in alcohols?
One of the lone pairs of the oxygen atom can overlap with the delocalised pi system to form a more extended delocalised system in phenol
Is C-O bond fission in a phenol easier or harder than C-O bond fission in an alcohol? Why?
Harder
The C-O bond in phenols is shorter and stronger than in an alcohol
What are more susceptible to attack by electrophiles - phenol or alcohol? Why?
Phenol
Due to the extended delocalisation (caused by the lone pairs on the oxygen atom overlapping with the delocalised pi system to make a more extended delocalised system) creating a higher electron density in the ring
What are the most acidic - phenols or alcohols?
Phenols are much more acidic than alcohols
What are the strongest acids out of these - phenol, ethanol, ethanoic acid?
Phenol is a stronger acid than ethanol but a considerably weaker acid than ethanoic acid
What does the ionisation of phenol give?
The phenoxide ion, C6H5O-
Phenoxide ion
C6H5O-
Where does the position of equilibrium lie in the equation for the ionisation of phenol?
To the left
What gives added stability to the phenoxide ion?
Delocalisation of the negative charge
Why is phenol not very soluble in water?
Since the Oh- group is only a small part of a largely hydrophobic molecule
What does phenol dissolve in readily and what does this giv?
Aqueous NaOH
To give a solution of sodium phenoxide
What is an example of phenol reacting as an acid? Explain
When it dissolves readily in aqueous NaOH
Phenol loses a proton to the aqueous OH- ion present from NaOH
What affects the acidity of phenol?
The presence of substituents on the benzene ring
What is phenol not strong enough to react with since it’s only a weak acid?
Sodium carbonate or sodium hydrogencarbonate to produce CO2
Test to distinguish between a simple aliphatic acid (e.g - ethanoic acid) and phenol
Add sodium carbonate solution
Ethanoic acid —> bubbles of CO2
Phenol —> no results
What activates the ring of phenol to attack by electrophiles?
The presence of an OH- group bonded directly to the benzene ring
What does the presence of an OH- group on phenol activates it to?
Attack by electrophiles
Which positions are activated towards attack by electrophiles in phenol?
All of them, but the 2-, 4- and 6- positions are activated to a greater extent
What does it mean since the 2-, 4- and 6- positions on phenol are activated to a greater extent for attack from electrophiles?
An incoming substituent is likely to replace a hydrogen atom at one or more of these positions
What is formed when phenol is treated with dilute nitric acid?
Both 2- and 4- nitrophenol
What polarises bromine when phenol reacts with bromine?
The increased electron density in the ring
What is used when phenol reacts with bromine?
Aqueous bromine (bromine water)
What is produced when bromine water reacts with phenol?
A white precipitate of 2, 4, 6 - tribromophenol
Conditions for the reaction of phenol with bromine
Cold
No catalyst
Why is bromine described to be “decolorised” during its reaction with phenol?
Since aqueous bromine is an orange solution and the products of the reaction are a colourless solution and a white precipitate
What reaction can be used as a test for phenol?
The reaction between phenol and bromine
Explain why bromine is used as a test for phenol
When adding bromine, the result is different from the reaction of bromine with an alkene as the reaction with phenol results in the decolorisation of bromine with the additional formation of a white precipitate
Mechanism for the reaction between phenol and bromine
Electrophilic substitution
What happens during the reaction between phenol and bromine if the 2-, 4- and 6- positions of a phenol are already blocked by a substituent?
Bromine generally substitutes in the remaining 2-, 4- and 6- positions
What does the reaction between 2-methyl phenol and bromine give?
4-6-dibromo-2-methyl phenol
What does the reaction between 3-methyl phenol and bromine give?
2-4-6-tribromo-3-methyl phenol
What happens in the reaction between 2-4-dinitrophenol and bromine? Why?
6-bro o-2,4-dinitrophenol
Only the 6-position is free for substitution
How can alcohols and phenols react as nucleophiles?
By the use of their oxygen lone pairs
Why is it more difficult for phenol to react as a nucleophile than alcohol?
The delocalisation of an electron pair from the oxygen atom in phenol means that it is more difficult for a phenol to react s a nucleophile
Why are carboxylic acids not suitable reagents to make an ester with phenol?
Because in the reaction with a carboxylic acid to give an ester, the phenol needs to act as an electrophile
However, the delocalisation of an electron pair from the oxygen atom in phenol means that it is more difficult for a phenol to react as a nucleophile
Describe the reaction between phenol and ethanoyl chloride
Slow at room temperature
What is used to speed up the reaction between phenol and ethanoyl chloride?
A base such as pyridine, C5H5N
Pyridine
C5H5N
C5H5N
Pyridine
What pyridine do during the reaction between phenol and ethanoyl chloride?
Reacts with the hydrogen chloride co-product to give pyridinium chloride, C5H5NH+Cl-
What is often used instead of ethanoyl chloride for its reaction with phenol and why?
Ethanoic anhydride
Ethanoyl chloride is an expensive reagent
What can be used if phenol is reacted with a less reactive acyl chloride? Why?
Aqueous conditions
As the acyl chloride in only slowly hydrolysed by water
Less reactive acyl chloride than ethanoyl chloride
Benzoyl chloride
Benzoyl chloride
C6H5COCl
What is done during the reaction between phenol and benzoyl chloride (less reactive than ethanoyl chloride)?
Phenol is added to aqueous NaOH
The mixture is shaken
What is the main test for phenols?
Test with neutral aqueous iron (III) chloride
What is the result of the test for phenols with neutral aqueous iron (III) chloride?
A purple colour in aqueous solution is produced
How is the purple colour produced in the reaction between phenol and neutral aqueous iron (III) chloride?
A complex is formed between the two reagents
What will happen when any compound that contains an -OH group bonded directly to a benzene ring is reacted with iron (III) chloride?
It will give a brightly coloured complex
Generally these are purple, blue or green in colour
What can the reaction between phenol and aqueous iron (III) chloride be used for?
As a test to differentiate between an aliphatic alcohol and a phenol
What are the 2 common drug obtained from phenol
Aspirin
Paracetamol
Formula for aspirin
C9H8O4
Systematic names for aspirin
2-acetoxybenzoic acid
Or
Acetylsalicylic acid
Uses for aspirin
Anaesthetic
Disadvantages of aspirin
Bleeding risks, aspirin poisoning from overdosing
Conditions for the production of aspirin from phenol?
Heat
Pressure
Explain the test to test that no salicylic acid remains as an impurity after the reaction to produce aspirin
Add neutral iron (III) chloride
Would give a purple solution of phenol was present (and notice that salicylic acid is both an acid and a phenol since it was an OH group bonded to the benzene ring)
Why is salicylic acid also a phenol?
Has an OH group bonded to the benzene ring
% yield equation
Actual/theoretical x100
If we have an OH group directly bonded to a benzene ring, what do we need to remember to do when naming functional groups?
One of the functional groups is NOT alcohol, it’s phenol
What would happen when aqueous sodium hydroxide is added to phenol and why?
Na will substitute with the H in OH too since phenol is acidic
How do we separate the products of nitration?
By fractional distillation
How do we convert an alcohol into an alkene? Explain
Use sulfuric acid since it’s a dehydrating agent
How many products would form when we have a symmetrical alcohol compared to an asymmetrical alcohol when reacting an alcohol with sulfuric acid to form an alkene?
One product forms when we have a symmetrical alcohol
More than one product forms when we have an asymmetrical alcohol
What do we get when adding sulfuric acid to an alcohol and why?
Alkene
Sulfuric acid is a dehydrating agent
What does sulfuric acid act as?
A dehydrating agent
Asymmetrical alcohol
OH in the middle of
