14 - Alcohols Flashcards
What are the physical properties of alcohols compared to alkenes of the same length
o Are less volatile
o Have higher melting points
o Are more soluble in water
Do the differences increase or decrease as the length of the carbon chain increases
Decrease
Alcohols vs alkanes = strength of London forces
Do alkanes or alcohols have a higher boiling point
Alcohols = • Hydrogen bonds between alcohol molecules requires more energy to overcome than the weak London forces between alkane molecules
Explain this graph
• as the chain length increases, the contribution of the –OH group decreases and the alcohols resemble the alkanes more closely.
Are alcohols soluble in water
Yea
Why are alcohols soluble in water
• H bonds form between -OH group = very soluble
How do we classify alcohols
on number of H-atoms and R-groups attached to the C-atom that contains the OH group
What is a primary alcohol
1 R group
What is a secondary alcohol
Two R groups
What is a tertiary alcohol
What are the products when alcohols combust
• Same products as complete combustion of alkanes (carbon dioxide + water)
What type of reaction is the combustion of alcohols
Exothermic
How does chain length impact the combustion of alcohol
• The longer the chain, the more energy released per mole
Can primary alcohols oxidise
Yes
What product is formed when primary alcohols are oxidised
• Product = aldehyde, but can be further oxidised to form carboxylic acids
How to oxidise alcohol into an aldehyde
o Gentle heating with acidified potassium dichromate (H2SO4/K2Cr2O7 ) and primary alcohol
o Aldehyde must be distilled out as its formed (has lower B.P than alcohol so can be distilled)
o Prevents further oxidation into a carboxylic acid
o Dichromate (VI) ions turn from orange to green
chromium (III) ions
Has the dichromate ions been oxidised or reduced when making an aldehyde
Cr2O72- to Cr3+
- Has been Reduced
Product when ethanol has been oxidised
How to make a carboxylic acid from an aldehyde
o If the aldehyde is not distilled off, further refluxing with excess oxidising agent will oxidise it to a carboxylic acid
Can secondary alcohols be oxidised
Yes
What the product when a secondary alcohol is oxidised
Ketones
Does ketone need to be distilled off straight away and why
• Since ketones cannot be further oxidised, the ketone product does not need to be distilled off straight away after it has been formed
Write an equation for the oxidation of propan - 2 - ol
Can tertiary alcohols be oxidised
No
How would I turn alcohols into an alkene
Through the ELIMINATION REACTION
What is the elimination reaction also known as
The dehydration of alcohols
Process to dehydrate an alcohol
• Alcohol heated under reflux with an acid catalyst
o Excess hot, concentrated sulfuric acid or phosphoric acid is used as a catalyst
What type of catalyst is needed for dehydration
Hot concentrated sulfuric acid or phosphoric acid catalyst
What is eliminated in a dehydration reaction
A water molecule
What is the product of a dehydration reaction
Alkenes
What will the substitution reaction in an alcohol form
Haloalkane
How does the substitution reaction form a haloalkane
• a hydroxy group (-OH) is replaced by a halogen to form an haloalkane
Two steps to form a haloalkane
Form hydrogen halide
And then haloalkane
Process of substitution reaction
To prepare hydrogen halide
o Alcohol heated under reflux with sulfuric acid and a sodium halide (e.g., NaBr)
o Hydrogen halide formed in situ
To form haloalkanes
• Hydrogen halide reacts with alcohol to produce haloalkane
Write out the full equation of the subitution reaction of propan-2-ol with bromine
