Alcohols Flashcards
How do alcohols react with oxygen?
Alcohols react with oxygen in the air when ignited and undergo complete combustion to form carbon dioxide and water
How can ethanol be produced sustainably as a fuel?
Ethanol can be produced sustainably as a fuel by the fermentation of sugars
Why does blending ethanol with gasoline make a better fuel than just ethanol?
Blending ethanol with gasoline or diesel increases the energy density and makes it safer in case of fires as it is easier to see the flames compared to pure ethanol burning
How are primary alcohols oxidised?
Primary alcohols can be oxidised to form aldehydes which can undergo further oxidation to form carboxylic acids.
The oxidising agent is acidified K2Cr2O7 (orange to green)
What colour does acidifed potassium dichromate turn when it is reduced?
orange -> green
orange dichromate (Cr2O72-) ions to green Cr3+ ions
What colour does acidified potassium manganate turn when it is reduced?
purple -> colourless
purple manganate ions (MnO4-) are reduced to colourless Mn2+ ions
How do you form an aldehyde from an alcohol?
A primary alcohol is added to the oxidising agent (acidified K2Cr2O7) and warmed.
The aldehyde product has a lower boiling point than the alcohol reactant so it can be distilled off as soon as it forms.
How do you form a carboxylic acid from an alcohol?
Form aldehyde by adding acidified K2Cr2O7 to primary alcohol.
If the aldehyde is not distilled off, further refluxing with excess oxidising agent will oxidise it to a carboxylic acid
How do you form a ketone from an alcohol?
Secondary alcohols oxidised under reflux with acidified K2Cr2O7 to form ketones.
Describe the dehydration of alcohols
Alcohol can undergo dehydration to form alkenes. This is an elimination reaction as a small (water) molecule is lost.
Alcohol vapour is passed over a hot catalyst of aluminium oxide (Al2O3) powder or pieces of porous pot.
Excess hot, concentrated sulfuric acid or phosphoric acid is used as a catalyst
Describe the substitution of alcohols
In the substitution of alcohols, a hydroxy group (-OH) is replaced by a halogen to form an haloalkane
The substitution of the alcohol group for a halogen can be achieved by reacting the alcohol with:
HX (rather than using HBr, KBr is reacted with H2SO4 or H3PO4 to make HBr that will then react with the alcohol)
Why can tertiary alcohols not undergo oxidation?
Tertiary alcohols cannot be oxidised.
To produce an aldehyde / ketone, a C-H must break to allow the C=O bond to form
Tertiary alcohols only contain C-C bonds attached to OH group
