Alcohols (reactions) Flashcards
What is the combustion reaction of alcohols?
They react completely in plentiful supply of oxygen to form carbon dioxide and water.
What is the dehydration reaction of alcohols?
Removal of water to produce an alkene and water.
Heated under reflux in presence of an acid catalyst (con. H2SO4, H3PO4)
What type of reaction is dehydration?
An elimination reaction.
In a vertical condenser (used in reflux) where does water go in and out?
Cold water in at the bottom, cold water out at the top.
What is the substitution of alcohols?
React with hydrogen halides. Halogen substitutes with OH from alcohol, producing a haloalkane and water.
Conditions:
- Heat under reflux with H2OS4 and sodium halide.
Halogen halide is made in situ and then reacts with the alcohol
What alcohols can be oxidised?
Primary and secondary can be oxidised by heating with an oxidising agent [O], producing water as well.
Tertiary alcohols cannot be oxidised.
What is the most common oxidising agent?
Acidified potassium dichromate (VI) (K2Cr2O7/H2SO4)
The dichromate (VI) ions, Cr2O72- are reduced to chromium 3+ ions, Cr3+.
Orange to green
What are primary alcohols oxidised to?
An aldehyde or carboxylic acid.
How do you make an aldehyde from a primary alcohol?
Oxidation by distillation. The aldehyde distils out of the reaction mixture as the condenser is angeled downwards, dripping into a flask. This prevents it from being oxidised into a carboxylic acid.
How do you make carboxylic acid from a primary alcohol?
Oxidation by reflux. The condenser is vertical. The aldehyde remains in the reaction mixture and is further oxidised to a carboxylic acid.
What are secondary alcohols oxidised to?
A ketone and water. Under distillation or reflux. Need acidified potassium dichromate (K2Cr2O7/H2SO4)
Why is reflux preferred when oxidising a secondary alcohol?
To make sure all the alcohol is reacted.
