Reactions of alcohols Flashcards
what are alcohols?
molecules with -OH bonded to a C chain
what can alcohols with small C chains do?
they are soluble in water, since they can form H bonds with H2O
what happens to primary alcohols when heated with acidified potassium dichromate, K2Cr2O7/H+?
- they are oxidised in 2 stages
- first to an aldehyde, then to a carboxylic acid
if you heat a primary alcohol with acidified potassium dichromate, K2Cr2O7/H+, but you only want the aldehyde, what do you need to do?
you need to limit the oxidation
- use the minimum amount of oxidising agent
- distill the product straight out of the mixture as it forms
what is the balanced equation for the reaction of primary alcohols with acidified potassium dichromate, K2Cr2O7/H+?
Ch3CH2OH + [O] => CH3CHO + H2O
so we get a carboxylic acid from a primary alcohol and acidified potassium dichromate, what do we need to ensure the oxidation goes as far as possible?
- use excess oxidising agent
- heat the mixture under reflux
what is reflux?
boiling liquid re-agents with a vertical condenser attached, prevents loss of reactants and products
what is the balanced equation from getting carboxylic acid from heating a primary alcohol with acidified potassium dichromate?
CH3CH2OH + 2[O] -> CH3COOH + H2O
what happens when you heat a secondary alcohol with acidified potassium dichromate?
oxidised in one step making a ketone
what happens when you heat a tertiary alcohol with acidified potassium dichromate?
- cannot be oxidised as there is no C-C bond to be broken
- no colour change from orange to green
what do you see if acidified potassium dichromate gets oxidised?
a colour change from orange to green as the acidified potassium dichromate gets reduced to Cr 3+
what are the conditions and reagents required for the dehydration of alcohols?
- pass vapour of the alcohol over a heated aluminium catalyst (Al2O3)
or - heat under reflux with concentrated H2SO4
what is an elimination reaction (eg. dehydration of alcohol)?
an elimination reaction is one in which a small molecule is removed from a larger molecule giving an unsaturated molecule (alkene)
what is esterification?
esters can be made from an alcohol and a carboxylic acid, the reaction is reversible
alcohol + carboxylic acid <=> ester + h2o
what are the conditions needed for esterification?
heat under reflux with an acid catalyst (either c. HCl or c. H2SO4)
