Unless the -OH group is converted into a better leaving group, then
alcohols are poor substrates for substitution reactions.
Protonation to convert the leaving group into H2O has limited
utility as not all substrates or nucleophiles can be utilised under acidic
conditions without unwanted side reactions.
An alternative is to convert the alcohol into a tosylate, which has a much
better leaving group and will react with nucleophiles without the need
for the acid.
