Alkanols and Hydrohalic Acids (HX) Chemistry Tutorial
- Alkanols belong to a class of organic compounds known as alcohols, compounds that contain the hydroxyl functional group (OH).
- The active site on an alkanol molecule is the hydroxyl (OH) functional group.
- The halide ion (X-) from a concentrated solution of a strong hydrohalic acid (HX(aq)) can replace the hydroxyl functional group to produce a haloalkane (alkyl halide or halogenoalkane) in a substitution reaction.(1)
- The general chemical equation for this substitution reaction is:
general word equation alkanol + hydrohalic acid → haloalkane + water general molecular equation R−OH + HX → R−X + H2O
R is a hydrocarbon chain (an alkane chain which is the parent hydrocarbon).
X is a halogen atom: chlorine, bromine or iodine.
- Reaction with concentrated HBr and HI : All alkanols (primary, secondary and tertiary) readily react at room temperature with HI or HBr
- Reaction with concentrated HCl :
⚛ Tertiary alkanols readily react with HCl and room temperature
⚛ Secondary alkanols react with HCl at room temperature in the presence of a suitable catalyst.
⚛ Primary alkanols react with HCl only when heated in the presence of a suitable catalyst.