Alcohols — making and reactions
Alcohols
- An alcohol has the –OH (hydroxyl) functional group.
- It is a versatile, central organic compound.
- It can be made several ways and reacts in many.
Practice
The functional group of an alcohol is:
Alcohols are defined by the hydroxyl (–OH) group.
Making alcohols
- steam + an alkene ($\text{H}_3\text{PO}_4$ catalyst) — electrophilic addition.
- halogenoalkane + NaOH(aq), heat — nucleophilic substitution.
- reduction of an aldehyde/ketone ($\text{NaBH}_4$ or $\text{LiAlH}_4$).
- hydrolysis of an ester (dilute acid or alkali, heat).
Practice
Which reaction makes an alcohol?
NaOH(aq) substitutes the halogen for –OH; adding steam to an alkene or reducing a carbonyl also work.
Reactions of alcohols
- combustion → carbon dioxide + water.
- with sodium → hydrogen + a sodium alkoxide (like water, but slower).
- substitution to a halogenoalkane ($\text{HX}$, $\text{PCl}_5$, $\text{SOCl}_2$).
- dehydration → an alkene (hot $\text{Al}_2\text{O}_3$ or conc. acid).
- ester formation with a carboxylic acid (conc. $\text{H}_2\text{SO}_4$ catalyst).
Practice
An alcohol reacting with sodium metal produces:
Like water, alcohols react with sodium to give hydrogen — but more slowly.
Practice
Dehydrating an alcohol (hot Al₂O₃ or conc. acid) gives:
Dehydration removes water from the alcohol to form an alkene (the reverse of steam addition).
You've got it
Key idea
- alcohols have the –OH group
- made from: steam + alkene, halogenoalkane + NaOH(aq), reduction of aldehyde/ketone, ester hydrolysis
- react by combustion, with sodium (→ H₂), dehydration (→ alkene), and ester formation