Introduction to Alkanols
Alkanols are often referred to as alcohols. They can be used to fuel cars as they are flammable. Unlike alkanes, alkenes and alkynes, alkanols are not hydrocarbons as, in addition to carbon and hydrogen atoms, they contain oxygen atoms.
Structure of Alkanols
Alkanols are similar in structure to alkanes, however one hydrogen has been replaced by an OH (hydroxyl) group.
For example, the alkanol most people refer to as 'alcohol' is the alkanol that contains two carbon atoms (ethanol). This has a similar structural formula to ethane, but one of the hydrogens has been replaced by a hydroxyl group. This is shown below.H H | | H - C - C - H | | H OH
As shown in the example above, alkanols are named in a similar way to alkanes. However, the ane is replaced with anol.
However, if the alkanol contains three or more carbon atoms in the longest carbon chain, the number of the carbon to which the OH group is attached must be given. The carbon atom numbering system is the same as that of alkenes when the carbon number that is double bonded to another carbon atom must be given. Therefore, butan-2-ol is the alkanol that contains four carbon atoms and has the OH group on the second carbon along from the end of the carbon chain.
Reactions of Alkanols
- Alkanols are flammable and burn in excess oxygen to form carbon dioxide and water. For example, shown below is the equation for when ethanol burns in air.
- Alkanols react with sodium (Na) to produce sodium alkoxide and hydrogen gas. For example, shown below is the equation of the reaction between methanol and sodium. It should be noted that with an increased number of carbon atoms in the longest carbon chain, alkanols become less reactive and less soluble in water.
- A primary alkanol (one in which the OH group is attached to carbon-1) can be oxidised to form an alkanoic acid. For example, methanol can be oxidised to methanoic acid. Note that water is also produced in this reaction.
C2H5OH (l) + 3O2 (g)→ 2CO2 (g) + 3H2O (l)
2Na (s) + 2CH3OH (l)→ 2Na+OCH3- (aq) + H2 (g)