The alcohols are another homologous series of compounds that have the general formula CnH2n+1OH.
Types of Alcohol
We have three different types of alcohol depending on the structure, the different types will reaction differently which is why you need to know the differences, but they are very simple.
The easy way to work it out is the number of carbon atoms bonded to the COH group. A primary alcohol has 0 or 1 carbon on the COH. The secondary alcohol has 2 carbons and the tertiary alcohols have got 3 carbon atoms bonded to the C-OH.
And now we come to tertiary alcohol; these will not be oxidised very easily so not very much will happed.
There are two methods of manufacturing ethanol, either from ethene or sugar.
Producing it from ethene is more common in developed countries like those in North America and Europe where ethene is widely available. The following reaction between ethene and steam takes place with a phosphoric acid catalyst at 600°C and high pressure.
The production of ethanol using sugar is more common in developing nations with less oil and ethene but alot of agricultural produce. This method also can make use of material that would have otherwise gone to waste.
Plant material is fermented for several days, and the following reaction takes place:
Gluscose Ethanol + Carbon Dioxide
C6H12O6 (aq) 2C2H5OH (aq) + 2CO2 (g)
The ethanol produced is combustible so can be used in car engines. This has become known as biofuel, and it was originally thought to provide a more environmentally friendly source of fuel to replace fossil fuels. However it appears to do more harm than good by reducing the supply of food and encouraging deforestation to plant crops that can be fermented.
Ethanol is by far the most commonly used alcohol, and has numerous applications, including:
It is used as fuel. Most notably in Brazil, where either pure ethanol or a mix with petrol is used to fuel the majority of cars. This can be a carbon neutral way to fuel transport (see above) because, although carbon dioxide is produced in combustion, manufacturing it by fermentation means all CO2 is absorbed by growing the plants to ferment.
Alcohols can be oxidised by using chemicals like acidified potassium dichromate in warm conditions. The products vary depending on the type of alcohol.
A primary alcohol will oxidise to to an aldehyde and given further oxidation it will become a carboxylic acid. Have a look at the example below using ethanol.
The [O] is notation used to represent oxidation. Ethanol first becomes the aldehyde ethanal and produces water. And then with further oxidation (step 2) this is oxidised to ethanoic acid.
A secondary alcohol can will be oxidised to a ketone with the functional group CO; the diagram below shows what the ketone propanone looks like.
Formerly known as acetic acid, it is a type of carboxylic acid with the molecular formula of C2H4O2 and structural formula of:
It is the acid in vinegar, and so if a wine is left, the ethanol in it oxidises to become ethanoic acid:
Ethanol + Oxygen ® Ethanoic Acid + Water
C2H5OH + O2 ® CH3COOH + H2O