Alcohols are the family of organic compounds that have the OH– functional group.
They have the general formula: CNH2N+1OH
The names of all alcohols end with the suffix- ‘ol’ (for example: methanol, ethanol, propanol and so on).
The alcohol used in the brewing industries for consumption is ethanol.
The first five members of the alcohols are neutral, colourless liquids that don’t conduct electricity.
Ethanol is formed by two methods:
|Fermentation||Addition reaction (where steam is added)|
1. A solution of glucose is prepared
2. Yeast is added to the glucose solution
3. Enzymes in yeast break down glucose to ethanol and carbon dioxide
4. When the volume of ethanol in the mixture reaches to 15%, the reaction stops automatically
5. This is because either the glucose has been completely consumed OR the ethanol produced has poisoned and killed the yeast.
6. The solution is distilled to get concentrated ethanol.
|The conditions required:
1. 3000C temperature
2. Phosphoric acid catalyst
3. 60 atm pressure
1. Ethene is made to react with steam at the conditions stated above.
2. This results in the formation of ethanol
Relatively cheaper than addition of steam
|Ethanol of low purity produced
Relatively slower than addition of steam
Batch process- which again slows down rate of production
|Addition||Ethanol of high purity produced
Ethanol produced at a faster rate
Continuous process- boosting rate of production
The reactions of ethanol
Combustion of ethanol
Ethanol burns exothermically with a clear flame. These properties of ethanol have made their debut for the following uses:
Ethanol is mixed with methanol to give methylated spirits which are used in spirit lamps and stoves.
In countries like Brazil, ethanol is being used as a fuel for cars and vehicles too!
Oxidation of ethanol
Leave a bottle of wine without its cork and you’ll notice that the wine goes ‘vinegary’ (sour). This is called as oxidation.
The same but more powerful effect can be achieved by using warm acidified potassium manganate (VII).
In the case above, the colour of the potassium manganate (VII) solution changes from purple to colourless.
Dehydration of ethanol
Ethene is hydrated to produce ethanol. In the same way, dehydration can transform ethanol to ethene.
- Ethanol vapour is passed over a heated catalyst.
- The catalyst can be either aluminium oxide or broken pieces of porous pot.
- Ethene is not soluble in water; it can be collected over water using a downward delivery tube.
Esters are sweet smelling oily liquids. They are used in food flavourings and in perfumes.
Esters form by esterification when an alcohol reacts with an organic acid (such as a carboxylic acid).
For this reaction, a catalyst of concentrated sulphuric acid is used.
Uses and industrial importance of alcohols
Ethanol is the major ingredient in the brewing industry and is used to make brandy, whisky, vodka and other drinks.
Ethanol is also used as a fuel, as an organic solvent in perfumes and to make esters.