Alcohols

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

Ethanol is formed by two methods:

Fermentation Addition reaction (where steam is added)
The process:

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

The process:

1.    Ethene is made to react with steam at the conditions stated above.

2.    This results in the formation of ethanol

 

  Advantages Disadvantages
Fermentation Renewable resource

Sustainable resource

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

Non-renewable

Expensive

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.

The method:

  1. Ethanol vapour is passed over a heated catalyst.
  2. The catalyst can be either aluminium oxide or broken pieces of porous pot.
  3. Ethene is not soluble in water; it can be collected over water using a downward delivery tube.

Esterification

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.

 

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