An organic substance formed when a hydroxyl
group is substituted for a hydrogen atom in a hydrocarbon. The type of alcohol
used in alcoholic beverages, ethanol, derives from fermenting sugar with yeast.
After alcohol is ingested, the body converts it to sugar-based fuel. Alcohol
acts as a central nervous system depressant, and it may be part of solutions used as
preservatives, antiseptics, or medications. |
| (Structure of alcohol molecule)
Alcohols Preparation
Alcohols are derived from many types of compounds.
The alcohol hydroxyl can be converted to many other functional groups. This
makes alcohols useful in synthesis.
 |
Ethanol
Ethanol is one of the important alcohols. It is
manufactured on a large scale by two main processes :
a.
From sugars and starch by fermentation.
b.
From petroleum fractions by hydration.
Making ethanol by
fermentation
Man used
this process for thousands of years to make ethanol from sugar and starch.
Yeast is added to sugar or starch and left in a warm place for several days in
the absence of air. The fermentation process is anaerobic, which means it takes
place in the absence of oxygen. Yeast releases biological enzymes, which break
down the sugars and starch into glucose. In the fermentation process, the
enzyme called zymase slowly decomposes the glucose to form ethanol and carbon
dioxide. When the concentration of ethanol formed reaches about 15%, yeast is
killed off and the fermentation stops. Hence, it is impossible to produce pure
ethanol by natural fermentation. The ethanol is then purified by fractional
distillation.
Making ethanol by
hydration
This
process is called catalytic hydration, the direct hydration of ethene. Ethene
is obtained from the cracking of petroleum fractions. An additional reaction
combines ethene with water to produce ethanol. The ethanol produced is
condensed to form a liquid and the unreacted ethene is recycled.
Physical properties of alcohol
1. It is a
liquid at room conditions.
2. It is
colourless.
3. It has a
sharp smell.
4. It is
completely miscible with water.
5. It has a
low boiling point.
6. It is
highly volatile.
Chemical properties of
alcohol
1. Combustion
Ethanol is
a very flammable substance. Complete combustion of ethanol produces carbon
dioxide and water.
2. Oxidation
reaction occurs when a substance combines with oxygen.
3. Dehydration
involves the removal of water from a compound.
Uses
of alcohols
Fossil fuels
- they burn very cleanly, producing only carbon dioxide and water. Ethanol is considered a renewable fuel as it can be made from renewable sources such as sugar cane.
- they burn very cleanly, producing only carbon dioxide and water. Ethanol is considered a renewable fuel as it can be made from renewable sources such as sugar cane.
Perfumes
- ethanol is the least toxic of the alcohols it is used in perfumes to stop the plant and animal extracts from going off.
Solvent
- ethanol is the safest of the alcohols it is often used to dissolve chemicals that are insoluble in water. Examples include perfumes, cosmetic s and vegetable essences such as vanilla extract.
Cleaner
- to get rid of bacteria and oil and also in mouth wash.
Antiseptic
- alcohol is safer for use on the skin, because it works at a lower concentration (65-80 percent)
Sedative
- preparing patients for surgery
- ethanol is the least toxic of the alcohols it is used in perfumes to stop the plant and animal extracts from going off.
Solvent
- ethanol is the safest of the alcohols it is often used to dissolve chemicals that are insoluble in water. Examples include perfumes, cosmetic s and vegetable essences such as vanilla extract.
Cleaner
- to get rid of bacteria and oil and also in mouth wash.
Antiseptic
- alcohol is safer for use on the skin, because it works at a lower concentration (65-80 percent)
 |
| (Antiseptic) |
- preparing patients for surgery
