Alcohols Organic Chemistry

 Alcohols are one of the most important organic compounds

The alcohols are a homologous series of organic compounds. They all contain the functional group –OH, which is responsible for the properties of alcohols.

The names of alcohols end with ‘ol’, eg ethanol.

The first three alcohols in the homologous series are methanol, ethanol and propanol. They are highly flammable, making them useful as fuels. They are also used as solvents in marker pens, medicines, and cosmetics (such as deodorants and perfumes).

Ethanol is the alcohol found in alcoholic drinks such as wine and beer.

let's see these tiny videos about them

General Formula of alcohols

Preparation of alcohols (summary)

See this nice video about method one for preparation : Fermentation of sugars

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Conditions of fermentation:

1. Yeast, a microorganism that produces biological catalyst or enzyme.)

2. Optimum temperature of 25 - 35°C

3. Absence of oxygen (Air-lock system or anaerobic conditions)

To prevent oxidation of ethanol to ethanoic acid or vinegar that has a sour taste.

4. Pressure conditions:

 In a pressurized container.

 CO2 (g) will dissolve in the solution when the pressure is high.

 When the container is opened, the pressure decreases as the gas escapes. Thus, the liquid will fizz (as the container is opened due to CO2 escaping).

The concentration of ethanol in the mixture is 10 – 15 %. At a higher concentration of ethanol, the yeast cells are killed.

 How is ethanol concentrated? By fractional distillation until it is a 95% solution.

Q: Why does the fermentation process stop?

When the sugar has all been converted to ethanol or insufficient yeast remains to carry on the sugar conversion.

At the end of fermentation process, pure alcohol is extracted by fractional distillation. The mixture is boiled and the alcohol vapor reaches the top of the fractionating column where it condenses into a liquid.

Advantages of this method over industrial method: it uses renewable sources

Comparison between the two methods of forming alcohols