Chemistry Some Commercially Important Alcohols

Topics Covered :

● Some Commercially Important Alcohols
● Methanol
● Ethanol

Some Commercially Important Alcohols :

Methanol and ethanol are among the two commercially important alcohols.

Methanol :

`=>` Methanol, `color{red}(CH_3OH)`, also known as `color{green}("wood spirit")`, was produced by destructive distillation of wood.

`=>` Now a days, most of the methanol is produced by catalytic hydrogenation of carbon monoxide at high pressure and temperature and in the presence of `color{red}(ZnO – Cr_2O_3)` catalyst.

`color{red}(CO +2H_2 underset(200-300 atm 573-673 K) overset(ZnO - Cr_2O_3)→ CH_3OH)`

`=>` Methanol is a colourless liquid and boils at `337 K`.

`=>` It is highly poisonous in nature.

`=>` Ingestion of even small quantities of methanol can cause blindness and large quantities causes even death.

`=>` Methanol is used as a solvent in paints, varnishes and chiefly for making formaldehyde.

Ethanol :

`=>` Ethanol, `color{red}(C_2H_5OH)`, is obtained commercially by fermentation, the oldest method is from sugars.

● The sugar in molasses, sugarcane or fruits such as grapes is converted to glucose and fructose, (both of which have the formula `color{red}(C_6H_(12)O_6)`), in the presence of an enzyme, invertase.

● Glucose and fructose undergo fermentation in the presence of another enzyme, zymase, which is found in yeast.

`color{red}(C_(12)H_(22)O_(11) +H_2O oversettext(Invertase)→ undersettext(Glucose)(C_6H_(12)O_6)+ undersettext(Fructose)(C_6H_(12)O_6))`

`color{red}(C_6H_(12)O_6 oversettext(Zymase)→ 2C_2H_5OH +2CO_2)`

`=>` In wine making, grapes are the source of sugars and yeast.

● As grapes ripen, the quantity of sugar increases and yeast grows on the outer skin.

● When grapes are crushed, sugar and the enzyme come in contact and fermentation starts.

● Fermentation takes place in anaerobic conditions i.e. in absence of air.

● Carbon dioxide is released during fermentation.

● The action of zymase is inhibited once the percentage of alcohol formed exceeds `14` percent.

● If air gets into fermentation mixture, the oxygen of air oxidises ethanol to ethanoic acid which in turn destroys the taste of alcoholic drinks.

`=>` Ethanol is a colourless liquid with boiling point `351 K`.

`=>` It is used as a solvent in paint industry and in the preparation of a number of carbon compounds.

`=>` The commercial alcohol is made unfit for drinking by mixing in it some copper sulphate (to give it a colour) and pyridine (a foul smelling liquid). It is known as `color{green}("denaturation of alcohol")`.

`=>` At present, large quantities of ethanol are obtained by hydration of ethene.