Chemistry, Third edition

ALCOHOLS 333

Dilute aqueous solutions of ethanol, when drunk as beverages, cause a pleasant

relaxed feeling; however, too much ‘alcohol’ leads to headaches and vomiting. Long-

term abuse of ethanol can lead to liver damage.

Methanol

Originally, methanol was produced when wood was distilled and, for this reason,

was known as wood alcohol. Today, methanol can be produced from the catalytic

hydrogenation of carbon monoxide:

CO(g)2H 2 (g)CH 3 OH(l)

Methanol is used as a solvent and as an antifreeze for car radiators. It is much more

toxic than ethanol – drinking methanol can lead to blindness and then to death.

Methanol can be used as fuel for cars.

Methylated spirits

Alcoholic beverages are heavily taxed in many countries, but besides being used to

make drinks, ethanol has many useful industrial applications. It is used to make

other organic chemicals and is an extremely useful industrial solvent. In order to

avoid heavy taxation of the ethanol used for industrial purposes it is rendered unfit

to drink (denatured). Small amounts of methanol are added to ethanol to produce

‘industrial methylated spirit’. A purple dye is often added to methylated spirit sold

for domestic use. The dye serves as a warning that the mixture is undrinkable.

Chemical properties of alcohols

1.They burn in air, giving out heat, and can be used as fuels:

C 2 H 5 OH(l)3O 2 (g)2CO 2 (g)3H 2 O(l)

2.Alcohols can be oxidized to carboxylic acids. For example, ethanol is slowly oxi-

dized to ethanoic acid (acetic acidfound in vinegar) by bacteria present in the air.

This is why an open bottle of wine tastes sour when left in the air for a few days.

bacteria

C 2 H 5 OH(l)O 2 (g) ——CH 3 COOH(l)H 2 O(l)

Strong oxidizing agents, such as acid potassium permanganate (manganate(VII))

solution or chromic acid (acidified sodium dichromate(VI) solution) will also

oxidize alcohols.

3.Alcohols react with carboxylic acids to make esters(see some reactions of car-

boxylic acids page 339).

Primary, secondary and tertiary alcohols

Apart from methanol, alcohols may be classified as primary, secondary or tertiary:

primary alcohols contain a —CH 2 OH group

secondary alcohols contain aCHOH group

tertiary alcohols contain a —COH group

Primary, secondary

and tertiary

alcohols

Classify the isomers of

pentanol in Exercise 18B(i)

as primary, secondary or

tertiary.

Exercise 18D