Methanol, CH3OH, (i.e. methyl alcohol) is the simplest
aliphatic alcohol, and is the first member of the homologous series.
Methanol is a colourless liquid, completely miscible with
water and organic solvents and is very hydroscopic.
Methanol has an agreeable odour, and a burning taste.
Methanol is a potent nerve poison.
Methanol has the physical properties
- Melting Point : -97 degC
- Boiling Point : 65 deg0C
- Relative Density : 0.8
Manufacture of Methanol
Methanol is made by a method different from that used
in the preparation of the other alcohol. The naphtha fraction
from the distillation of crude petroleum, is used as
a raw material for the manufacture of methanol. When naphtha
is reacted with a high steam ratio, under pressure and
at high temperature, synthesis gas of low methane content is
obtained. Most of the carbon from the naphtha is
converted to carbon monoxide and carbon dioxide which can be
removed from the gaseous mixture to leave hydrogen of high purity.
C + H2O ==> CO + H2
When a mixture of hydrogen and carbon monoxide in the
ratio 2:1 is passed over a catalyst (e.g. a mixture
of zinc oxide and chromium oxide) under high pressure
and at high temperature, methanol is formed.
CO + 2H2 ==> CH3OH
Chemical Properties of Methanol
- Combustion of Methanol
- Methanol burns with a pale-blue, non-luminous flame to
form carbon dioxide and steam.
2CH3OH + 302 ==> 2CO2 + 4H2O
- Oxidation of Methanol
- Methanol is oxidised
to form formaldehyde.
- with acidified Potassium Dichromate, K2Cr2O7, or
- with acidified Sodium Dichromate, Na2Cr2O7, or
- with acidified Potassium Permanganate, KMnO4,
CH3OH ==> H.CHO + H2O
If the oxidising agent is in excess, the formaldehyde is
further oxidised to formic acid and then to carbon dioxide and water.
H.CHO ==> H.COOH ==> CO2 + H2O
- Catalytic Oxidation of Methanol
- The catalytic oxidation of methanol using platinum
wire is of interest as it is used in model aircraft engines
to replace the sparking plug arrangement of the conventional
petrol engine. The heat of reaction is sufficient to spark
- Dehydrogenation of Methanol
- Methanol can also be oxidised to formaldehyde by passing
its vapour over copper heated to 300 degC. Two atoms of
hydrogen are eliminated from each molecule to form hydrogen
gas and hence this process is termed dehydrogenation.
CH3OH ==> H.CHO + H2
- Dehydration of Methanol
- Methanol does not undergo dehydration reactions. Instead, in
reaction with sulphuric acid the ester, dimethyl sulphate
2 CH3OH ==> (CH3)2SO4 + H2O
Methanol Dimethyl Water
- Esterification of Methanol
- Methanol reacts with organic acids to form esters.
CH3OH + H.COOH ==> H.COO.CH3 + H2O
Methanol Formic Methyl Water
- Substitution of Methanol with Sodium
- Methanol reacts with sodium at room temperature to
liberate hydrogen. This reaction is similar to the reaction of
sodium with ethanol.
2 CH3OH + 2 Na ==> 2CH3ONa + H2
Methanol Sodium Sodium Hydrogen
- Substitution of Methanol with Phosphorus Pentachloride
- Methanol reacts with phosphorus pentachloride at room
temperature to form hydrogen chloride, methyl chloride,
(i.e. chloroethane) and phosphoryl chloride.
CH3OH + PCl5 ==> HCl + CH3Cl + POCl3
Methanol Phosphorus Hydrogen Methyl Phosphoryl
Pentachloride Chloride Chloride Chloride
- Substitution of Methanol with Hydrogen Chloride
- Methanol reacts with hydrogen chloride to form
methyl chloride (i.e. chloromethane) and water. A dehydrating
agent (e.g. zinc chloride) is used.
CH3OH + HCl ==> CH3Cl + H2O
Uses of Methanol
Methanol is an important industrial material and it is used
- in the manufacture of formaldehyde,
- as a solvent in the paint and varnish industry, and
- as an anti-Freeze in car radiators.
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