We will now deal with two important and typical members of
the Alkanol series namely methanol and ethanol
METHANOL
Methanol, otherwise known as wood spirit
or methyl alcohol, is manufactured by the destructive distillation
of wood in limited supply of air or derived from the refining
of crude oil (Petroleum). It is the first member of the alkanol
series with the molecular formula, CH3OH
Properties
Methanol is a colourless liquid with a boiling point
of 65° C (149° F).
It mixes completely with water and with other short-chain
alkanol.
It is very poisonous and toxic if drunk and small quantities
of the alkanol could cause blindness while larger ones,
death.
Methylated spirits consists of ethanol to which about
10 per cent methanol has been added (along with a blue dye
called pyridine) to make it undrinkable.
Reactions of Methanol
The chemical reactions of methanol include:
oxidation to methanal and then methanoic acid;
CH3OH + [O] -------->HCHO + [O] -------> HCOOH
Nucleophilic substitution reactions in which the -OH
group is replaced by another atom or group (such as a halogen);
Formation of esters with alkanoic acids;
CH3OH + HCOOH--->HCOOCH3 + H2O
and
Formation of ethers.
Uses
Methanol is used as a solvent,
a fuel and additive for vehicle fuels, and
to make methanal, from which plastics such as Bakelite
are made
ETHANOL
Sometimes called ethyl alcohol, Ethanol
has the molecular formula C2H5OH. Often when the layman calls
a substance alcohol, ethanol is being referred to. This is because
ethanol, though the second member, is the most typical of the
properties of alkanols (or alcohols).
Laboratory Preparation
Ethanol could be prepared in the laboratory by the hydrolysis
of ethane. This is done by passing a mixture of ethane and steam
over H2SO4 acid serving as catalyst at a temperature of above
500oC and pressure of 100 atm.
C2H4 (g) + H2O(l) -------> C2H5OH(l)
Preparation by Fermentation
Fermentation is the slow breaking down of large molecules of
starch to smaller molecules of alcohol by the enzymatic action
of micro-organisms (usually yeast).
Ethanol can be prepared by extracting starch granules obtained by crushing starchy foodstuffs and then leaving it for some hours after inoculating with suitable enzymes(also found in yeasts).
The following reactions will take place with the gradual conversion of the starch to ethanol:
Starch is hydrolyzed to maltase by the action of diastase (also called invertase)
In the second reaction, maltose is hydrolyzed, by the action of maltase to glucose
Lastly, glucose is converted to ethanol with carbon (IV) oxide gas given off by zymase enzyme
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