The member of the homologous series called Alcohols have names which end in “ol”. Examples are methanol, ethanol and propanol.
Alcohols all contain an -OH functional group attached to a hydrocarbon chain.
Structural formula and displayed formula for methanol:
CH₃-OH
Structural formula and displayed formula for ethanol:
CH₃-CH₂-OH (or simply C₂H₅OH)
Structural formula and displayed formula for propan-1-ol:
CH₃-CH₂-CH₂-OH
Structural formula and displayed formula for butan-1-ol:
CH₃-CH₂-CH₂-CH₂-OH
1) Ethanol can be oxidised by complete combustion. With excess oxygen the complete combustion of ethanol (C₂H₅OH) in air produces carbon dioxide and water:
C₂H₅OH (l) + 3O₂ (g) → 2CO₂ (g) + 3H₂O (l)
2) Ethanol can be oxidised in air in the presence of microorganisms (‘microbial oxidation’) to form ethanoic acid (CH₃COOH).
3) Ethanol can be oxidised by heating with the oxidising agent potassium dichromate(VI) (K₂Cr₂O₇) in dilute sulfuric acid (H₂SO₄).
In the equation below, [O] means oxygen from an oxidising agent.
CH₃CH₂OH + 2[O] → CH₃COOH + H₂O
This mixture starts orange but when the reaction happens turns green which indicates the presence of Cr³⁺ ions which are formed when the potassium dichromate(VI) is reduced.
In the hydration of ethene, ethanol is made by passing ethene and steam over a catalyst.
Water is added to ethene, this is known as hydration.
Conditions
Catalyst: Phosphoric acid (H3PO4)
Temperature: 300°C
Pressure: 60 atm
Fermentation is the conversion of sugar, e.g. glucose into ethanol by enzymes from yeast.
Conditions
Catalyst: Zymase (enzyme found in yeast)
Temperature: 30°C – The process is carried out at low temperatures as not to denature the enzymes.
Other: Anaerobic (no oxygen present) – if oxygen were present, the yeast produce carbon dioxide and water instead of ethanol.
In the production of ethanol the process of fermentation is carried out at a low temperature (30⁰-40⁰).
Above 40⁰ the enzymes would permanently lose their structure (denature).
At a temperature lower than 30⁰ the process would be too slow.
Fermentation is conducted in the absence of air. In the presence of air (aerobic conditions), enzymes in the yeast produce carbon dioxide and water instead of ethanol.
Also, in the presence of air, the ethanol can oxidise to ethanoic acid.