Ethanol, C2H5OH, (also called Ethyl Alcohol) is the second member of the aliphatic alcohol series. It is a clear colourless liquid with a pleasant smell. Except for alcoholic beverages, nearly all the ethanol used industrially is a mixture of 95% ethanol and 5% water, which is known simply as 95% alcohol. Although pure ethyl alcohol (known as absolute alcohol) is available, it is much more expensive and is used only when definitely required.
C2H4 + H2O ==> C2H5OH Ethene Steam Ethanol
invertase C12H22O11 + H2O ==> C6H12O6 + C6H12O6 Sucrose Glucose Fructose
zymase C6H12O6 ==> 2C2H5OH + 2CO2 Ethanol
The fermentation process takes three days and is carried out at a temperature between 250C and 300C. The ethanol is then obtained by fractional distillation.
Although the boiling point of ethanol, 78.3 degC, is significantly lower than the boiling point of water, 100 degC, these material cannot be separated completely by distillation. Instead, an azeotropic mixture (i.e. a mixture of 95% ethanol and 5% water) is obtained, and the boiling point of the azeotrope is 78.15oC. In a distillation, the most volatile material (i.e. the material that has the lowest boiling point) is the first material to distill from the distillation flask, and this material is the azeotrope of 95% ethanol which has the lowest boiling point. If an efficient fractionating column is used, there is obtained first 95% alcohol, then a small intermediate fraction of lower concentration, and then water. But no matter how efficient the fractionating column used, 95% alcohol cannot be further concentrated by distillation.
The separation of a mixture by fractional distillation occurs because the vapour has a different composition from the liquid from which it distils (i.e. the vapour is richer in the more volatile component). We cannot separate 95% alcohol into its components by distillation, because here the vapour has exactly the same composition as the liquid; towards distillation, then, 95% alcohol behaves exactly like a pure compound.
A liquid mixture that has the peculiar property of giving a vapour of the same composition is called an azeotrope (i.e. a constant-boiling mixture). Since it contains two components 95% alcohol is a binary azeotrope. Most azeotropes, like 95% alcohol, have boiling points lower than those of their components, and are known as minimum-boiling mixtures. Azeotropes having boiling points higher than those of their components are known as maximum-boiling mixtures.
Melting Point -1150C Boiling Point 780C Specific Gravity 0.79.
C2H5OH + 3O2 ==> 2CO2 + 3H2O Ethanol
[O] C2H5OH ==> CH3CHO + H2O Ethanol Ethanal
The ethanal is further oxidised to ethanoic acid (i.e. acetic acid) if the oxidising agent is in excess.
[O] CH3CHO ==> CH3COOH Ethanal Ethanoic Acid
The oxidising agent usually used for this reaction is a mixture of sodium dichromate or potassium dichromate and sulphuric acid which react together to provide oxygen atoms as follows.
Na2Cr2O7 + 4 H2SO4 ==> Na2SO4 + Cr2(SO4)3 + 4H2O + 3[O]
H2SO4 C2H5OH ==> C2H4 + H2O 170 degC
When ethanol is mixed with concentrated sulphuric acid with the alcohol in excess and heated to 140 degC, diethyl ether distils over (two moles of ethanol loses one mole of water) .
H2SO4 2 C2H5OH ==> C2H5OC2H5 + H2O 140 deg
C2H5OH + Na ==> C2H5ONa + (H2(
Apart from this reaction, ethanol and the other alcohols show no acidic properties.
C2H5OH ==> CH3CHO + H2 Ethanol Ethanal
H(+) C2H5OH + CH3COOH ==> CH3COOC2H5 + H2O Ethanol Ethanoic Ethyl Water Acid Acetate
C2H5OH + PCl5 ==> C2H5Cl + POCl3 + HCl Ethanol Phosphorus Ethyl Phosphorus Hydrogen Pentachloride Chloride Pentachloride Chloride
ZnCl2 C2H5OH + HCl ==> C2H5Cl + H2O Ethanol Ethyl Chloride