Grades of ethanol
[edit]
Further information: Denatured alcohol
Pure ethanol and alcoholic beverages are heavily taxed as psychoactive drugs, but ethanol has many
uses that do not involve its consumption. To relieve the tax burden on these uses, most jurisdictions
waive the tax when an agent has been added to the ethanol to render it unfit to drink. These
include bittering agents such as denatonium benzoate and toxins such as methanol, naphtha, and
pyridine. Products of this kind are called denatured alcohol.[124][125]
Absolute or anhydrous alcohol refers to ethanol with a low water content. There are various grades
with maximum water contents ranging from 1% to a few parts per million (ppm). If azeotropic
distillation is used to remove water, it will contain trace amounts of the material separation agent
(e.g. benzene).[126] Absolute alcohol is not intended for human consumption. Absolute ethanol is used
as a solvent for laboratory and industrial applications, where water will react with other chemicals,
and as fuel alcohol. Spectroscopic ethanol is an absolute ethanol with a low absorbance
in ultraviolet and visible light, fit for use as a solvent in ultraviolet-visible spectroscopy.[127] Pure
ethanol is classed as 200 proof in the US, equivalent to 175 degrees proof in the UK system.
[128]
Rectified spirit, an azeotropic composition of 96% ethanol containing 4% water, is used instead of
anhydrous ethanol for various purposes. Spirits of wine are about 94% ethanol (188 proof). The
impurities are different from those in 95% (190 proof) laboratory ethanol.[129]
Reactions
[edit]
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Further information: Alcohol (chemistry)
Ethanol is classified as a primary alcohol, meaning that the carbon that its hydroxyl group attaches to
has at least two hydrogen atoms attached to it as well. Many ethanol reactions occur at its hydroxyl
group.
Ester formation
[edit]
In the presence of acid catalysts, ethanol reacts with carboxylic acids to produce ethyl esters and
water:
RCOOH + HOCH2CH3 → RCOOCH2CH3 + H2O
This reaction, which is conducted on large scale industrially, requires the removal of the water from
the reaction mixture as it is formed. Esters react in the presence of an acid or base to give back the
alcohol and a salt. This reaction is known as saponification because it is used in the preparation of
soap. Ethanol can also form esters with inorganic acids. Diethyl sulfate and triethyl phosphate are
prepared by treating ethanol with sulfur trioxide and phosphorus pentoxide respectively. Diethyl
sulfate is a useful ethylating agent in organic synthesis. Ethyl nitrite, prepared from the reaction of
ethanol with sodium nitrite and sulfuric acid, was formerly used as a diuretic.
Dehydration
[edit]
In the presence of acid catalysts, alcohols can be converted to alkenes such as ethanol to ethylene.
Typically solid acids such as alumina are used.[130]
CH3CH2OH → H2C=CH2 + H2O
Since water is removed from the same molecule, the reaction is known as intramolecular dehydration.
Intramolecular dehydration of an alcohol requires a high temperature and the presence of an acid
catalyst such as sulfuric acid.[131] Ethylene produced from sugar-derived ethanol (primarily in Brazil)
competes with ethylene produced from petrochemical feedstocks such as naphtha and ethane.[citation
needed]
At a lower temperature than that of intramolecular dehydration, intermolecular alcohol
dehydration may occur producing a symmetrical ether. This is a condensation reaction. In the
following example, diethyl ether is produced from ethanol:
