Ethanol is a straight-chain alcohol, and its molecular formula is C2H5OH. Its empirical formula is C2H6O. An alternative notation is CH3-CH2-OH, which indicates that the carbon of a methyl group (CH3-) is attached to the carbon of a methylene group (-CH2-), which is attached to the oxygen of a hydroxyl group (-OH). It is a constitutional isomer of dimethyl ether. Ethanol is often abbreviated as EtOH, using the common organic chemistry notation of representing the ethyl group (C2H5) with Et.
[edit] Acid-base chemistry
Ethanol's hydroxyl group causes the molecule to be slightly basic. It is almost neutral like water. The pH of 100% ethanol is 7.33, compared to 7.00 for pure water. Ethanol can be quantitatively converted to its conjugate base, the ethoxide ion (CH3CH2O−), by reaction with an alkali metal such as sodium:[11]
2CH3CH2OH + 2Na → 2CH3CH2ONa + H2,
or a very strong base such as sodium hydride:
CH3CH2OH + NaH → CH3CH2ONa + H2.
This reaction is not possible in an aqueous solution, as water is more acidic, so that hydroxide is preferred over ethoxide formation.
[edit] Halogenation
Ethanol reacts with hydrogen halides to produce ethyl halides such as ethyl chloride and ethyl bromide:
CH3CH2OH + HCl → CH3CH2Cl + H2O
HCl reaction requires a catalyst such as zinc chloride.[19] Hydrogen chloride in the presence of their respective zinc chloride is known as Lucas reagent.[11][19]
CH3CH2OH + HBr → CH3CH2Br + H2O
HBr requires refluxing with a sulfuric acid catalyst.[19]
Ethyl halides can also be produced by reacting ethanol with more specialized halogenating agents, such as thionyl chloride for preparing ethyl chloride, or phosphorus tribromide for preparing ethyl bromide.[11][19]
CH3CH2OH + SOCl2 → CH3CH2Cl + SO2 + HCl
[edit] Ester formation
Under acid-catalyzed conditions, ethanol reacts with carboxylic acids to produce ethyl esters and water:
RCOOH + HOCH2CH3 → RCOOCH2CH3 + H2O.
For this reaction to produce useful yields it is necessary to remove water from the reaction mixture as it is formed.
Ethanol can also form esters with inorganic acids. Diethyl sulfate and triethyl phosphate, prepared by reacting ethanol with sulfuric and phosphoric acid respectively, are both useful ethylating agents in organic synthesis. Ethyl nitrite, prepared from the reaction of ethanol with sodium nitrite and sulfuric acid, was formerly a widely-used diuretic.
[edit] Dehydration
Strong acid desiccants, such as sulfuric acid, cause ethanol's dehydration to form either diethyl ether or ethylene:
2 CH3CH2OH → CH3CH2OCH2CH3 + H2O
CH3CH2OH → H2C=CH2 + H2O
Which product, diethyl ether or ethylene, predominates depends on the precise reaction conditions
[edit] Oxidation
Ethanol can be oxidized to acetaldehyde, and further oxidized to acetic acid. In the human body, these oxidation reactions are catalyzed by enzymes. In the laboratory, aqueous solutions of strong oxidizing agents, such as chromic acid or potassium permanganate, oxidize ethanol to acetic acid, and it is difficult to stop the reaction at acetaldehyde at high yield. Ethanol can be oxidized to acetaldehyde, without over oxidation to acetic acid, by reacting it with pyridinium chromic chloride.[19]
The direct oxidation of ethanol to acetic acid using chromic acid is given below.
C2H5OH + 2[O] → CH3COOH + H2O
The oxidation product of ethanol, acetic acid, is spent as nutrient by the human body as acetyl CoA, where the acetyl group can be spent as energy or used for biosynthesis.
[edit] Chlorination
When exposed to chlorine, ethanol is both oxidized and its alpha carbon chlorinated to form the compound, chloral.
4Cl2 + C2H5OH → CCl3CHO + 5HCl
[edit] Combustion
Combustion of ethanol forms carbon dioxide and water:
C2H5OH(g) + 3 O2(g) → 2 CO2(g) + 3 H2O(l); (ΔHr = −1409 kJ/mol[20])