Ethanol and sulfuric acid can react in three ways: esterification, dehydration with one molecule of each resulting in a gas, and dehydration with two molecules resulting in a liquid anesthetic. Sulfuric acid is a strong acid and dehydrating agent that can ionize itself and remove hydrogen and oxygen atoms from molecules. Ethanol is similar to water and can produce ethyl hydrogen sulfate and diethyl sulfate through esterification. Dehydration can result in ethylene gas or diethyl ether liquid. The product depends on the reaction conditions and the amount of each reactant present.
The connection between ethanol and sulfuric acid involves at least three possible reaction routes. They are esterification, which involves one or two molecules of ethanol or alcohol, and dehydration, which again involves one or two molecules of alcohol. If the dehydration involves only one molecule each of ethanol and sulfuric acid, the product is a gas, important in nature and useful in the laboratory and in industry. When two alcohol molecules are joined by dehydration, the result is a liquid of historical medical significance. Both esterification products are of limited use.
Sulfuric acid is not only a very strong acid, it is also an outstanding dehydrating agent. It is such a strong acid that it can ionize itself, even without water, while as a dehydrator it can “rip” hydrogen and oxygen atoms from molecules to satisfy its “thirst”. The latter feature is demonstrated through the simple high school experiment in which a few grains of table sugar, C12H22O11, are combined with a few drops of concentrated sulfuric acid in a test tube or beaker. Within seconds, the reagents turn pitch black and bubble violently. The black color is due to the now elementary 12 carbon atoms of each sugar molecule, while the 22 hydrogen atoms and 11 oxygen atoms that have been removed have been transformed into 11 water molecules.
Ethanol, also called grain alcohol or grain alcohol, is very similar to water. Its structure is CH3CH2OH. Basically, ethanol is simply water, with one of its hydrogen atoms replaced by a carbon-based handle, the relatively inert CH3CH2-. Another way to think of ethanol is as a very weak base, similar, at least superficially, to sodium hydroxide, NaOH. Although ethanol is normally too weak a base to be ionised, under certain conditions it should be capable of producing salt-like structures.
Sodium hydroxide can produce one of two salts with sulfuric acid, one of which is sodium hydrogen sulfide (NaHSO4), derived from one base and one acid molecule. Although it is a salt, it is also an acid, as it still retains a hydrogen atom in its structure. If this acidic salt is reacted with a second molecule of NaOH, a neutral salt is obtained: sodium sulfate (Na2SO4). Consequently, if ethanol and sulfuric acid are combined under mild and controlled conditions, ethyl hydrogen sulfate results through the reaction route CH3CH2OH+H2SO4→CH3CH2OSO3H, while if this acid-ester resulting from the combination of ethanol and sulfuric acid is further reacted with another ethanol molecule, diethyl sulfate is obtained, more simply called ethyl sulfate. Interestingly, although it is of limited use, forensic scientists employ ethyl sulfate to detect alcohol in blood and urine days after it has been consumed.
Under more stringent conditions, esterification is replaced by dehydration. Single molecule dehydration follows the equation CH3CH2OH→CH2=CH2+HOH. The gaseous product is ethylene, a plant hormone associated with fruit ripening and other processes. If two ethanol molecules are dehydrated instead of one, the reaction is 2CH3CH2OH→CH3CH2OCH2CH3+HOH. This reaction results in a historically significant end product: the liquid anesthetic, diethyl ether.
The connection between ethanol and sulfuric acid is therefore at least fourfold. The results of their combination include two esterification products and two dehydration products, depending on the conditions under which the reaction is conducted. In addition to delicate reaction conditions, the product of the esterification depends on the amount of each reactant present at any point during the reaction. Dehydration also depends on the relative populations of ethanol and sulfuric acid at any time during the reaction.
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