Oleum
Encyclopedia
Oleum or fuming sulfuric acid refers to a solution of various compositions of sulfur trioxide
in sulfuric acid
or sometimes more specifically to disulfuric acid
(also known as pyrosulfuric acid).
Oleums can be described by the formula ySO3.H2O where y is the total molar sulfur trioxide content. The value of y can be varied, to include different oleums.
They can also be described by the formula H2SO4.xSO3 where x is now defined as the molar free sulfur trioxide content. Oleum is generally assayed according to the free SO3 content by weight. It can also be expressed as a percentage of sulfuric acid strength; for oleum concentrations, that would be over 100%. For example, 10% Oleum can also be expressed as H2SO4.0.1SO3, 1.0225SO3.H2O or 102.25% Sulfuric Acid. The conversion between % acid and % oleum is: % Acid = 100 + 18/80 * % Oleum
A value for x of 1 gives us the empirical formula
H2S2O7 for disulfuric (pyrosulfuric) acid. Pure disulfuric acid itself is a solid at room temperature, melting at 36 °C and rarely used either in the laboratory or industrial processes.
, where sulfur
is oxidized to sulfur trioxide
which is subsequently dissolved in concentrated sulfuric acid. Sulfuric acid itself is regenerated by dilution of part of the oleum.
The lead chamber process
for sulfuric acid production was abandoned partly because it could not produce sulfur trioxide or concentrated sulfuric acid directly due to corrosion of the lead, and absorption of NO2 gas. Until this process was made obsolete by the contact process
, oleum had to be obtained through indirect methods. Historically, the biggest production of oleum came from the distillation
of iron sulfate
s at Nordhausen
, from which the historical name Nordhausen sulfuric acid is derived.
of hydration
. When SO3 is added to water, rather than simply dissolving, it tends to form a fine mist of sulfuric acid, which is difficult to manage. However, SO3 added to concentrated sulfuric acid readily dissolves, forming oleum which can then be diluted with water to produce additional concentrated sulfuric acid.
Certain compositions of oleum are solid at room temperature, and thus is safer to ship than when liquid. Solid oleum can then be converted into liquid at the destination through steam heating or dilution or concentration. This requires some care to prevent overheating and evaporation of sulfur trioxide. To extract it from a tank car requires careful heating using steam conduits within the tank car. Great care must be taken to avoid overheating, as this can increase the internal pressure within the tank car to a value exceeding the limit of the tank's safety valve
.
In Richmond, California
in 1993 a significant release occurred due to overheating, causing a release of sulfur trioxide that absorbed moisture from the atmosphere, creating a mist of micrometre-sized sulfuric acid particles that formed an inhalation health hazard. This mist produced adverse health effects on residents and workers over a wide area.
. The first nitration
can occur with nitric acid in sulfuric acid, but this deactivates the ring towards further electrophilic substitution. A stronger reagent, oleum, is needed to introduce the second nitro group onto the aromatic ring.
. The chemical requirements for explosives manufacture often call for anhydrous mixtures containing nitric acid
and sulfuric acid
. Ordinary commercial grade nitric acid consists of the constant boiling azeotrope
of nitric acid and water, and contains 68% nitric acid. Mixtures of ordinary nitric acid in sulfuric acid therefore contain substantial amounts of water and are unsuitable for processes such as occur in the manufacture of trinitrotoluene.
Anhydrous nitric acid, referred to as white fuming nitric acid
, can be used to prepare water-free nitration
mixtures, and this method is used in laboratory scale operations where the cost of material is not of primary importance. Fuming nitric acid is very hazardous to handle and transport, because it is extremely corrosive and volatile. For industrial use, such strong nitration
mixtures are prepared by mixing oleum with ordinary commercial nitric acid so that the free sulfur trioxide in the oleum consumes the water in the nitric acid.
, or virtually any other sugar
, it will draw the elements of water out of the sugar in an exothermic reaction, leaving nearly pure carbon as a solid. This carbon expands outward, hardening as a solid black substance with gas bubbles in it.
Sulfur trioxide
Sulfur trioxide is the chemical compound with the formula SO3. In the gaseous form, this species is a significant pollutant, being the primary agent in acid rain. It is prepared on massive scales as a precursor to sulfuric acid.-Structure and bonding:Gaseous SO3 is a trigonal planar molecule of...
in sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
or sometimes more specifically to disulfuric acid
Disulfuric acid
Disulfuric acid is an oxoacid of sulfur. It is a major constituent of fuming sulfuric acid, oleum, and this is how most chemists encounter it. It is also a minor constituent of liquid anhydrous sulfuric acid due to the equilibria:...
(also known as pyrosulfuric acid).
Oleums can be described by the formula ySO3.H2O where y is the total molar sulfur trioxide content. The value of y can be varied, to include different oleums.
They can also be described by the formula H2SO4.xSO3 where x is now defined as the molar free sulfur trioxide content. Oleum is generally assayed according to the free SO3 content by weight. It can also be expressed as a percentage of sulfuric acid strength; for oleum concentrations, that would be over 100%. For example, 10% Oleum can also be expressed as H2SO4.0.1SO3, 1.0225SO3.H2O or 102.25% Sulfuric Acid. The conversion between % acid and % oleum is: % Acid = 100 + 18/80 * % Oleum
A value for x of 1 gives us the empirical formula
Empirical formula
In chemistry, the empirical formula of a chemical compound is the simplest positive integer ratio of atoms of each element present in a compound. An empirical formula makes no reference to isomerism, structure, or absolute number of atoms. The empirical formula is used as standard for most ionic...
H2S2O7 for disulfuric (pyrosulfuric) acid. Pure disulfuric acid itself is a solid at room temperature, melting at 36 °C and rarely used either in the laboratory or industrial processes.
Production
Oleum is produced in the contact processContact process
The contact process is the current method of producing sulphuric acid in the high concentrations needed for industrial processes. Platinum was formerly employed as a catalyst for the reaction, but as it is susceptible to poisoning by arsenic impurities in the sulfur feedstock, vanadium oxide is...
, where sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
is oxidized to sulfur trioxide
Sulfur trioxide
Sulfur trioxide is the chemical compound with the formula SO3. In the gaseous form, this species is a significant pollutant, being the primary agent in acid rain. It is prepared on massive scales as a precursor to sulfuric acid.-Structure and bonding:Gaseous SO3 is a trigonal planar molecule of...
which is subsequently dissolved in concentrated sulfuric acid. Sulfuric acid itself is regenerated by dilution of part of the oleum.
The lead chamber process
Lead chamber process
The lead chamber process was an industrial method used to produce sulfuric acid in large quantities. It has been largely supplanted by the contact process....
for sulfuric acid production was abandoned partly because it could not produce sulfur trioxide or concentrated sulfuric acid directly due to corrosion of the lead, and absorption of NO2 gas. Until this process was made obsolete by the contact process
Contact process
The contact process is the current method of producing sulphuric acid in the high concentrations needed for industrial processes. Platinum was formerly employed as a catalyst for the reaction, but as it is susceptible to poisoning by arsenic impurities in the sulfur feedstock, vanadium oxide is...
, oleum had to be obtained through indirect methods. Historically, the biggest production of oleum came from the distillation
Distillation
Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
of iron sulfate
Iron sulfate
Iron sulfate may refer to:*Ferrous sulphate, Iron sulfate, FeSO4*Ferric sulphate, Iron sulfate, Fe23...
s at Nordhausen
Nordhausen
Nordhausen is a town at the southern edge of the Harz Mountains, in the state of Thuringia, Germany. It is the capital of the district of Nordhausen...
, from which the historical name Nordhausen sulfuric acid is derived.
Sulfuric acid production
Oleum is an important intermediate in the manufacture of sulfuric acid due to its high enthalpyEnthalpy
Enthalpy is a measure of the total energy of a thermodynamic system. It includes the internal energy, which is the energy required to create a system, and the amount of energy required to make room for it by displacing its environment and establishing its volume and pressure.Enthalpy is a...
of hydration
Hydration reaction
In organic chemistry, a hydration reaction is a chemical reaction in which a hydroxyl group and a hydrogen cation are added to the two carbon atoms bonded together in the carbon-carbon double bond which makes up an alkene functional group. The reaction usually runs in a strong acidic, aqueous...
. When SO3 is added to water, rather than simply dissolving, it tends to form a fine mist of sulfuric acid, which is difficult to manage. However, SO3 added to concentrated sulfuric acid readily dissolves, forming oleum which can then be diluted with water to produce additional concentrated sulfuric acid.
As an intermediate for transportation
Oleum is a useful form for transporting sulfuric acid compounds, typically in rail tankcars, between oil refineries (which produce various sulfur compounds as a byproduct of refining) and industrial consumers.Certain compositions of oleum are solid at room temperature, and thus is safer to ship than when liquid. Solid oleum can then be converted into liquid at the destination through steam heating or dilution or concentration. This requires some care to prevent overheating and evaporation of sulfur trioxide. To extract it from a tank car requires careful heating using steam conduits within the tank car. Great care must be taken to avoid overheating, as this can increase the internal pressure within the tank car to a value exceeding the limit of the tank's safety valve
Safety valve
A safety valve is a valve mechanism for the automatic release of a substance from a boiler, pressure vessel, or other system when the pressure or temperature exceeds preset limits....
.
In Richmond, California
Richmond, California
Richmond is a city in western Contra Costa County, California, United States. The city was incorporated on August 7, 1905. It is located in the East Bay, part of the San Francisco Bay Area. It is a residential inner suburb of San Francisco, as well as the site of heavy industry, which has been...
in 1993 a significant release occurred due to overheating, causing a release of sulfur trioxide that absorbed moisture from the atmosphere, creating a mist of micrometre-sized sulfuric acid particles that formed an inhalation health hazard. This mist produced adverse health effects on residents and workers over a wide area.
Organic chemistry
Oleum is a harsh reagent, and is highly corrosive. One important use of oleum as a reagent is the secondary nitration of nitrobenzeneNitrobenzene
Nitrobenzene is an organic compound with the chemical formula C6H5NO2. It is a water-insoluble pale yellow oil with an almond-like odor. It freezes to give greenish-yellow crystals. It is produced on a large scale as a precursor to aniline. Although occasionally used as a flavoring or perfume...
. The first nitration
Nitration
Nitration is a general chemical process for the introduction of a nitro group into a chemical compound. The dominant application of nitration is for the production of nitrobenzene, the precursor to methylene diphenyl diisocyanate...
can occur with nitric acid in sulfuric acid, but this deactivates the ring towards further electrophilic substitution. A stronger reagent, oleum, is needed to introduce the second nitro group onto the aromatic ring.
Explosives manufacture
Oleum is used in the manufacture of many explosives with the notable exception of nitrocelluloseNitrocellulose
Nitrocellulose is a highly flammable compound formed by nitrating cellulose through exposure to nitric acid or another powerful nitrating agent. When used as a propellant or low-order explosive, it is also known as guncotton...
. The chemical requirements for explosives manufacture often call for anhydrous mixtures containing nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
and sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
. Ordinary commercial grade nitric acid consists of the constant boiling azeotrope
Azeotrope
An azeotrope is a mixture of two or more liquids in such a ratio that its composition cannot be changed by simple distillation. This occurs because, when an azeotrope is boiled, the resulting vapor has the same ratio of constituents as the original mixture....
of nitric acid and water, and contains 68% nitric acid. Mixtures of ordinary nitric acid in sulfuric acid therefore contain substantial amounts of water and are unsuitable for processes such as occur in the manufacture of trinitrotoluene.
Anhydrous nitric acid, referred to as white fuming nitric acid
White fuming nitric acid
White fuming nitric acid is a storable liquid oxidizer used with kerosene and hydrazine rocket fuel. It consists of nearly pure nitric acid . WFNA is commonly specified as containing no more than 2% water and less than 0.5% dissolved nitrogen dioxide or dinitrogen tetroxide.WFNA was sometimes...
, can be used to prepare water-free nitration
Nitration
Nitration is a general chemical process for the introduction of a nitro group into a chemical compound. The dominant application of nitration is for the production of nitrobenzene, the precursor to methylene diphenyl diisocyanate...
mixtures, and this method is used in laboratory scale operations where the cost of material is not of primary importance. Fuming nitric acid is very hazardous to handle and transport, because it is extremely corrosive and volatile. For industrial use, such strong nitration
Nitration
Nitration is a general chemical process for the introduction of a nitro group into a chemical compound. The dominant application of nitration is for the production of nitrobenzene, the precursor to methylene diphenyl diisocyanate...
mixtures are prepared by mixing oleum with ordinary commercial nitric acid so that the free sulfur trioxide in the oleum consumes the water in the nitric acid.
Reactions
Like concentrated sulfuric acid, oleum is such a strong dehydrating agent that if poured onto powdered glucoseGlucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
, or virtually any other sugar
Sugar
Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...
, it will draw the elements of water out of the sugar in an exothermic reaction, leaving nearly pure carbon as a solid. This carbon expands outward, hardening as a solid black substance with gas bubbles in it.