Oleum
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Oleum is another name for Fuming Sulphuric Acid which, because of its composition, is often referred to as Disulphuric Acid (Pyrosulphuric Acid). It consists of varying amounts of Sulphur Trioxide in Sulphuric Acid taking the general formula ySO3.H2O where y refers to the total molar Sulphur Trioxide content. Another way of expressing the general formula is H2SO4.𝔁SO3 where 𝔁 represents the molar free Sulphur Trioxide content which is used to assay Oleum. Varying the value of 𝔁 will produce different Oleums, when 𝔁 = 1, then Disulphuric Acid (H2S2O7) is produced. In its pure form this substance is solid at room temperature with a melting point of 36 degrees C.
Oleum is produced in the 'contact process' when Sulphur Trioxide, formed by oxidation of Sulphur, is dissolved in Sulphuric Acid.
The properties of Oleums can be used to provide a safer means of transporting Sulphuric Acid compounds. Being solid at room temperature, Oleums can be shipped by tanker and converted to liquid form at their destination by steam heating, dilution or concentration.
Oleum can be used in the following reactions:-
- Benzene is sulphonated by Oleum to Benzenesulphonic Acid
C6H6 + H2S2O7 -> C6H6SO3H + H2SO4 - Toluene is sulphonated to p-Toluenesulphonic Acid
C6H5CH3 + H2S2O7 + H2O -> C6H4CH3SO3H. H2O + H2SO4 - Sulphuric Acid is formed by adding Oleum to water
H2S2O7 + H2O -> 2H2SO4
The Molecular Mass of Oleum is 178.14
The Density of Oleum is 1.94g/cm3
Purity is approximately 30% which is based on the free SO3 content.
Hazards of Oleum
- Extremely Corrosive, causing severe eye and skin burns
- Harmful if inhaled causing damage to nose, throat and lungs
- Violent reaction with water, producing heat (exothermic)
- Reacts with most metals to produce explosive hydrogen gas
- Ingestion results in burns to mouth, throat and oesophagus
- Reactions with organic materials such as chlorates, carbides, fulminates and picrates may cause fire and explosions
- Do not allow to enter watercourses or sewers
- Oleum is harmful to aquatic life and will cause a pH shift to water
- Hazardous degradation products are Sulphur Oxides SO2, SO3
- For transportation Oleum is given the shipping name Sulphuric Acid, Fuming and UN Number 1831
- Oleum belongs to Packing Group I, the highest group, denoting its Corrosive properties.
- Oleum is Primary Class 8 ‘Corrosive’ with Subsidiary Hazard Class 6.1 ‘Toxic’. There is no Limited Quantity which means all amounts of Oleum transported are covered by the transport regulations.
http://www.sulphuric-acid.co.uk/oleum | Saved Friday, November 18th, 2011 - 6:11 AM