Sulfur trioxide

• Sulfuric
• Sulfur ( VI) oxide
• Acidum sulph anhydricum

Colorless fumes in the air mass

Fixed ( α -, β - form), liquid ( γ - form)

2.00 g · cm -3 ( γ - form)

62.2 ° C ( α ), 32.5 ° C ( β - ) 16.8 ° C ( γ - form)

44.45 ° C ( β -, γ - form), α - form is decomposed at 50 ° C.

260 hPa ( 20 ° C)

Explosive hydrolysis in water

Risk

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Sulfur trioxide, SO3 is the anhydride of sulfuric acid. It forms under standard conditions colorless needle -shaped crystals that are extremely hygroscopic and very violent ( explosive) react with water. There are three different modifications for the solid sulfur trioxide. Inhalation Irritation symptoms has resulted in the lungs resulting sulfuric acid which can cause a life-threatening pulmonary edema.

Extraction

Sulfur trioxide is prepared industrially by the contact method with vanadium pentoxide catalyzed oxidation of sulfur dioxide with oxygen in the air at 420 ° C. Pure sulfur trioxide is obtained by distillation of oleum, which is an intermediate in the production of sulfuric acid. The first gaseous sulfur trioxide distilled is then condensed by cooling to liquid sulfur trioxide. Condensation and Storage narrow temperature limits are complied with, since the fixed point and boiling point are very close together.

To obtain smaller amounts of sulfur trioxide, can also be distilled off from a mixture of sulfuric acid and phosphorus pentoxide or metaphosphoric ( H4P4O12, cyclic phosphate). Sulfur trioxide can be represented but also by the oxidation of sulfur dioxide with nitrogen dioxide.

Use

Gaseous sulfur trioxide is mainly used for the production of sulfuric acid:

In water, the gaseous SO3 dissolves only very slowly and is therefore introduced into concentrated sulfuric acid, with disulphuric forms ( H2S2O7 ). With this water is then converted to sulfuric acid:

Skip to producing fluorosulphonic and chlorosulfonic

If we mix sulfur with alcohols, esters of sulfuric acid occur:

This reaction is used in the production of surfactants:

The sulfuric acid esters are neutralized with sodium hydroxide solution and thus provide fatty alcohol sulfates. Further sulfur trioxide is suitable as the oxidizing agent. It was also used for the production of smoke grenades, as a drop of liquid sulfur trioxide may already einnebeln complete a large space.

Properties

Gaseous sulfur trioxide is present as a monomer. This is built trigonal planar and contains three equal S- O double bonds:

The specified structural formula is made up as follows -looking resonance structures together:

There is in equilibrium with S3O9 molecules. If ( gaseous ) SO3 cooled below -80 ° C, the so-called γ - SO3 forms. This consists of S3O9 molecules. It is not a planar structure, but forms a corrugated ring. The sulfur atoms of oxygen are distorted tetrahedrally surrounded.

Sulfur trioxide instantly charred rubber and most plastics such as PVC, only special plastics such as Teflon and Perfluoralkoxy are relatively resistant.