- Sulfur trioxide
Name = Sulfur trioxide
ImageFileL1 = Sulfur-trioxide-2D.svg
ImageSizeL1 = 120px
ImageFileR1 = Sulfur-trioxide-3D-vdW.png
ImageSizeR1 = 120px
ImageName = Sulfur trioxide
OtherNames = Sulfuric anhydride
Section1 = Chembox Identifiers
CASNo = [7446-11-9]
Section2 = Chembox Properties
Formula = SO3
MolarMass = 80.06 g mol−1
Density = 1.92 g cm−3
Solvent = other solvents
SolubleOther = Hydrolysis with
MeltingPt = 16.9 °C, 62.4 °F
BoilingPt = 45 °C, 113 °F
Section4 = Chembox Thermochemistry
DeltaHf = −397.77 kJ/mol
Entropy = 256.77 J.K−1.mol−1
Section7 = Chembox Hazards
RPhrases = R14, R35, R37
SPhrases = S1/2, S26, S30, S45
Section8 = Chembox Related
OtherCpds = SO2
Sulfurtrioxide (also spelled sulphur 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 scale as a precursor to sulfuric acid.
tructure and bonding
Gaseous SO3 is a
trigonal planarmolecule of D3h symmetry, as predicted by VSEPR theory.
In terms of electron-counting formalisms, the sulfur atom has an oxidation state of +6, a formal charge of 0, and is surrounded by 6 electron pairs. From the perspective of
molecular orbital theory, most of these electron pairs are non-bonding in character, as is typical for hypervalent molecules.
Sulfur trioxide also exhibits hybridization.
SO3 is the
anhydrideof H2SO4. Thus, the following reaction occurs::SO3(l) + H2O(l) → H2SO4(l) (-88 kJ mol−1)The reaction occurs both rapidly and exothermically. At or above ~340 °C, sulfuric acid, sulfur trioxide, and water coexist in significant equilibrium concentrations.
Sulfur trioxide also reacts with
sulfur dichlorideto yield the useful reagent, thionyl chloride.
:SO3 + SCl2 → SOCl2 + SO2
Sulfur Trioxide reacts with
waterto create sulfuric acid, though the reaction is too violent to be used in large-scale manufacturing.
SO3 is a strong Lewis acid readily forming crystalline complexes with pyridine ,
dioxaneand trimethylaminewhich can be used as sulfonating agents [Cotton&Wilkinson6th] .
Sulfur trioxide can be prepared in the laboratory by the two-stage
pyrolysisof sodium bisulfate. Sodium pyrosulfateis an intermediate product:;1) dehydration:: 2NaHSO4 → Na2S2O7 + H2O @ 315°C;2) cracking:: Na2S2O7 → Na2SO4 + SO3 @ 460°CThis method will work for other metal bisulfates, the controlling factor being the stability of the intermediate pyrosulfate salt.
Industrially SO3 is made by the
contact process. Sulfur dioxide, generally made by the burning of sulfuror iron pyrite(a sulfide ore of iron), is first purified by electrostatic precipitation. The purified SO2 is then oxidised by atmospheric oxygenat between 400 and 600 °C over a catalyst consisting of vanadiumpentoxide V2O5 activated with potassium oxide K2O on kieselguhr or silica support. Platinum also works very well but is too expensive and is poisoned (rendered ineffective) much more easily by impurities.
The majority of sulphur trioxide made in this way is converted into
sulfuric acidnot by the direct addition of water, with which it forms a fine mist, but by absorption in concentrated sulfuric acid and dilution with water of the produced oleum.
tructure of solid SO3
The nature of solid SO3 is a surprisingly complex area because of structural changes caused by traces of water. [Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.] Upon condensation of the gas, absolutely pure SO3 condenses into a trimer, which is often called "γ"-SO3. This molecular form is a colorless solid with a melting point of 16.8 °C. It adopts a cyclic structure described as [S(=O)2("μ"-O)] 3Advanced Inorganic Chemistry by Cotton and Wilkinson, 2nd ed p543] .
If SO3 is condensed above 27 °C, then "α"-"SO3" forms, which has a melting point of 62.3°C. "α"-SO3 is fibrous in appearance, like asbestos (with which it has no chemical relationship). Structurally, it is the
polymer[S(=O)2("μ"-O)] "n". Each end of the polymer is terminated with OH groups (hence "α"-"SO3" is not really a form of SO3). "β"-SO3, like the alpha form, is fibrous but of different molecular weight, consisting of an hydroxyl-capped polymer, but melts at 32.5 °C. Both the gamma and the beta forms are metastable, eventually converting to the stable alpha form if left standing for sufficient time. This conversion is caused by traces of waterMerck Index of Chemicals and Drugs, 9th ed. monograph 8775] .
Relative vapor pressures of solid SO3 are alpha< beta< gamma at identical temperatures, indicative of their relative
molecular weights. Liquid sulfur trioxide has vapor pressure consistent with the gamma form. Thus heating a crystal of "α"-SO3 to its melting point results in a sudden increase in vapor pressure, which can be forceful enough to shatter a glass vessel in which it is heated. This effect is known as the "alpha explosion."
* [http://www.webelements.com/ WebElements]
* [http://webbook.nist.gov/chemistry/ NIST Standard Reference Database]
* [http://ecb.jrc.it/ European Chemicals Bureau]
Sulfur trioxide pyridine complex
Wikimedia Foundation. 2010.
Look at other dictionaries:
sulfur trioxide — noun : a compound SO3 that is a heavy low boiling strongly acid corrosive liquid when first produced at ordinary temperatures but that polymerizes readily to three or more solid forms including a stable modification resembling asbestos, that is… … Useful english dictionary
sulfur trioxide — sieros(VI) oksidas statusas T sritis chemija formulė SO₃ atitikmenys: angl. sulfur trioxide; sulfur(VI) oxide rus. серный ангидрид; серы триоксид; серы(VI) оксид ryšiai: sinonimas – sieros trioksidas … Chemijos terminų aiškinamasis žodynas
sulfur trioxide — Chem. an irritant, corrosive, low melting solid, SO3, obtained by the oxidation of sulfur dioxide, used as an intermediate in the manufacture of sulfuric acid. Also called sulfuric anhydride. [1865 70] * * * … Universalium
sulfur trioxide — noun A corrosive liquid, SO, which forms sulfuric acid on contact with water; made commercially by the oxidation of sulfur dioxide … Wiktionary
Sulfur trioxide pyridine complex — Chembox new ImageFileL1 = Sulfur trioxide pyridine complex 2D skeletal.png ImageSizeL1 = ImageFileR1 = Sulfur trioxide pyridine complex 3D vdW.png ImageSizeR1 = IUPACName = OtherNames = Section1 = Chembox Identifiers PubChem = CASNo = 26412 87 3… … Wikipedia
Sulfur oxide — (SOx) refers to one or more of the following:* Lower sulfur oxides (SnO, S7O2 and S6O2) * Sulfur monoxide (SO) * Sulfur dioxide (SO2) * Sulfur trioxide (SO3) *Higher sulfur oxides (SO3+x where 0 … Wikipedia
sulfur oxide — ▪ chemical compound any of several compounds of sulfur and oxygen, the most important of which are sulfur dioxide (SO2) and sulfur trioxide (SO3), both of which are manufactured in huge quantities in intermediate steps of sulfuric acid… … Universalium
sulfur — /sul feuhr/, n. 1. Also, esp. Brit., sulphur. Chem. a nonmetallic element that exists in several forms, the ordinary one being a yellow rhombic crystalline solid, and that burns with a blue flame and a suffocating odor: used esp. in making… … Universalium
Sulfur — This article is about the chemical element. For other uses, see Sulfur (disambiguation). phosphorus ← sulfur → chlorine … Wikipedia
Sulfur dioxide — Chembox new Name = Sulphur dioxide ImageFileL1 = Sulfur dioxide 2D.svg ImageSizeL1 = 120 ImageFileR1 = Sulfur dioxide 3D vdW.png OtherNames = sulfur(IV) oxide; sulfurous anhydride Section1 = Chembox Identifiers CASNo = CASRN|7|4|4|6|0|9|5… … Wikipedia