Sulfur trioxide

Last updated
Sulfur trioxide
SO3 meso.png
Sulfur-trioxide-3D-vdW.png
Names
Preferred IUPAC name
Sulfur trioxide
Systematic IUPAC name
Sulfonylideneoxidane
Other names
Sulfuric anhydride, Sulfur(VI) oxide
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.028.361 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 231-197-3
1448
PubChem CID
RTECS number
  • WT4830000
UNII
UN number UN 1829
  • InChI=1S/O3S/c1-4(2)3 Yes check.svgY
    Key: AKEJUJNQAAGONA-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/O3S/c1-4(2)3
    Key: AKEJUJNQAAGONA-UHFFFAOYAX
  • (monohydrate):InChI=1S/O3S.H2O/c1-4(2)3;/h;1H2
    Key: DEUOBQUHDSDIFY-UHFFFAOYSA-N
  • monomer:O=S(=O)=O
  • γ-trimer:O=S0(=O)OS(=O)(=O)OS(=O)(=O)O0
  • α/β polymer:OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)OS(=O)(=O)O
  • (monohydrate):O.O=S(=O)=O
Properties
SO3
Molar mass 80.066 g/mol
AppearanceColorless to white crystalline solid which will fume in air. [2] Colorless liquid and gas. [3]
Odor Varies. Vapor is pungent; like sulfur dioxide. [4] Mist is odorless. [3]
Density 1.92 g/cm3, liquid
Melting point 16.9 °C (62.4 °F; 290.0 K)
Boiling point 45 °C (113 °F; 318 K)
Reacts to give sulfuric acid
Thermochemistry
Std molar
entropy (S⦵298)
256.77 JK−1mol−1
−395.7 kJ/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
Highly corrosive, extremely strong dehydrating agent
GHS labelling:
GHS-pictogram-acid.svg GHS-pictogram-exclam.svg
Danger
H314, H335
P261, P280, P305+P351+P338, P310 [5]
NFPA 704 (fire diamond)
NFPA 704.svgHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g. hydrogen peroxideSpecial hazard W+OX: Reacts with water in an unusual or dangerous manner AND is oxidizer
3
0
3
W
OX
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
rat, 4 hr 375 mg/m3[ citation needed ]
Safety data sheet (SDS) ICSC 1202
Related compounds
Other cations
Selenium trioxide
Tellurium trioxide
Polonium trioxide
Related sulfur oxides
Sulfur monoxide
Sulfur dioxide
Related compounds
 Sulfuric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Sulfur trioxide (alternative spelling sulphur trioxide) is the chemical compound with the formula SO3. It has been described as "unquestionably the most [economically] important sulfur oxide". [1] It is prepared on an industrial scale as a precursor to sulfuric acid.

Contents

Sulfur trioxide exists in several forms: gaseous monomer, crystalline trimer, and solid polymer. Sulfur trioxide is a solid at just below room temperature with a relatively narrow liquid range. Gaseous SO3 is the primary precursor to acid rain. [6]

Molecular structure and bonding

Monomer

The molecule SO3 is trigonal planar. As predicted by VSEPR theory, its structure belongs to the D3h point group. The sulfur atom has an oxidation state of +6 and may be assigned a formal charge value as low as 0 (if all three sulfur-oxygen bonds are assumed to be double bonds) or as high as +2 (if the Octet Rule is assumed). [7] When the formal charge is non-zero, the S-O bonding is assumed to be delocalized. In any case the three S-O bond lengths are equal to one another, at 1.42 Å. [1] The electrical dipole moment of gaseous sulfur trioxide is zero.

Ball-and-stick model of the cyclic trimer of SO3 Sulfur-trioxide-trimer-from-xtal-1967-3D-balls-B.png
Ball-and-stick model of the cyclic trimer of SO3

Trimer

Both liquid and gaseous [8] SO3 exists in an equilibrium between the monomer and the cyclic trimer. The nature of solid SO3 is complex and at least 3 polymorphs are known, with conversion between them being dependent on traces of water. [9]

Absolutely pure SO3 freezes at 16.8 °C to give the γ-SO3 form, which adopts the cyclic trimer configuration [S(=O)2(μ-O)]3. [10] [1]

Polymer

An ampoule of sulfur trioxide Schwefeltrioxid Ampulle.jpg
An ampoule of sulfur trioxide


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. Structurally, it is the polymer [S(=O)2(μ-O)]n. Each end of the polymer is terminated with OH groups. [1] 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 water. [11]

Relative vapor pressures of solid SO3 are alpha < beta < gamma at identical temperatures, indicative of their relative molecular weights. Liquid sulfur trioxide has a 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". [11]

Chemical reactions

Sulfur trioxide undergoes many reactions. [1]

Hydration and hydrofluorination

SO3 is the anhydride of H2SO4. Thus, it is susceptible to hydration:

SO3 + H2O → H2SO4 (ΔfH = −200 kJ/mol) [12]

Gaseous sulfur trioxide fumes profusely even in a relatively dry atmosphere owing to formation of a sulfuric acid mist. SO3 is aggressively hygroscopic. The heat of hydration is sufficient that mixtures of SO3 and wood or cotton can ignite. In such cases, SO3 dehydrates these carbohydrates. [11]

Akin to the behavior of H2O, hydrogen fluoride adds to give fluorosulfuric acid:

SO3 + HF → FSO3H

Deoxygenation

SO3 reacts with dinitrogen pentoxide to give the nitronium salt of pyrosulfate:

2 SO3 + N2O5 → [NO2]2S2O7

Oxidant

Sulfur trioxide is an oxidant. It oxidizes sulfur dichloride to thionyl chloride.

SO3 + SCl2 → SOCl2 + SO2

Lewis acid

SO3 is a strong Lewis acid readily forming adducts with Lewis bases. [13] With pyridine, it gives the sulfur trioxide pyridine complex. Related adducts form from dioxane and trimethylamine.

Sulfonating agent

Sulfur trioxide is a potent sulfonating agent, i.e. it adds SO3 groups to substrates. Often the substrates are organic, as in aromatic sulfonation. [14] For activated substrates, Lewis base adducts of sulfur trioxide are effective sulfonating agents. [15]

Preparation

The direct oxidation of sulfur dioxide to sulfur trioxide in air proceeds very slowly:

2 SO2 + O2 → 2 SO3 (ΔH = −198.4 kJ/mol)

Industrial

Industrially SO3 is made by the contact process. Sulfur dioxide is produced by the burning of sulfur or iron pyrite (a sulfide ore of iron). After being purified by electrostatic precipitation, the SO2 is then oxidised by atmospheric oxygen at between 400 and 600 °C over a catalyst. A typical catalyst consists of vanadium pentoxide (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. [16] The majority of sulfur trioxide made in this way is converted into sulfuric acid.

Laboratory

Sulfur trioxide can be prepared in the laboratory by the two-stage pyrolysis of sodium bisulfate. Sodium pyrosulfate is an intermediate product: [17]

  1. Dehydration at 315 °C:
    2 NaHSO4 → Na2S2O7 + H2O
  2. Cracking at 460 °C:
    Na2S2O7 → Na2SO4 + SO3

The latter occurs at much lower temperatures (45–60 °C) in the presence of catalytic H2SO4. [18] In contrast, KHSO4 undergoes the same reactions at a higher temperature. [17]

Another two step method involving a salt pyrolysis starts with concentrated sulfuric acid and anhydrous tin tetrachloride:

  1. Reaction between tin tetrachloride and sulfuric acid in a 1:2 molar mixture at near reflux (114 °C):
    SnCl4 + 2 H2SO4 → Sn(SO4)2 + 4 HCl
  2. Pyrolysis of anhydrous tin(IV) sulfate at 150 °C - 200 °C:
    Sn(SO4)2 → SnO2 + 2 SO3

The advantage of this method over the sodium bisulfate one is that it requires much lower temperatures and can be done using normal borosilicate laboratory glassware without the risk of shattering. A disadvantage is that it generates significant quantities of hydrogen chloride gas which needs to be captured as well.

SO3 may also be prepared by dehydrating sulfuric acid with phosphorus pentoxide. [19]

Applications

Sulfur trioxide is a reagent in sulfonation reactions. Dimethyl sulfate is produced commercially by the reaction of dimethyl ether with sulfur trioxide: [20]

CH3OCH3 + SO3 → (CH3)2SO4

Sulfate esters are used as detergents, dyes, and pharmaceuticals. Sulfur trioxide is generated in situ from sulfuric acid or is used as a solution in the acid.

B2O3 stabilized sulfur trioxide was traded by Baker & Adamson under the tradename "Sulfan" in the 20th century. [21]

Safety

Along with being an oxidizing agent, sulfur trioxide is highly corrosive. It reacts violently with water to produce highly corrosive sulfuric acid.

See also

Related Research Articles

<span class="mw-page-title-main">Oxide</span> Chemical compound where oxygen atoms are combined with atoms of other elements

An oxide is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– ion with oxygen in the oxidation state of −2. Most of the Earth's crust consists of oxides. Even materials considered pure elements often develop an oxide coating. For example, aluminium foil develops a thin skin of Al2O3 that protects the foil from further oxidation.

<span class="mw-page-title-main">Sulfuric acid</span> Chemical compound (H₂SO₄)

Sulfuric acid or sulphuric acid, known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, and hydrogen, with the molecular formula H2SO4. It is a colorless, odorless, and viscous liquid that is soluble with water.

<span class="mw-page-title-main">Nitrous acid</span> Chemical compound

Nitrous acid is a weak and monoprotic acid known only in solution, in the gas phase, and in the form of nitrite salts. It was discovered by Carl Wilhelm Scheele, who called it "phlogisticated acid of niter". Nitrous acid is used to make diazonium salts from amines. The resulting diazonium salts are reagents in azo coupling reactions to give azo dyes.

An acidic oxide is an oxide that either produces an acidic solution upon addition to water, or acts as an acceptor of hydroxide ions effectively functioning as a Lewis acid. Acidic oxides will typically have a low pKa and may be inorganic or organic. A commonly encountered acidic oxide, carbon dioxide produces an acidic solution when dissolved.

The contact process is a method of producing sulfuric acid in the high concentrations needed for industrial processes. Platinum was originally used as the catalyst for this reaction; however, because it is susceptible to reacting with arsenic impurities in the sulfur feedstock, vanadium(V) oxide (V2O5) has since been preferred.

<span class="mw-page-title-main">Sulfonic acid</span> Organic compounds with the structure R−S(=O)2−OH

In organic chemistry, sulfonic acid refers to a member of the class of organosulfur compounds with the general formula R−S(=O)2−OH, where R is an organic alkyl or aryl group and the S(=O)2(OH) group a sulfonyl hydroxide. As a substituent, it is known as a sulfo group. A sulfonic acid can be thought of as sulfuric acid with one hydroxyl group replaced by an organic substituent. The parent compound is the parent sulfonic acid, HS(=O)2(OH), a tautomer of sulfurous acid, S(=O)(OH)2. Salts or esters of sulfonic acids are called sulfonates.

In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation state. The reverse of disproportionation, such as when a compound in an intermediate oxidation state is formed from precursors of lower and higher oxidation states, is called comproportionation, also known as symproportionation.

<span class="mw-page-title-main">Vanadium(V) oxide</span> Precursor to vanadium alloys and industrial catalyst

Vanadium(V) oxide (vanadia) is the inorganic compound with the formula V2O5. Commonly known as vanadium pentoxide, it is a dark yellow solid, although when freshly precipitated from aqueous solution, its colour is deep orange. Because of its high oxidation state, it is both an amphoteric oxide and an oxidizing agent. From the industrial perspective, it is the most important compound of vanadium, being the principal precursor to alloys of vanadium and is a widely used industrial catalyst.

<span class="mw-page-title-main">Sulfamic acid</span> Chemical compound

Sulfamic acid, also known as amidosulfonic acid, amidosulfuric acid, aminosulfonic acid, sulphamic acid and sulfamidic acid, is a molecular compound with the formula H3NSO3. This colourless, water-soluble compound finds many applications. Sulfamic acid melts at 205 °C before decomposing at higher temperatures to water, sulfur trioxide, sulfur dioxide and nitrogen.

<span class="mw-page-title-main">Disulfuric acid</span> Chemical compound

Disulfuric acid (alternative spelling disulphuric acid) or pyrosulfuric acid (alternative spelling pyrosulphuric acid), also named oleum, is a sulfur oxoacid. It is a major constituent of fuming sulfuric acid, oleum, and this is how most chemists encounter it. As confirmed by X-ray crystallography, the molecule consists of a pair of SO2(OH) groups joined by an oxide.

<span class="mw-page-title-main">Potassium bisulfate</span> Chemical compound

Potassium bisulfate (potassium bisulphate) is an inorganic compound with the chemical formula KHSO4 and is the potassium acid salt of sulfuric acid. It is a white, water-soluble solid.

<span class="mw-page-title-main">Chlorosulfuric acid</span> Chemical compound

Chlorosulfuric acid (IUPAC name: sulfurochloridic acid) is the inorganic compound with the formula HSO3Cl. It is also known as chlorosulfonic acid, being the sulfonic acid of chlorine. It is a distillable, colorless liquid which is hygroscopic and a powerful lachrymator. Commercial samples usually are pale brown or straw colored.

Selenium trioxide is the inorganic compound with the formula SeO3. It is white, hygroscopic solid. It is also an oxidizing agent and a Lewis acid. It is of academic interest as a precursor to Se(VI) compounds.

Sulfation is the chemical reaction that entails the addition of SO3 group. In principle, many sulfations would involve reactions of sulfur trioxide (SO3). In practice, most sulfations are effected less directly. Regardless of the mechanism, the installation of a sulfate-like group on a substrate leads to substantial changes.

<span class="mw-page-title-main">Potassium pyrosulfate</span> Chemical compound

Potassium pyrosulfate, or potassium disulfate, is an inorganic compound with the chemical formula K2S2O7.

<span class="mw-page-title-main">Calcium sulfite</span> Chemical compound

Calcium sulfite, or calcium sulphite, is a chemical compound, the calcium salt of sulfite with the formula CaSO3·x(H2O). Two crystalline forms are known, the hemihydrate and the tetrahydrate, respectively CaSO3·½(H2O) and CaSO3·4(H2O). All forms are white solids. It is most notable as the product of flue-gas desulfurization.

<span class="mw-page-title-main">Hydroxylammonium sulfate</span> Chemical compound

Hydroxylammonium sulfate [NH3OH]2SO4, is the sulfuric acid salt of hydroxylamine. It is primarily used as an easily handled form of hydroxylamine, which is explosive when pure.

Sodium pyrosulfate is an inorganic compound with the chemical formula of Na2S2O7. It is a colorless salt. It hydrolyses in water to form sodium bisulfate with a chemical formula of NaHSO4 which has a pH of around 1.

The chalcogens react with each other to form interchalcogen compounds.

Gold(III) sulfide or auric sulfide is an inorganic compound with the formula Au2S3. Auric sulfide has been described as a black and amorphous solid. Only the amorphous phase has been produced, and the only evidence of existence is based on thermal analysis.

References

  1. 1 2 3 4 5 6 Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. pp. 703–704. ISBN   978-0-08-037941-8.
  2. ↑ "SULFUR TRIOXIDE CAMEO Chemicals NOAA". Cameochemicals.noaa.gov.
  3. 1 2 Lerner, L. (2011). Small-Scale Synthesis of Laboratory Reagents with Reaction Modeling. CRC Press. p. 10. ISBN   9781439813133. LCCN   2010038460.
  4. ↑ "Substance:Sulfur trioxide - Learn Chemistry Wiki". Rsc.org.
  5. ↑ "Sulfur trioxide 227692" (PDF). SO3. Archived from the original on 2020-09-01. Retrieved 1 September 2020.
  6. ↑ Thomas Loerting; Klaus R. Liedl (2000). "Toward elimination of descrepancies between theory and experiment: The rate constant of the atmospheric conversion of SO3 to H2SO4". Proceedings of the National Academy of Sciences of the United States of America. 97 (16): 8874–8878. Bibcode:2000PNAS...97.8874L. doi: 10.1073/pnas.97.16.8874 . PMC   16788 . PMID   10922048.
  7. ↑ Housecroft, Catherine E.; Sharpe, Alan G. (2012). Inorganic Chemistry (4 ed.). Essex, England: Pearson. p. 575.
  8. ↑ Lovejoy, R. W.; Colwell, J. H.; Eggers, D. F.; Halsey, G. D. (February 1962). "Infrared Spectrum and Thermodynamic Properties of Gaseous Sulfur Trioxide". The Journal of Chemical Physics. 36 (3): 612–617. Bibcode:1962JChPh..36..612L. doi:10.1063/1.1732581.
  9. ↑ Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, ISBN   0-12-352651-5
  10. ↑ Westrik, R.; Mac Gillavry, C. H. (1941). "The crystal structure of the ice-like form of sulphur trioxide (γ-modification)". Recueil des Travaux Chimiques des Pays-Bas. 60 (11): 794–810. doi:10.1002/recl.19410601102.
  11. 1 2 3 Merck Index of Chemicals and Drugs, 9th ed. monograph 8775
  12. ↑ "The Manufacture of Sulfuric Acid and Superphosphate" (PDF). Chemical Processes in New Zealand. Archived from the original (PDF) on 2018-01-27. Retrieved 2016-04-22.
  13. ↑ Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience, ISBN   0-471-19957-5
  14. ↑ Weil, J. K.; Bistline Jr., R. G.; Stirton, A. J. (1956). "α-Sulfopalmitic Acid". Organic Syntheses. 36: 83. doi:10.15227/orgsyn.036.0083.
  15. ↑ Rondestvedt Jr., Christian S.; Bordwell, F. G. (1954). "Sodium β-Styrenesulfonate and β-Styrenesulfonyl Chloride". Organic Syntheses. 34: 85. doi:10.15227/orgsyn.034.0085.
  16. ↑ Hermann Müller "Sulfuric Acid and Sulfur Trioxide" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. 2000 doi : 10.1002/14356007.a25_635
  17. 1 2 K.J. de Vries; P.J. Gellings (May 1969). "The thermal decomposition of potassium and sodium-pyrosulfate". Journal of Inorganic and Nuclear Chemistry. 31 (5): 1307–1313. doi:10.1016/0022-1902(69)80241-1.
  18. ↑ GarageChemist. "Preparation of Sulfur Trioxide and Oleum" (PDF). pp. 1–2.
  19. ↑ "How to make sulfur trioxide - YouTube". www.youtube.com. 21 September 2017. Retrieved 1 September 2020.
  20. ↑ Weisenberger, Karl; Mayer, Dieter; Sandler, Stanley R. (2000). "Dialkyl Sulfates and Alkylsulfuric Acids". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a08_493. ISBN   978-3-527-30385-4.
  21. ↑ Habashi, Fathi; Dugdale, Raymond (June 1973) [1972-11-06]. "The Action of Sulfur Trioxide on Chalcopyrite". Metallurgical and Materials Transactions . B-4 (6): 1553–1556. Bibcode:1973MT......4.1553H. doi:10.1007/BF02668007. S2CID   93744787. p. 1553: Sulfur trioxide used was pure, colorless liquid SO3 marketed under the trade name Sulfan by Baker and Adamson

Sources

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