P-Toluenesulfonic acid


p-Toluenesulfonic acid (PTSA or pTsOH) or tosylic acid (TsOH) is an organic compound with the formula CH3C6H4SO3H. It is a white extremely hygroscopic solid that is soluble in water, alcohols, and other polar organic solvents.[6] The CH3C6H4SO2 group is known as the tosyl group and is often abbreviated as Ts or Tos. Most often, TsOH refers to the monohydrate, TsOH.H2O.[6]

p-Toluenesulfonic acid[1]
Tosic acid.png
P-toluenesulfonic acid.png
Slightly impure sample of the monohydrate
Preferred IUPAC name
4-Methylbenzene-1-sulfonic acid
Other names
4-Methylbenzenesulfonic acid
Tosylic acid
tosic acid
  • 104-15-4 checkY
  • 6192-52-5 (monohydrate) checkY
3D model (JSmol)
  • Interactive image
  • CHEBI:27849 checkY
  • ChEMBL541253 checkY
  • 5876 checkY
  • DB03120 checkY
ECHA InfoCard 100.002.891 Edit this at Wikidata
  • C06677 checkY
  • 6101
  • QGV5ZG5741 checkY
  • 3BTO78GAFF ((monohydrate) checkY
  • DTXSID0026701 Edit this at Wikidata
  • InChI=1S/C7H8O3S/c1-6-2-4-7(5-3-6)11(8,9)10/h2-5H,1H3,(H,8,9,10) checkY
  • InChI=1/C7H8O3S/c1-6-2-4-7(5-3-6)11(8,9)10/h2-5H,1H3,(H,8,9,10)
  • Cc1ccc(cc1)S(=O)(=O)O
Molar mass 172.20 g/mol (anhydrous)
190.22 g/mol (monohydrate)
Appearance colorless (white) solid
Density 1.24 g/cm3
Melting point 105 to 107 °C (221 to 225 °F; 378 to 380 K) (monohydrate)[2]
38 °C (100 °F; 311 K) (anhydrous)[2]
Boiling point 140 °C (284 °F; 413 K) at 20 mmHg
67 g/100 mL
Acidity (pKa) −2.8 (water) reference for benzenesulfonic acid,[3]

8.5 (acetonitrile)[4]

tetrahedral at S
Occupational safety and health (OHS/OSH):
Main hazards
skin irritant
GHS labelling:[5]
GHS07: Exclamation mark
H315, H319, H335
P302+P352, P305+P351+P338
Safety data sheet (SDS) External MSDS
Related compounds
Related sulfonic acids
Benzenesulfonic acid
Sulfanilic acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

As with other aryl sulfonic acids, TsOH is a strong organic acid. It is about one million times stronger than benzoic acid.[6] It is one of the few strong acids that is solid and therefore is conveniently weighed and stored.

Preparation and usesEdit

TsOH is prepared on an industrial scale by the sulfonation of toluene. Common impurities include benzenesulfonic acid and sulfuric acid. TsOH monohydrate contains an amount of water. To estimate the total moisture present as impurity, the Karl Fischer method is used.[citation needed] Impurities can be removed by recrystallization from its concentrated aqueous solution followed by azeotropic drying with toluene.[2]

TsOH finds use in organic synthesis as an "organic-soluble" strong acid. Examples of uses include:


Alkyl tosylates are alkylating agents because tosylate is electron-withdrawing as well as a good leaving group. Tosylate is a pseudohalide. Toluenesulfonate esters undergo nucleophilic attack or elimination. Reduction of tosylate esters gives the hydrocarbon. Thus, tosylation followed by reduction allows for the deoxygenation of alcohols.

Structures of the 7-norbornenyl cation with p-orbital stabilization.

In a famous and illustrative use of tosylate, 2-norbornyl cation was displaced from the 7-norbornenyl tosylate. The elimination occurs 1011 times faster than the solvolysis of anti-7-norbornyl p-toluenesulfonate.[10]

Tosylates are also protecting group for alcohols. They are prepared by combining the alcohol with 4-toluenesulfonyl chloride, usually in an aprotic solvent, often pyridine.[11]


CH3C6H4SO3H + H2O → C6H5CH3 + H2SO4

This reaction is general for aryl sulfonic acids.[13][14]

See alsoEdit


  1. ^ Merck Index, 11th Edition, 9459.
  2. ^ a b c Armarego, W. L. F. (2003). Purification of Laboratory Chemicals (8th ed.). Oxford: Elsevier Science. p. 612. ISBN 978-0-12-805457-4.
  3. ^ Guthrie, J. P. Hydrolysis of esters of oxy acids: pKa values for strong acids. Can. J. Chem. 1978, 56, 2342-2354.
  4. ^ Eckert, F.; Leito, I.; Kaljurand, I.; Kütt, A.; Klamt, A.; Diedenhofen, M. Prediction of Acidity in Acetonitrile Solution with COSMO-RS. J. Comput. Chem. 2009, 30, 799-810. doi:10.1002/jcc.21103
  5. ^ GHS: GESTIS 510754
  6. ^ a b c Baghernejad, Bita (31 August 2011). "Application of p-toluenesulfonic Acid (PTSA) in Organic Synthesis". Current Organic Chemistry. 15 (17). doi:10.2174/138527211798357074.
  7. ^ H. Griesser, H.; Öhrlein, R.; Schwab, W.; Ehrler, R.; Jäger, V. (2004). "3-Nitropropanal, 3-Nitropropanol, and 3-Nitropropanal Dimethyl Acetal". Organic Syntheses.; Collective Volume, vol. 10, p. 577
  8. ^ Furuta, K.; Gao, Q.-z.; Yamamoto, H. (1998). "Chiral (Acyloxy)borane Complex-catalyzed Asymmetric Diels-Alder Reaction: (1R)-1,3,4-Trimethyl-3-cyclohexene-1-carboxaldehyde". Organic Syntheses.; Collective Volume, vol. 9, p. 722
  9. ^ Imwinkelried, R.; Schiess, M.; Seebach, D. (1993). "Diisopropyl (2S,3S)-2,3-O-isopropylidenetartrate". Organic Syntheses.; Collective Volume, vol. 8, p. 201
  10. ^ Winstein, S.; Shatavsky, M.; Norton, C.; Woodward, R. B. (1955-08-01). "7-Norbornenyl and 7-Norbornyl cations". Journal of the American Chemical Society. 77 (15): 4183–4184. doi:10.1021/ja01620a078. ISSN 0002-7863.
  11. ^ "Nucleophilic Substitution".
  12. ^ L. Field & J. W. McFarland (1963). "p-Toluenesulfonic Anhydride". Organic Syntheses.; Collective Volume, vol. 4, p. 940
  13. ^ C. M. Suter (1944). The Organic Chemistry of Sulfur. New York: John Wiley & Sons. pp. 387–388.
  14. ^ J. M. Crafts (1901). "Catalysis in concentrated solutions". J. Am. Chem. Soc. 23 (4): 236–249. doi:10.1021/ja02030a007.