p-Toluenesulfonic acid

p-Toluenesulfonic acid
p-Toluenesulfonic acid[1]
CAS number 104-15-4 YesY
6192-52-5 (monohydrate)
PubChem 6101
ChemSpider 5876 YesY
DrugBank DB03120
KEGG C06677 YesY
Jmol-3D images Image 1
Molecular formula CH3C6H4SO3H
Molar mass 172.20 g/mol (anhydrous)
190.22 g/mol (monohydrate)
Appearance colorless (white) solid
Density 1.24 g/cm3
Melting point

38 °C, 311 K (anhydrous) [2]
103-106 °C, 376-379 K (monohydrate)

Boiling point

140 °C, 413 K, 284 °F (at 20 mmHg)

Solubility in water 67 g/100 mL
Acidity (pKa) -2.8 (water),[3]

8.5 (acetonitrile)[4]

Molecular shape tetrahedral at S
MSDS External MSDS
R-phrases R36/37/38
S-phrases S26
Main hazards skin irritant
Related compounds
Related sulfonic acids Benzenesulfonic acid
Sulfanilic acid
 N (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

p-Toluenesulfonic acid (PTSA) or tosylic acid (TsOH) is an organic compound with the formula CH3C6H4SO3H. It is a white solid that is soluble in water, alcohols, and other polar organic solvents. The 4-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.

TsOH is a strong organic acid, about a million times stronger than benzoic acid. It is one of the few strong acids that are solid and, hence, conveniently weighed. Also, unlike some of the strong mineral acids (especially nitric acid, sulfuric acid, and perchloric acid), TsOH is non-oxidizing.




Preparation and handling

TsOH is prepared on an industrial scale by the sulfonation of toluene. It hydrates readily. Common impurities include benzenesulfonic acid and sulfuric acid. Impurities can be removed by recrystallization from its concentrated aqueous solution followed by azeotropic drying with toluene.[5]

Toluenesulfonic acid finds use in organic synthesis as an "organic-soluble" acid catalyst. Examples of uses:

Tosylate esters

Ball-and-stick model of the tosylate anion

A tosylate ester has a limited shelf life in air due to its ready hydrolysis in the presence of light. The tosyl group is electron-withdrawing, which makes tosylates excellent leaving groups. The tosyl group is also a protecting group for alcohols and amines, prepared by combining the alcohol with 4-toluenesulfonyl chloride, usually in an aprotic solvent, often pyridine, the basicity of which activates the reaction.[9] Toluenesulfonate esters undergo nucleophilic attack or elimination.


  • p-Toluenesulfonic acid may be converted to phosphorus pentoxide.[10]
  • When toluene sulphonic acid (o-, m-, p-,) is boiled with HCl or treated with super-heated steam, toluene is formed along with H2SO4

CH3C6H4SO3H (Toluene Sulphonic acid) + HOH (steam) → C6H5CH3 (Toluene) + H2SO4 (Sulfuric acid)

See also


  1. ^ Merck Index, 11th Edition, 9459.
  2. ^ Armarego, Wilfred (2003). Purification of Laboratory Chemicals. Elsevier Science. pp. 370. ISBN 0-7506-7571-3. 
  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. ^ Perrin, D. D. and Armarego, W. L. F., Purification of Laboratory Chemicals, Pergamon Press: Oxford, 1988.
  6. ^ H. Griesser, H.; Öhrlein, R.; Schwab, W.; Ehrler, R.; Jäger, V. (2004), "3-Nitropropanal, 3-Nitropropanol, and 3-Nitropropanal Dimethyl Acetal", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=v77p0236 ; Coll. Vol. 10: 577 
  7. ^ 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", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv9p0722 ; Coll. Vol. 9: 722 
  8. ^ Imwinkelried, R.; Schiess, M.; Seebach, D. (1993), "Diisopropyl (2S,3S)-2,3-O-isopropylidenetartrate", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv8p0201 ; Coll. Vol. 8: 201 
  9. ^ Nucleophilic Substitution
  10. ^ L. Field and J. W. McFarland (1963), "p-Toluenesulfonic Anhydride", Org. Synth., http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv4p0940 ; Coll. Vol. 4: 940 

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