p-Toluenesulfonic acid

p-Toluenesulfonic acid[1]
IUPAC name

4-methylbenzenesulfonic acid
Other names

Tosylic acid
tosic acid
PTSA
Identifiers
CAS number 104-15-4 Y, 
6192-52-5 (monohydrate)
PubChem 6101
ChemSpider 5876 Y
DrugBank DB03120
KEGG C06677 Y
ChEBI CHEBI:27849 N
ChEMBL CHEMBL541253 Y
Jmol-3D images Image 1
Properties
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]
Structure
Molecular shape tetrahedral at S
Hazards
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: Y/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 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 is solid and, hence, conveniently weighed. Also, unlike some strong mineral acids (especially nitric acid, sulfuric acid, and perchloric acid), TsOH is non-oxidizing.

Contents

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

Tosylate esters are used as alkylating agents because the tosyl group is electron-withdrawing, which makes the tosylate anion a good leaving group. 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. Reduction of tosylate esters gives the hydrocarbon. Thus, tosylation followed by reduction allows for the deoxygenation of alcohols.

Reactions

p-Toluenesulfonic acid may be converted to p-toluenesulfonic anhydride by heating with phosphorus pentoxide.[10] When TsOH (any isomers) is treated with acid and water, toluene is formed:

CH3C6H4SO3H + H2O → C6H5CH3 + H2SO4

See also

References

  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