''p''-Toluenesulfonic acid

p-Toluenesulfonic acid[1]
Names
Preferred IUPAC name
4-Methylbenzene-1-sulfonic acid
Other names
4-Methylbenzenesulfonic acid
Tosylic acid
tosic acid
PTSA
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
DrugBank
ECHA InfoCard 100.002.891
KEGG
UNII
Properties
C7H8O3S
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 (100 °F; 311 K) (anhydrous)[2]
103 to 106 °C (217 to 223 °F; 376 to 379 K) (monohydrate)
Boiling point 140 °C (284 °F; 413 K) at 20 mmHg
67 g/100 mL
Acidity (pKa) −2.8 (water),[3]

8.5 (acetonitrile)[4]

Structure
tetrahedral at S
Hazards
Main hazards skin irritant
Safety data sheet External MSDS
R-phrases (outdated) R36/37/38
S-phrases (outdated) S26
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

p-Toluenesulfonic acid (PTSA or pTsOH) 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 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.

As with other sulfonic acids, TsOH is a strong organic acid. It is about one 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.

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]

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

Tosylate esters

Ball-and-stick model of the tosylate anion

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

CH3C6H4SO3H + H2O → C6H5CH3 + H2SO4

This reaction is general for aryl sulfonic acids, but the rate at which it occurs depends upon the structure of the acid, the temperature and the nature of the catalyzing acid. For example, TsOH is unaffected by cold concentrated hydrochloric acid, but hydrolyzes when heated to 186 °C in concentrated phosphoric acid.[11][12]

See also

References

  1. ↑ Merck Index, 11th Edition, 9459.
  2. ↑ Armarego, Wilfred (2003). Purification of Laboratory Chemicals. Elsevier Science. p. 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. & Armarego, W. L. F. (1988). Purification of Laboratory Chemicals. Oxford: Pergamon Press.
  6. ↑ H. Griesser, H.; Öhrlein, R.; Schwab, W.; Ehrler, R.; Jäger, V. (2004). "3-Nitropropanal, 3-Nitropropanol, and 3-Nitropropanal Dimethyl Acetal". Org. Synth.; Coll. Vol., 10, p. 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.; Coll. Vol., 9, p. 722
  8. ↑ Imwinkelried, R.; Schiess, M.; Seebach, D. (1993). "Diisopropyl (2S,3S)-2,3-O-isopropylidenetartrate". Org. Synth.; Coll. Vol., 8, p. 201
  9. ↑ "Nucleophilic Substitution".
  10. ↑ L. Field and J. W. McFarland (1963). "p-Toluenesulfonic Anhydride". Org. Synth.; Coll. Vol., 4, p. 940
  11. ↑ C. M. Suter (1944). The Organic Chemistry of Sulfur. New York: John Wiley & Sons. pp. 387–388.
  12. ↑ J. M. Crafts (1901). "Catalysis in concentrated solutions". J. Am. Chem. Soc. 23: 236–249.
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