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
SMILES Cc1ccc(cc1)S(=O)(=O)O
InChI InChI=1S/C7H8O3S/c1-6-2-4-7(5-3-6)11(8,9)10/h2-5H,1H3,(H,8,9,10) Y Key: JOXIMZWYDAKGHI-UHFFFAOYSA-N Y InChI=1/C7H8O3S/c1-6-2-4-7(5-3-6)11(8,9)10/h2-5H,1H3,(H,8,9,10) Key: JOXIMZWYDAKGHI-UHFFFAOYAG
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 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.

History

Safety

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:

• Acetalization of an aldehyde.^[6]
• Esterification of carboxylic acids.^[7]
• Transesterification of an ester.^[8]

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.

Reactions

• 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

• Tosyl
• Collidine p-toluenesulfonate

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