p-Toluenesulfonic acid

p-Toluenesulfonic acid[1]
	; Slightly impure sample of the monohydrate
Names
	Preferred IUPAC name 4-Methylbenzene-1-sulfonic acid
	Other names 4-Methylbenzenesulfonic acid; Tosylic acid ; tosic acid; PTSA
Identifiers
CAS Number	104-15-4 ; 6192-52-5 (monohydrate) ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:27849 ;
ChEMBL	ChEMBL541253 ;
ChemSpider	5876 ;
DrugBank	DB03120 ;
ECHA InfoCard	100.002.891
KEGG	C06677 ;
PubChem CID	6101;
UNII	QGV5ZG5741 ; 3BTO78GAFF ((monohydrate) ;
CompTox Dashboard (EPA)	DTXSID0026701 ;
	InChI InChI=1S/C7H8O3S/c1-6-2-4-7(5-3-6)11(8,9)10/h2-5H,1H3,(H,8,9,10) Key: JOXIMZWYDAKGHI-UHFFFAOYSA-N ; 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;
	SMILES Cc1ccc(cc1)S(=O)(=O)O;
Properties
Chemical formula	C7H8O3S
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
Solubility in water	67 g/100 mL
Acidity (pKa)	−2.8 (water) reference for benzenesulfonic acid,[3]; 8.5 (acetonitrile)[4]
Structure
Molecular shape	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R-phrases (outdated)	R36/37/38
S-phrases (outdated)	S26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 CH₃ C₆H₄ SO₃H. It is a white solid that is soluble in water, alcohols, and other polar organic solvents.[5] 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.[5]

As with other sulfonic acids, TsOH is a strong organic acid. It is about one million times stronger than benzoic acid.[5] It is one of the few strong acids that is solid and, hence, conveniently weighed.

Preparation and handling

TsOH is prepared on an industrial scale by the sulfonation of toluene. It is hygroscopic and hydrates readily. Common impurities include benzenesulfonic acid and sulfuric acid. TsOH monohydrate contains crystalline water as well as water as an impurity. To estimate the total moisture present as impurity, the Karl Fischer method is used. 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" acid catalyst. Examples of uses include:

Tosylates

Alkyl tosylates are alkylating agents because tosylate is electron-withdrawing, which makes the tosylate anion 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.

In a famous and illustrative use of tosylate, 2-norbornyl cation was displaced from the 7-norbornenyl tosylate. The elimination occurs 10¹¹ faster than the solvolysis of anti-7-norbornyl p-toluenesulfonate.[9]

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

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.[10]

Reactions

TsOH may be converted to p-toluenesulfonic anhydride by heating with phosphorus pentoxide.[11]
When heated with acid and water, TsOH undergoes hydrolysis to toluene:

CH₃C₆H₄SO₃H + H₂O → C₆H₅CH₃ + H₂SO₄

This reaction is general for aryl sulfonic acids.[12][13]

References

Merck Index, 11th Edition, 9459.
Armarego, W. L. F. (2003). Purification of Laboratory Chemicals (8th ed.). Oxford: Elsevier Science. p. 612. ISBN 978-0-12-805457-4.
Guthrie, J. P. Hydrolysis of esters of oxy acids: pK_a values for strong acids. Can. J. Chem. 1978, 56, 2342-2354.
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
Baghernejad, Bita (31 August 2011). "Application of p-toluenesulfonic Acid (PTSA) in Organic Synthesis". Current Organic Chemistry. 15 (17). doi:10.2174/138527211798357074.
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, 10, p. 577
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, 9, p. 722
Imwinkelried, R.; Schiess, M.; Seebach, D. (1993). "Diisopropyl (2S,3S)-2,3-O-isopropylidenetartrate". Organic Syntheses.; Collective Volume, 8, p. 201
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.
"Nucleophilic Substitution".
L. Field & J. W. McFarland (1963). "p-Toluenesulfonic Anhydride". Organic Syntheses.; Collective Volume, 4, p. 940
C. M. Suter (1944). The Organic Chemistry of Sulfur. New York: John Wiley & Sons. pp. 387–388.
J. M. Crafts (1901). "Catalysis in concentrated solutions". J. Am. Chem. Soc. 23 (4): 236–249. doi:10.1021/ja02030a007.

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[1] Merck Index, 11th Edition, 9459.

[Armarego_2003-2] 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: pK_a 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

[Baghernejad_2011-5] Baghernejad, Bita (31 August 2011). "Application of p-toluenesulfonic Acid (PTSA) in Organic Synthesis". Current Organic Chemistry. 15 (17). doi:10.2174/138527211798357074.

[6] 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, 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". Organic Syntheses.; Collective Volume, 9, p. 722

[8] Imwinkelried, R.; Schiess, M.; Seebach, D. (1993). "Diisopropyl (2S,3S)-2,3-O-isopropylidenetartrate". Organic Syntheses.; Collective Volume, 8, p. 201

[:0-9] 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.

[10] "Nucleophilic Substitution".

[11] L. Field & J. W. McFarland (1963). "p-Toluenesulfonic Anhydride". Organic Syntheses.; Collective Volume, 4, p. 940

[12] C. M. Suter (1944). The Organic Chemistry of Sulfur. New York: John Wiley & Sons. pp. 387–388.

[13] J. M. Crafts (1901). "Catalysis in concentrated solutions". J. Am. Chem. Soc. 23 (4): 236–249. doi:10.1021/ja02030a007.

p-Toluenesulfonic acid

Preparation and handling

Tosylates

Reactions

See also

References