Chemistry:P-Toluenesulfonic acid
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 Slightly impure sample of the monohydrate
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| Preferred IUPAC name
4-Methylbenzene-1-sulfonic acid | |||
| Other names
4-Methylbenzenesulfonic acid
Tosylic acid Tosic acid para-Toluenesulfonic acid PTSA pTsOH TsOH | |||
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3D model (JSmol)
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| 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 | 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 | ||
| 67 g/100 mL | |||
| Acidity (pKa) | −2.8 (water) reference for benzenesulfonic acid,[3] 8.5 (acetonitrile)[4] | ||
| Structure | |||
| tetrahedral at S | |||
| Hazards | |||
| Main hazards | skin irritant | ||
| Safety data sheet | External MSDS | ||
| GHS pictograms | 
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| GHS Signal word | Warning | ||
| Related compounds | |||
Related sulfonic acids
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Benzenesulfonic acid Sulfanilic acid | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |||
 verify (what is   ?)
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| Infobox references | |||
p-Toluenesulfonic acid (PTSA, pTSA, or pTsOH) or tosylic acid (TsOH) is an organic compound with the formula CH3C6H4SO3H. It is a white extremely hygroscopic solid that is soluble in water, alcohols, and other polar organic solvents.[6] 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.[6]
As with other aryl sulfonic acids, TsOH is a strong organic acid. It is about one million times stronger than benzoic acid.[6] It is one of the few strong acids that is solid and therefore is conveniently weighed and stored.
Preparation and uses
TsOH is prepared on an industrial scale by the sulfonation of toluene. Common impurities include benzenesulfonic acid and sulfuric acid. TsOH monohydrate contains an amount of water. To estimate the total moisture present as impurity, the Karl Fischer method is used.[citation needed] 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" strong acid. Examples of uses include:
- Acetalization of an aldehyde.[7]
- Fischer–Speier esterification[8]
- Transesterification reactions[9]
Tosylates
Alkyl tosylates are alkylating agents because tosylate is electron-withdrawing as well as 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 times faster than the solvolysis of anti-7-norbornyl p-toluenesulfonate.[10]
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.[11]
Reactions
- TsOH may be converted to p-toluenesulfonic anhydride by heating with phosphorus pentoxide.[12]
- When heated with acid and water, TsOH undergoes hydrolysis to toluene:
- CH3C6H4SO3H + H2O → C6H5CH3 + H2SO4
This reaction is general for aryl sulfonic acids.[13][14]
See also
References
- ↑ Merck Index, 11th Edition, 9459.
- ↑ 2.0 2.1 2.2 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: pKa 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
- ↑ GHS: GESTIS 510754
- ↑ 6.0 6.1 6.2 Baghernejad, Bita (31 August 2011). "Application of p-toluenesulfonic Acid (PTSA) in Organic Synthesis". Current Organic Chemistry 15 (17): 3091–3097. 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. http://www.orgsyn.org/demo.aspx?prep=v77p0236.; Collective Volume, 10, pp. 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. http://www.orgsyn.org/demo.aspx?prep=cv9p0722.; Collective Volume, 9, pp. 722
- ↑ Imwinkelried, R.; Schiess, M.; Seebach, D. (1993). "Diisopropyl (2S,3S)-2,3-O-isopropylidenetartrate". Organic Syntheses. http://www.orgsyn.org/demo.aspx?prep=cv8p0201.; Collective Volume, 8, pp. 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". http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch08/ch8-10-1.html.
- ↑ L. Field; J. W. McFarland (1963). "p-Toluenesulfonic Anhydride". Organic Syntheses. http://www.orgsyn.org/demo.aspx?prep=cv4p0940.; Collective Volume, 4, pp. 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. https://zenodo.org/record/1901301.
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