p-Toluenesulfonic acid

p-Toluenesulfonic acid

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Names
IUPAC name 4-methylbenzenesulfonic acid
Other names Tosylic acid tosic acid PTSA
Identifiers
CAS Number	104-15-4 Y 6192-52-5 (monohydrate) N
ChEBI	CHEBI:27849 N
ChEMBL	ChEMBL541253 Y
ChemSpider	5876 Y
DrugBank	DB03120 N
Jmol 3D model	Interactive image
KEGG	C06677 Y
PubChem	6101
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
SMILES Cc1ccc(cc1)S(=O)(=O)O
Properties
Chemical 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 (100 °F; 311 K) (anhydrous) 103 to 106 °C (217 to 223 °F; 376 to 379 K) (monohydrate)
Boiling point	140 °C (284 °F; 413 K) at 20 mmHg
Solubility in water	67 g/100 mL
Acidity (pKa)	−2.8 (water), 8.5 (acetonitrile)
Structure
Molecular shape	tetrahedral at S
Vapor pressure	{{{value}}}
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).
N verify (what is YN ?)
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.

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

• Acetalization of an aldehyde.
• Esterification of carboxylic acids.
• Transesterification of an ester.

Tosylate esters

File:Tosylate-3D-balls.png

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. 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

• TsOH may be converted to p-toluenesulfonic anhydride by heating with phosphorus pentoxide.
• When TsOH is heated with acid and water, a hydrolysis reaction takes place and toluene is formed:

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.

See also

• Tosyl
• Collidinium p-toluenesulfonate