para-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. Buy Phenethyl tosylate (2-phenylethyl 4-methylbenzenesulfonate)

Preparation and uses

TsOH is prepared on an industrial scale by the sulfonation of toluene. Common impurities include benzenesulfonic acid and sulfuric acid. TsOH is most often supplied as the monohydrate, and it may be necessary to remove the complexed water before use. 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 as a leaving group, the 2-norbornyl cation was formed by an elimination reaction of 7-norbornenyl tosylate. The elimination occurs 10¹¹ times faster than the solvolysis of anti-7-norbornyl Para-toluenesulfonate.^[10]

Tosylates are also protecting groups for alcohols. They are prepared by combining the alcohol with 4-toluenesulfonyl chloride in the presence of a base. These reactions are usually performed in an aprotic solvent, often pyridine, which additionally acts as a base.^{[11] Buy Phenethyl tosylate (2-phenylethyl 4-methylbenzenesulfonate)}

Reactions

• TsOH may be converted to para-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

• Tosyl
• Collidinium p-toluenesulfonate

In organic chemistry, a toluenesulfonyl group (tosyl group, abbreviated Ts or Tos^{[nb 1]}) is a univalent functional group with the chemical formula −SO₂−C₆H₄−CH₃. It consists of a tolyl group, −C₆H₄−CH₃, joined to a sulfonyl group, −SO₂−, with the open valence on sulfur. This group is usually derived from the compound tosyl chloride, CH₃C₆H₄SO₂Cl (abbreviated TsCl), which forms esters and amides of toluenesulfonic acid, CH₃C₆H₄SO₂OH (abbreviated TsOH). The para orientation illustrated (p-toluenesulfonyl) is most common, and by convention tosyl without a prefix refers to the p-toluenesulfonyl group.

The tosyl terminology was proposed by German chemists Kurt Hess and Robert Pfleger in 1933 on the pattern of trityl^[1] and adopted in English starting from 1934.^[2]

The toluenesulfonate (or tosylate) group refers to the −O−SO₂C₆H₄CH₃ (–OTs) group, with an additional oxygen attached to sulfur and open valence on an oxygen.^[3] In a chemical name, the term tosylate may either refer to the salts containing the anion of p-toluenesulfonic acid, TsO⁻M⁺ (e.g., sodium p-toluenesulfonate), or it may refer to esters of p-toluenesulfonic acid, TsOR (R = organyl group).

For S_N2 reactions, alkyl alcohols can also be converted to alkyl tosylates, often through addition of tosyl chloride. In this reaction, the lone pair of the alcohol oxygen attacks the sulfur of the tosyl chloride, displacing the chloride and forming the tosylate with retention of reactant stereochemistry. This is useful because alcohols are poor leaving groups in S_N2 reactions, in contrast to the tosylate group. It is the transformation of alkyl alcohols to alkyl tosylates that allows an S_N2 reaction to occur in the presence of a good nucleophile.

A tosyl group can function as a protecting group in organic synthesis. Alcohols can be converted to tosylate groups so that they do not react. The tosylate group may later be converted back into an alcohol. The use of these functional groups is exemplified in organic synthesis of the drug tolterodine, wherein one of the steps a phenol group is protected as its tosylate and the primary alcohol as its nosylate. The latter is a leaving group for displacement by diisopropylamine:^{[4][nb 2]}

The tosyl group is also useful as a protecting group for amines. The resulting sulfonamide structure is extremely stable. It can be deprotected to reveal the amine using reductive or strongly acidic conditions.^[5]

Tosyl (Ts) group is commonly used as a protecting group for amines in organic synthesis.

• Tosyl chloride and pyridine in dichloromethane^[6]

• HBr and acetic acid at 70 °C^[7]
  

  

• Refluxing with TMSCl, sodium iodide and acetonitrile^[8]
• Reduction with SmI₂^[9]
• Reduction with Red-Al^[10]

Closely related to the tosylates are the nosylates and brosylates, which are the abbreviated names for o– or p-nitrobenzenesulfonates and p-bromobenzenesulfonates, respectively.

• Tosylic acid
• Sulfonyl group