p-Toluenesulfonic acid monohydrate

White crystals

p-Toluenesulfonic acid monohydrate (p-TsOH·H₂O) may be used as a catalyst in the synthesis of the following:

• Unsymmetrical benzils.
• Highly substituted piperidines.
• 1,3,5-Trisubstituted benzenes by trimerization of alkynes.
• Triazoloquinazolinone and benzimidazoquinazolinone derivatives.
• 1,3,5-Trisubstituted pyrazoles derivatives.
• Selenated ketene dithioacetals.

Derivitizing agent.

p-Toluenesulfonic acid monohydrate is used as a catalyst in the synthesis of resveratrol, in oxane derivatives as an antimalarial agent, as substituted piperidine and unsymmetrical benzyl. It acts as a catalyst in the preparation of 1,3,5-trisubstituted pyrazoles derivatives, selenated ketene dithioacetals, triazoloquinazolinone and benzimidazoquinazolinone derivatives. It also serves as an intermediate in the esterification and in reductive amination reactions.

p-Toluenesulfonic acid monohydrate, an oxonium salt, is an inexpensive and easy to handle organic catalyst used in organic synthesis. The study of its crystalline structure shows that it is monoclinic with P2₁/c space group. Its solubility in aqueous sulfuric acid solutions has been studied.

Purify the acid by precipitation from a saturated solution at 0o by introducing HCl gas. It can also be crystallised from conc HCl, then crystallised from dilute HCl (charcoal) to remove benzenesulfonic acid. It has been crystallised from EtOH/water. Dry it in a vacuum desiccator over solid KOH and CaCl2. p-Toluenesulfonic acid can be dehydrated by azeotropic distillation with *benzene or by heating at 100o for 4hours under water-pump vacuum. The anhydrous acid can be crystallised from *benzene, CHCl3, ethyl acetate, anhydrous MeOH, or from acetone by adding a large excess of *benzene. It can also be dried under vacuum at 50o. The S-benzylisothiuronium salt has m 182o (from aqueous EtOH). [Beilstein 11 IV 241.]

The initial threshold screening levels (ITSLs) for p-toluenesulfonic acid monohydrate are 1.9 μg/m3, annual averaging time and 230 μg/m3, 1 hour averaging time.