p-Toluenesulfonic Acid

(monohydrate) [104-15-4] C7H8O3S (MW 172.22) (Na salt) [6192-52-5] C7H10O4S (MW 190.24) [657-84-1] C7H7NaO3S (MW 194.20) (acid catalyst frequently used in nonpolar media; effective in carbonyl protection–deprotection; selectively cleaves N-Boc, other amine protecting groups; superior for enol ether, acetate preparation; used in esterifications, dehydrations, isomerizations, rearrangements) Alternate Name: tosic acid. Physical Data: the anhydrous acid exists as monoclinic leaflets or prisms, mp 106–107 °C; pKa −6.62 (H2SO4).1 There is also a metastable form, mp 38 °C. The monohydrate is a white crystalline powder, mp 103–106 °C. Solubility: sol water (67 g/100 mL), ethanol, ethyl ether. The sodium salt is very sol water. Form Supplied in: widely available as the monohydrate, which is commonly used. Various metal salts are also commercially available. Analysis of Reagent Purity: by acid–base titrimetry.46 Purification: precipitated or crystallized from HCl soln, aq EtOH; the free acid has been crystallized from several organic solvents.47 Handling, Storage, and Precautions: highly toxic, oxidizing agent. Extremely irritating to the skin and mucous membranes. Use of gloves and protective clothing is recommended.2 Use in a fume hood.