What Is Toluene Sulfonic Acid?
Toluene sulfonic acid is an aromatic sulfonic acid with the chemical formula C7H8O3S.
Toluenesulfonic acid has a structure in which one hydrogen in the aromatic ring of toluene is replaced by a sulfonic acid. In principle, there are three isomers: o-toluene sulfonic acid, m-toluene sulfonic acid, and p-toluene sulfonic acid, but since toluene is o (ortho) and p (para) oriented, and the ortho form has significant steric hindrance, p-toluene sulfonic acid is generally referred to. p-toluenesulfonic acid.
In the following, unless otherwise noted, p-toluene sulfonic acid is used.
Tosic acid is commonly known as “tosyl acid,” and its abbreviations include PTSA, TSA, and TsOH. Because of its tidal solubility and tendency to absorb moisture, toluene sulfonic acid is often sold commercially as monohydrate.
CAS registration numbers are 104-15-4 (anhydrous) and 6192-52-5 (monohydrate). It has a molecular weight of 172.20 and a melting point of 106-107℃ (anhydrous)/103-106℃ (monohydrate), and is a colorless or white solid at room temperature.
It is soluble in water, ethanol, and ether. Since it is tidally soluble and is altered by light, care should be taken when storing it to keep it away from sunlight and moisture.
Uses of Toluene Sulfonic Acids
Toluene sulfonic acid is widely used in the field of synthetic chemistry as a raw material for synthesis of pharmaceuticals, intermediates for agrochemicals, dyes, and paints, as a raw material for resin curing agents, and as a general purpose acid catalyst.
It also acts as a surfactant because it has both hydrophilic (sulfonic acid) and hydrophobic (toluene) groups. Used as a solubilizer in synthetic detergents, toluene sulfonic acid helps ingredients mix evenly and improves formulation stability.
Characteristics of Toluene Sulfonic Acids
Aqueous solutions of toluene sulfonic acid are highly acidic. p-toluene sulfonic acid has an acid dissociation constant pKa of -2.8. In organic synthesis, p-toluene sulfonic acid is widely used as an acid catalyst because it is a strong acid that is soluble in organic solvents and the anion of the conjugate base has a low nucleophilic property.
When phosphorus pentachloride is applied to the sodium salt of p-toluene sulfonic acid, paratoluene sulfonyl chloride is obtained. Nucleophilic substitution of the hydroxy group of an alcohol may be achieved by converting the hydroxy group to a paratoluenesulfonic acid ester (tosylate) and then applying a nucleophile to replace the tosyl group with the desired nucleophile.
This is because the paratoluenesulfonate anion is an excellent leaving group.
Types of Toluene Sulfonic Acids
Toluene sulfonic acid is available in three types: o-toluene sulfonic acid, m-toluene sulfonic acid, and p-toluene sulfonic acid. o-toluene sulfonic acid and m-toluene sulfonic acid are only slightly distributed, with p-toluene sulfonic acid being the most common. Products include reagents for research and development and industrial chemicals.
The R&D reagent product is sold primarily as p-toluene sulfonic acid monohydrate. The capacities include 25 g, 100 g, 500 g, 1 kg, and 5 kg, and are offered in capacities that are easy to handle in the laboratory.
Industrial chemicals include monohydrate (solid), aqueous solutions (e.g. 70%), and methanol and ether solutions. Solid products are available in capacities of 20 kg (paper bags), 60 kg (drums), 200-230 kg (flexible container bags), etc. Liquid products are offered in tanker trucks, containers, chemical drums, etc. These products are offered in large capacities to meet the needs of factories and other facilities.
Other Information on Toluene Sulfonic Acid
Synthesis of Toluene Sulfonic Acid
Toluene sulfonic acid is synthesized by sulfonation of toluene with concentrated sulfuric acid or fuming sulfuric acid. The main product is the para form, but the ortho form, a byproduct, is the raw material for saccharin. The main impurities are benzene sulfonic acid and sulfuric acid.