Aromatic sulfonation is an

organic reaction Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, Mechanistic Organ ...

in which a hydrogen atom on an

arene Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past grouping ...

is replaced by a

sulfonic acid In organic chemistry, sulfonic acid (or sulphonic acid) refers to a member of the class of organosulfur compounds with the general formula , where R is an organic alkyl or aryl group and the group a sulfonyl hydroxide. As a substituent, it is kn ...

functional group In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest ...

in an

electrophilic aromatic substitution Electrophilic aromatic substitution is an organic reaction in which an atom that is attached to an aromatic system (usually hydrogen) is replaced by an electrophile. Some of the most important electrophilic aromatic substitutions are aromatic ni ...

. Aryl sulfonic acids are used as

detergent A detergent is a surfactant or a mixture of surfactants with cleansing properties when in dilute solutions. There are a large variety of detergents, a common family being the alkylbenzene sulfonates, which are soap-like compounds that are more ...

dye A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution an ...

, and

drug A drug is any chemical substance that causes a change in an organism's physiology or psychology when consumed. Drugs are typically distinguished from food and substances that provide nutritional support. Consumption of drugs can be via insuffla ...

Stoichiometry and mechanism

Typical conditions involve heating the aromatic compound with sulfuric acid: :C₆H₆ + H₂SO₄ → C₆H₅SO₃H + H₂O

Sulfur trioxide Sulfur trioxide (alternative spelling sulphur trioxide, also known as ''nisso sulfan'') is the chemical compound with the formula SO3. It has been described as "unquestionably the most important economically" sulfur oxide. It is prepared on an ind ...

or its protonated derivative is the actual

electrophile In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carries ...

in this electrophilic aromatic substitution. To drive the equilibrium, dehydrating agents such as

thionyl chloride Thionyl chloride is an inorganic compound with the chemical formula . It is a moderately volatile, colourless liquid with an unpleasant acrid odour. Thionyl chloride is primarily used as a chlorinating reagent, with approximately per year bein ...

can be added. :C₆H₆ + H₂SO₄ + SOCl₂ → C₆H₅SO₃H + SO₂ + 2 HCl

Chlorosulfuric acid Chlorosulfuric acid (IUPAC name: sulfurochloridic acid) is the inorganic compound with the formula HSO3Cl. It is also known as chlorosulfonic acid, being the sulfonic acid of chlorine. It is a distillable, colorless liquid which is hygroscopic and ...

is also an effective agent: :C₆H₆ + HSO₃Cl → C₆H₅SO₃H + HCl In contrast to

aromatic nitration In organic chemistry, nitration is a general class of chemical processes for the introduction of a nitro group into an organic compound. The term also is applied incorrectly to the different process of forming nitrate esters between alcohols and ...

and most other electrophilic aromatic substitutions this reaction is reversible. Sulfonation takes place in concentrated acidic conditions and desulfonation is the mode of action in a dilute hot aqueous acid. The reaction is very useful in protecting the aromatic system because of this reversibility. Due to their electron withdrawing effects, sulfonate protecting groups can be used to prevent electrophilic aromatic substitution. They can also be installed as directing groups to affect the position where a substitution may take place.T.W> Graham Solomons: ''Organic Chemistry'', 11th Edition, Wiley, Hoboken, NJ, 2013, p. 676, .

Specialized sulfonation methods

Many method have been developed for introducing sulfonate groups aside from direction sulfonation.

Piria reaction

A classic named reaction is the Piria reaction (

Raffaele Piria Raffaele Piria (Scilla 20 August 1814 – Turin 18 July 1865) was an Italian chemist from Scilla, who lived in Palmi. He converted the substance Salicin into a sugar and a second component, which on oxidation becomes salicylic acid, a major comp ...

, 1851) in which

nitrobenzene Nitrobenzene is an organic compound with the chemical formula C6H5 NO2. It is a water-insoluble pale yellow oil with an almond-like odor. It freezes to give greenish-yellow crystals. It is produced on a large scale from benzene as a precursor t ...

is reacted with a metal

bisulfite The bisulfite ion (IUPAC-recommended nomenclature: hydrogensulfite) is the ion . Salts containing the ion are also known as "sulfite lyes". Sodium bisulfite is used interchangeably with sodium metabisulfite (Na2S2O5). Sodium metabisulfite disso ...

forming an aminosulfonic acid as a result of combined

nitro group reduction The reduction of nitro compounds are chemical reactions of wide interest in organic chemistry. The conversion can be effected by many reagents. The nitro group was one of the first functional groups to be reduced. Alkyl and aryl nitro compounds ...

and sulfonation. Piria reaction

Tyrer sulfonation process

In the Tyrer sulfonation process (1917), at some time of technological importance, benzene vapor is led through a vessel containing 90% sulfuric acid the temperature of which is increased from 100 to 180°C. Water and benzene are continuously removed in a condenser and the benzene layer fed back to the vessel. In this way an 80% yield is obtained. Amino Sulfonic Acid Synthesis V

Applications

Aromatic sulfonic acids are intermediates in the preparation of

s and many pharmaceuticals. Sulfonation of

aniline Aniline is an organic compound with the formula C6 H5 NH2. Consisting of a phenyl group attached to an amino group, aniline is the simplest aromatic amine In organic chemistry, an aromatic amine is an organic compound consisting of an aroma ...

s lead to a large group of sulfa drugs. Allura Red AC Structural Formula V1

Sulfonation of

polystyrene Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is a ...

is used to make

sodium polystyrene sulfonate Polystyrene sulfonates are a group of medications used to treat high blood potassium. Effects generally take hours to days. They are also used to remove potassium, calcium, and sodium from solutions in technical applications. Common side effects ...

, a common ion exchange resin for

water softening Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting soft water requires less soap for the same cleaning effort, as soap is not wasted bonding with calcium ions. Soft water also exten ...

Reactions of aryl sulfonic acids

As a

, aryl sulfonic acids undergo desulfonation when heated in water: :RC₆H₄SO₃H + H₂O → RC₆H₅ + H₂SO₄ When treated with strong base, benzenesulfonic acid derivatives convert to phenols. :C₆H₅SO₃H + 2 NaOH → C₆H₅OH + Na₂SO₄ + H₂O

References

{{DEFAULTSORT:Aromatic Sulfonation Substitution reactions