Sulfonic acid in the context of Organic acid anhydride

An organic acid is an organic compound with acidic properties. The most common organic acids are the carboxylic acids, whose acidity is associated with their carboxyl group –COOH. Sulfonic acids, containing the group –SO₂OH, are relatively stronger acids. Alcohols, with –OH, can act as acids but they are usually very weak. The relative stability of the conjugate base of the acid determines its acidity. Other groups can also confer acidity, usually weakly: the thiol group –SH, the enol group, and the phenol group. In biological systems, organic compounds containing these groups are generally referred to as organic acids.

Taurine (/ˈtɔːriːn/ ; IUPAC: 2-aminoethanesulfonic acid) is a naturally occurring organic compound with the chemical formula C₂H₇NO₃S, and is a non-proteinogenic amino sulfonic acid widely distributed in mammalian tissues and organs. Structurally, by containing a sulfonic acid group instead of a carboxylic acid group, it is not involved in protein synthesis but is still usually referred to as an amino acid. As non-proteinogenic amino sulfonic acid, it is not encoded by the genetic code and is distinguished from the protein-building α-amino acids.

In chemistry, an acyl group is a moiety derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids. It contains a double-bonded oxygen atom and an organyl group (R−C=O) or hydrogen in the case of formyl group (H−C=O). In organic chemistry, the acyl group (IUPAC name alkanoyl if the organyl group is alkyl) is usually derived from a carboxylic acid, in which case it has the formula R−C(=O)−, where R represents an organyl group or hydrogen. Although the term is almost always applied to organic compounds, acyl groups can in principle be derived from other types of acids such as sulfonic acids and phosphonic acids. In the most common arrangement, acyl groups are attached to a larger molecular fragment, in which case the carbon and oxygen atoms are linked by a double bond.

In organosulfur chemistry, a sulfonate is a salt, anion or ester of a sulfonic acid. Its formula is R−S(=O)₂−O, containing the functional group −S(=O)₂−O, where R is typically an organyl group, amino group or a halogen atom. Sulfonates are the conjugate bases of sulfonic acids. Sulfonates are generally stable in water, non-oxidizing, and colorless. Many useful compounds and even some biochemicals feature sulfonates. Most detergents and surfactants are sulfonates. These include alkylbenzene sulfonates, 𝛼-Olefin sulfonates, and paraffin sulfonates.

In organic chemistry, the sulfonamide functional group (also spelled sulphonamide) is an organosulfur group with the structure R−S(=O)₂−NR₂. It consists of a sulfonyl group (O=S=O) connected to an amine group (−NH₂). Relatively speaking this group is unreactive. Because of the rigidity of the functional group, sulfonamides are typically crystalline; for this reason, the formation of a sulfonamide is a classic method to convert an amine into a crystalline derivative which can be identified by its melting point. Many important drugs contain the sulfonamide group.

A sulfonamide (compound) is a chemical compound that contains this group. The general formula is R−SO₂NR'R" or R−S(=O)₂−NR'R", where each R is some organic group; for example, "methanesulfonamide" (where R = methane, R' = R" = hydrogen) is CH₃SO₂NH₂. Any sulfonamide can be considered as derived from a sulfonic acid by replacing a hydroxyl group (−OH) with an amine group.

An organic acid anhydride is an acid anhydride that is also an organic compound. An acid anhydride is a compound that has two acyl groups bonded to the same oxygen atom. A common type of organic acid anhydride is a carboxylic anhydride, where the parent acid is a carboxylic acid, the formula of the anhydride being (RC(O))₂O. Symmetrical acid anhydrides of this type are named by replacing the word acid in the name of the parent carboxylic acid by the word anhydride. Thus, (CH₃CO)₂O is called acetic anhydride. Mixed (or unsymmetrical) acid anhydrides, such as acetic formic anhydride (see below), are known, whereby reaction occurs between two different carboxylic acids. Nomenclature of unsymmetrical acid anhydrides list the names of both of the reacted carboxylic acids before the word "anhydride" (for example, the dehydration reaction between benzoic acid and propanoic acid would yield "benzoic propanoic anhydride").

One or both acyl groups of an acid anhydride may also be derived from another type of organic acid, such as sulfonic acid or a phosphonic acid. One of the acyl groups of an acid anhydride can be derived from an inorganic acid such as phosphoric acid. The mixed anhydride 1,3-bisphosphoglyceric acid, an intermediate in the formation of ATP via glycolysis, is the mixed anhydride of 3-phosphoglyceric acid and phosphoric acid. Acidic oxides are also classified as acid anhydrides.

Perfluorobutanesulfonic acid (PFBS) is a PFAS chemical compound having a four-carbon fluorocarbon chain and a sulfonic acid functional group. It is stable and unreactive because of the strength of carbon–fluorine bonds. It can occur in the form of a colorless liquid or solid. Its conjugate base is perfluorobutanesulfonate (also called nonaflate) which functions as the hydrophobe in fluorosurfactants.

Since June 2003, 3M has used PFBS as a replacement for the persistent, toxic, and bioaccumulative compound perfluorooctanesulfonic acid (PFOS) in its Scotchgard stain repellents.