What Is a Sulfuric Acid Catalyst?

A sulfuric acid catalyst is the chemical compound containing hydrogen, sulfur and oxygen, with the molecular formula H₂SO₄, and although it is present only in trace amounts, dramatically helps speed up a reaction by lowering its activation energy. Sulfuric acid is one of the world's most widely produced chemicals, and when used as a catalyst, it can bring about chemical reactions even when used in small amounts. It is often used a generic acid catalyst for the manufacture of a wide variety of products, including plastics, fuels and clothing.

In general, a catalyst is any type of molecule that helps speed up a reaction without being consumed. Often, only small amounts are needed to bring about reactions that would either be difficult or impossible to otherwise perform. Catalysts such as sulfuric acid lower the activation energy of a reaction by providing new intermediate states by which a reaction can proceed. Sulfuric acid can do this because it is a strong acid that can donate protons to reactants, allowing reactants to form positively charged ions, otherwise known as cations. In the process, sulfuric acid becomes a negatively charged ion, which further helps stabilize the positively charged reactants, allowing them to undergo other desirable reactions.

Sulfuric acid catalysts are used in many important industrial manufacturing processes. In one noteworthy reaction, a sulfuric acid catalyst is used in the production of nylon. Nylon, a versatile material that is used to make clothing and fabrics, is synthesized from monomers of caprolactam. Caprolactam, in turn, is produced when cyclohexanone oxime undergoes what is known as a Beckmann rearrangement in the presence of a sulfuric acid catalyst. The catalyst donates a proton to cyclahexanone oxime, which lowers the energy of the reaction intermediate and allows the molecule to rearrange its atoms to give the monomer of nylon.

A sulfuric acid catalyst also is used in producing fuel additives for gasoline. Isooctane is one important additive that is frequently combined with gasoline to increase the octane rating of motor fuel. The petroleum industry produces isooctane by combining isobutylene and isobutane in the presence of a sulfuric acid catalyst. Once again, sulfuric acid helps create lower-energy reaction intermediates by donating protons to help bring about the synthesis.

Sulfuric acid catalysts are often chosen because of their price, availability and convenience, because any generic acid catalyst can be used in the reaction. The first chemical of choice is often sulfuric acid, because it is cheap and because it is one of the world's most widely available chemicals. Originally known as oil of vitriol, sulfuric acid was one of the first chemicals to be discovered and purified. Sulfuric acid can now be found in the inventory of virtually every laboratory and chemicals factory in the world.