Thiophene compound

The thiophene compound is a compound in which the basic skeleton of a five-membered heterocyclic compound containing only one sulfur atom is thiophene, and thiophene is present in coal tar and shale oil. Thiophene is more active than benzene; it has photosensitivity, carbon framework rearrangement during illumination; it can react with metal; sulfur on thiophene ring can be removed under the action of ruthenium nickel; substitution reaction can occur (more in 2 positions) ); can be oxidized and ring-opened, different oxidants can obtain different products; can be nitrated at 2, 5 positions to form nitrothiophene; can be halogenated to form 2-position monohalide, 2,5-position dihalide, 2 , 3,5-trihalide and tetrahalide; condensed with benzene to form benzothiophene. The thiophene ring has an aromatic nature because the unshared electron pair of sulfur forms a 6π electron system together with two carbon-carbons. Therefore, an electrophilic substitution reaction such as nitration, sulfonation or halogenation can be carried out. The positions to be replaced are 2-position and 5-position. The electrophilic substitution reaction of thiophene is much easier than benzene. For example, a thiophene can undergo a Friedel-Crafts reaction in the presence of a mild oxidizing agent such as orthophosphoric acid, and an acyl group is introduced at the α-position. In the presence of nitric acid, thiophene is reacted with iodine to obtain 2-iodothiophene in a relatively high yield. Alternatively, 2-thienylmethylamine can be easily obtained by using a Mannich reaction. Thiophene can be used in the production of various dyes, fragrances, quenching and rapid-heating plastics, high-activity solvents, irritants, insecticides, brighteners, cosmetics and bioactive substances, as well as vitamins, anesthetics and antibiotics. Although thiophene can be synthesized by chemical methods, the cost is too high. Thiophene is mainly present in light benzene obtained by pre-rectification of crude benzene. When the light benzene is hydrorefined, the thiophene is destroyed. When the light benzene acid is washed and refined, most of the thiophene and the unsaturated compound are polymerized into a tar-like substance, and only a small amount of thiophene reacts with sulfuric acid to form a thiophenesulfonic acid which is easy to extract. The production of thiophene is greatly reduced. In the light benzene acid washing and purification, thiophene is reacted with sulfuric acid to form thiophene sulfonic acid dissolved in waste sulfuric acid, the waste sulfuric acid is clarified, the tar-like substance is removed, and then hydrolyzed. The distillate is cooled and separated by condensation to obtain a crude oil containing thiophene and a benzene hydrocarbon. After the crude oil is neutralized to neutral or slightly alkaline by a base, it is rectified by a rectification column having a theoretical number of plates of 30 to 40 to obtain a thiophene product containing more than 90% of thiophene. The middle distillate cut during rectification is concentrated and refluxed into the crude oil. When the thiophene is completely distilled off, the raffinate can also rectify the meta-xylene product containing about 95% of m-xylene.