Aromatic hydrocarbon

The aromatic hydrocarbon means a closed chain hydrocarbon having a basic structure of a benzene ring or having an aromatic compound property. It can be divided into monocyclic aromatic hydrocarbons, polycyclic aromatic hydrocarbons and non-benzene aromatic hydrocarbons. The monocyclic aromatic hydrocarbon molecule contains only one benzene ring, such as toluene, xylene, ethylbenzene, styrene, phenylacetylene and the like. The polycyclic aromatic hydrocarbon molecule contains two or more benzene rings. According to the way in which the benzene rings are linked to each other, they can be further divided into: 1 polyphenylene aliphatic hydrocarbons such as diphenylmethane, triphenylmethane, stilbene, tetrastyrene and the like. 2 biphenyl and biphenyl, such as biphenyl, terphenyl, biphenyl and so on. 3 fused ring aromatic hydrocarbons, such as naphthalene, anthracene, phenanthrene, anthracene, anthracene, anthracene, anthracene Non-benzene aromatic hydrocarbons do not contain a benzene ring, but have a certain degree of aromatic hydrocarbons such as hydrazine, olefin, and the like. It is easy to initiate a substitution reaction, it is not easy to initiate an addition reaction, and the ring is not easily broken. Aromatic hydrocarbons in nature are mainly obtained from fractions of coal tar and aromatization products of petroleum. The main component of coal tar is aromatic hydrocarbons; the main components of various petroleum crude oils are aliphatic hydrocarbons, and aromatic hydrocarbons only account for 0.2% to 7.4%, but the acute and chronic toxicity of petroleum is mainly aromatic hydrocarbons, especially soluble aromatic hydrocarbons such as naphthalene and phenanthrene. Caused by etc. Can be used as a solvent and chemical raw materials. Benzene is the most basic structure in aromatic hydrocarbons. It usually adopts a structural formula containing three conjugated double bonds and six-membered rings. This was proposed by the German chemist FA Kaikole in 1865 and is called Kaikool. In terms of composition, benzene is an unsaturated hydrocarbon, but it is less prone to addition and oxidation reactions, is prone to substitution reactions, and has special toughness (see "aromaticity"). According to the hybrid orbital theory, each carbon atom in the benzene molecule is sp2 hybridized, and each sp2 hybrid orbit overlaps with the sp2 hybrid orbital of two adjacent carbon atoms to form a C-Cσ bond (see Figure 1), and a sp2 hybrid orbital overlaps with the 1s orbital of a hydrogen atom to form a C-Hσ bond. The simplest aromatic hydrocarbon is benzene. Benzene and other aromatic compounds were originally found in coal tar, so coal tar was the main source of aromatics for a long period of time. However, the coal tar yield is only 3% of coal, and the crude product of various aromatic compounds in coal tar is only 0.3% of coal. Therefore, since the 1940s, aromatic hydrocarbons have been mainly produced from processed petroleum. The aromatic hydrocarbons are all liquid or solid. Insoluble in water, soluble in organic solvents. It has aromaticity, is not easy to react, and is easy to replace. It is stable to heat and oxidant. Aromatic hydrocarbons (especially monocyclic aromatic hydrocarbons) are important chemical raw materials (such as para-xylene is the raw material for making polyester), and many liquid aromatic hydrocarbons can be used as solvents (such as paints are easily soluble in aromatic hydrocarbons). However, when liquid aromatic hydrocarbons come into contact with the skin repeatedly, dermatitis may be caused by dehydration and defatting. The stimulating effect of aromatic hydrocarbon vapor on mucous membrane is stronger than that of aliphatic hydrocarbon, especially benzene vapor has special damage to hematopoietic function. However, animal tests have shown that alkylbenzene does not have this damaging effect.