Here is an article that I hope will be helpful to the landlord-the nature, application, harm and prevention of benzene and its derivatives. In the early18th century, when gas was used as lighting gas, Kekule's swing double bond benzene was synthesized for the first time. 1803-1819g.t. accum produced many products by the same method, and some samples were detected with a small amount of benzene by modern analytical methods. But it is generally believed that benzene was discovered by michael faraday in 1825. He separated high-purity benzene from the pyrolysis products of fish oil and other similar substances, which was called "double carburet of hydrogen". Some physical properties and chemical composition of benzene were determined, and the hydrocarbon ratio of benzene molecule was expounded. 1833, Milscherlich determined the empirical formula (C6H6) of six carbons and six hydrogen atoms in benzene molecule. 1865, Friedrich Kekule proposed the structure of alternating single and double bonds of benzene ring and infinite * * * yoke, which is now called Kekule type. This structure also explains that the position of the double bond in the ring is not fixed and can move quickly, so six carbons are equivalent. By studying the types of monochlorobenzene and dichlorobenzene, he found that benzene is a cyclic structure, and each carbon is connected with a hydrogen. Others put forward other ideas: james dewar summed up different structures; Dewar benzene named after it has been proved to be another substance different from benzene, which can be obtained from benzene by illumination. 1845, German chemist Hoffman discovered benzene from the light fraction of coal tar, and his student C Mansfield subsequently processed and purified it. Later, he invented crystallization to refine benzene. He also conducted industrial application research, which opened a way for the processing and utilization of benzene. The industrial production of benzene started from 1865. It was originally recovered from coal tar. With the expansion of applications, the output is rising, and 1930 has become one of the top ten tonnage products in the world. In 1960s, Chinese scientists used synthetic technology to produce synthetic benzene, and the first synthetic benzene workshop was built in Shanghai on 1966. Shanghai researchers, after repeated experiments and using their own technical route, successfully synthesized benzene and built the first benzene synthesis workshop in China. Later, due to the high production cost, this method was abandoned. The preparation source is obtained by partial extraction and fractionation of coke oven gas (coal gas) and coal tar light oil. It can also be prepared by dehydrogenation of cyclohexane or disproportionation of toluene or by hydrodemethylation of xylene and steam demethylation. Physical Properties Benzene has a boiling point of 80. 1℃ and a melting point of 5.5℃. At room temperature, it is a colorless, fragrant and transparent liquid, which is volatile. The density of benzene is lower than that of water, with a density of 0.88g/ml, but its molecular weight is heavier than that of water. Benzene is insoluble in water, and 1.7g benzene can be dissolved in 1 liter of water at most; However, benzene is a good organic solvent, and it has strong solubility for organic molecules and some nonpolar inorganic molecules. Benzene can react with water to form azeotrope with boiling point of 69.25℃ and benzene content of 9 1.2%. Therefore, benzene distillation is often added in the reaction of generating water to take it out. Aromatic hydrocarbons with the simplest chemical properties. The molecular formula is C6H6. It is one of the basic raw materials of organic chemical industry. Colorless, flammable and odorous liquid. The melting point is 5.5℃, the boiling point is 80.65438 0℃, and the relative density is 0.8765 (20/4℃). Almost insoluble in water, it can be mixed with organic solvents such as ethanol, ether and carbon disulfide. It can form an azeotropic mixture with water, with a boiling point of 69.25℃ and a benzene content of 9 1.2%. Therefore, benzene distillation is often added in the reaction of generating water to take it out. When benzene burns, it produces thick smoke. Benzene can undergo substitution, addition and oxidation reactions. Benzene is nitrated with a mixture of nitric acid and sulfuric acid to produce nitrobenzene, and nitrobenzene is reduced to produce aniline, which is an important dye intermediate. Benzene is sulfonated with sulfuric acid to produce benzene sulfonic acid, which can be used to synthesize phenol; Benzene reacts with chlorine in the presence of ferric chloride to produce chlorobenzene, which is an important intermediate. Benzene reacts with ethylene, propylene or long-chain olefins in the presence of anhydrous aluminum trichloride and other catalysts to produce ethylbenzene, cumene or alkylbenzene. Ethylbenzene is the raw material for synthesizing styrene, cumene is the raw material for synthesizing phenol and acetone, and alkylbenzene is the raw material for synthesizing detergent. Catalytic hydrogenation of benzene to cyclohexane is the raw material for synthesizing nylon. Insecticide 666 can be obtained by adding three molecules of chlorine to benzene under illumination. Because it is toxic to people and animals, its production and use have been banned. Benzene is difficult to be oxidized, but in the presence of vanadium oxide, it can be oxidized to maleic anhydride at 450℃, which is the raw material for synthesizing unsaturated polyester resin. Benzene is a good solvent for rubber, fat and many resins, but it has been gradually replaced by other solvents because of its high toxicity. Benzene can be added to gasoline to improve its antiknock performance. Benzene is produced industrially by catalytic reforming of naphtha fraction from petroleum refining, or recovered from coking coke oven gas. Benzene vapor is toxic, which can cause convulsion and even unconsciousness when acute poisoning is serious; Chronic poisoning can damage hematopoietic function. In 1865, F.A. Kekule proposed the cyclic structural formula of benzene, which is still in use today. According to the description of quantum chemistry, as a whole, six π electrons in benzene molecule are distributed above and below the torus. Therefore, in recent years, the structure of benzene is also expressed by the formula +0b in Figure 65438. Benzene is a colorless liquid with a special aromatic smell. It is miscible with alcohol, ether, acetone and carbon tetrachloride and slightly soluble in water. Benzene is volatile and flammable, and its vapor is explosive. Frequent exposure to benzene can make the skin dry and desquamate due to degreasing, and allergic eczema appears in some cases. Long-term inhalation of benzene can cause aplastic anemia. Benzene molecules have a planar regular hexagonal structure. Each bond angle is 120, and the bond length between carbons on the hexagonal ring is1.40×10-10 m. It is different from ordinary single bonds (the bond length of C-C bond is1.54×10-10 m) and ordinary double bonds (the bond length of C=C bond is1.33×10-/kloc-0). From the fact that benzene can not react with potassium permanganate solution and bromine water and the experimental data of carbon-carbon bond length, it is fully explained that the carbon-carbon bond on benzene ring should be the only bond between single bond and double bond. Benzene can participate in three kinds of chemical reactions: one is the substitution reaction between other groups and hydrogen atoms on benzene ring; One is the addition reaction on the carbon-carbon double bond; One is the break of benzene ring. Uses are important raw materials for dyes, plastics, synthetic rubber, synthetic resin, synthetic fiber, synthetic drugs and pesticides, solvents for paints, rubber and glue, and can also be used as fuel. Physical and chemical hazards to health: high concentration of benzene has anesthetic effect on the central nervous system, causing acute poisoning; Long-term exposure to benzene is harmful to hematopoietic system and causes chronic poisoning. Acute poisoning: mild cases include headache, dizziness, nausea, vomiting, mild excitement, stumbling and other drunkenness; In severe cases, coma, convulsion and blood pressure drop occur, leading to respiratory and circulatory failure. Chronic poisoning: mainly manifested as neurasthenia syndrome; Hematopoietic system changes: leukopenia and thrombocytopenia, severe aplastic anemia; Leukemia can occur in a few cases after chronic poisoning (acute granulocytic is the most common). Skin lesions include degreasing, dryness, chapped skin and dermatitis. It can cause an increase in menstrual flow and a prolonged menstrual period. Environmental hazards: harmful to the environment and can pollute water bodies. Danger of explosion: This product is flammable and carcinogenic. Hazard characteristics: flammable, its vapor and air can form an explosive mixture, which is easy to burn and explode in case of open flame and high heat. Can react strongly with oxidant. It is easy to generate and accumulate static electricity, which is in danger of combustion and explosion. Its vapor is heavier than air, and it can spread to a considerable distance at a lower place, and it will catch fire when it meets a fire source. 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