Si Nuo. 7 1-43-2
RTECS number CY 1400000
Smile C 1=CC=CC=C 1
Chemical formula C6H6
The molar mass is 78.11g mol-1.
The density is 0.8786 g/ml.
Melting point: 278.65 K (5.5℃)
Boiling point: 353.25 K (80. 1℃)
The solubility in water is 0.18g/100 ml of water.
Standard molar entropy so 298173.26 j/mol k
Standard molar heat capacity CPO135.69 j/mol k (298.438+05k)
Flash point-10. 1 1℃ (closed cup)
The spontaneous combustion temperature is 562.22℃. Edit this paragraph | Back to the top, it is found that benzene was first synthesized when gas was used as lighting gas in the early18th century.
1803 ~1819g.t. accum produced many products, some of which contained a small amount of benzene by modern analytical methods.
1825, michael faraday 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 experimental formula (C6H6) of six carbons and six hydrogen atoms in benzene molecule.
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.
Kekule's double bond swing model 1865, Friedrich Kekule proposed the structure of alternating single and double bonds of benzene ring and infinite yoke, which is now called Kekule type. His explanation for this structure is 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. It is also said that drawing the molecular structure of benzene into a hexagonal ring structure was first proposed by the French chemist Auguste Lauren in his book Chemical Methods in 1854. But for some reason, Kekule didn't mention Lauren's achievements in his paper.
In addition, james dewar discovered a benzene analog; Named "Dewar benzene", it has been proved that it can be obtained from benzene by light.
1865, benzene became an industrial product. 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. Edit this paragraph | Back to the top material structure The delocalized large π -bond benzene in benzene molecules has a benzene ring structure, which makes it have special aromaticity. Benzene ring is the simplest aromatic ring, which consists of six carbon atoms, and each carbon atom has a group behind it. All six groups of benzene are hydrogen atoms.
Cycloolefins with a carbon number of 4n+2(n is a positive integer, that is, benzene is n= 1) and a structure with alternating single and double bonds are called annulenes, and benzene is a kind of annulenes. (See "4n+2 rule")
Benzene is a planar molecule with 12 atoms on the same plane, and six carbons and six hydrogens are equal. The bond length of C-H is 1.08α, and the bond length of C-C is 1.40α, which is between single bond and double bond. All bond angles in the molecule are 120, and all carbon atoms are sp2 hybridized. Each carbon atom still has a P orbit perpendicular to the molecular plane, and each benzene molecule has an electron on the σ bond orbit. Six orbits overlap to form a delocalized large π bond. According to linus pauling's vibrational hybridization theory, the existence of vibrational hybridization in benzene ring is the reason why benzene ring is very stable, which also directly leads to its aromaticity.
According to the molecular orbital theory, six p orbitals of benzene interact to form six π molecular orbitals, among which ψ 1, ψ2 and ψ3 are low-energy bond orbitals, and ψ4, ψ5 and ψ6 are high-energy anti-bond orbitals. ψ2, ψ3, ψ4 and ψ5 are two pairs of degenerate orbits. The electron cloud distribution of benzene in the ground state is the result of the superposition of three bonding orbitals, so the electron cloud is evenly distributed above and below the benzene ring and on the ring atoms, forming a closed electron cloud. It is the source of ring current generated by benzene molecules in magnetic field. Edit this paragraph | Topping physical properties The boiling point of benzene is 80. 1℃, and the melting point is 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.
According to Antoine equation, the saturated vapor pressure between 10- 1500mmHg can be calculated.
lgP = A - P/(C + t)
Parameters: A = 6.9 12 10, B = 12 14.645, C = 22 1.205.
Where the unit of p is mmHg and the unit of t is℃. Edit this paragraph | Back to the top chemical benzene participates in three kinds of chemical reactions: one is the substitution reaction between other groups on the benzene ring and hydrogen atoms; One is the addition reaction on the carbon-carbon double bond; One is the break of benzene ring.
displacement reaction
See "substitution reaction" and "electrophilic aromatic substitution reaction" for details.
Under certain conditions, the hydrogen atom on the benzene ring can be substituted by halogen, nitro, sulfonic acid group, hydrocarbon group and so on. , and can generate the corresponding derivative. Because of different substituents, the position and number of hydrogen atoms are different, and isomers with different numbers and structures can be generated.
The electron cloud density of benzene ring is relatively high, so the substitution reaction on benzene ring is mostly electrophilic substitution. Electrophilic substitution is a typical reaction of aromatic rings. When benzene substituents are electrophilic, the position of the second substituent is related to the original substituent.
halogenation
The general formula of benzene halogenation reaction can be written as:
PhH+X2——→PhX+HX
During the reaction, halogen molecules are heterozygous under the action of benzene and catalyst, X+ attacks benzene ring, and X- combines with catalyst.
Taking bromine as an example, iron powder needs to be added in the reaction, and iron is converted into ferric tribromide under the action of bromine.
Catalytic process:
FeBr3+Br-——→FeBr4-
PhH+Br+FeBr4-——→PhBr+FeBr3+HBr
In industry, the substitution of chlorine and bromine in halogenated benzene is the most important.
nitrify
Benzene and nitric acid can produce nitrobenzene with concentrated sulfuric acid as catalyst.
PhH+HO-NO2——→PhNO2+H2O
Nitrification is a strong exothermic reaction, which is easy to produce substitutes, but the further reaction speed is slow.
Sulfonation reaction
Benzene can be sulfonated into benzene sulfonic acid with concentrated sulfuric acid or fuming sulfuric acid at higher temperature.
PhH+HO-SO3H——→PhSO3H+H2O
After sulfonic acid group is introduced into benzene ring, the reaction ability decreases and it is not easy to be further sulfonated. The introduction of the second and third sulfonic acid groups requires a higher temperature. This shows that nitro and sulfonic groups are passivation groups, that is, groups that hinder electrophilic substitution again.
Fred-Crawford reaction
Under the catalysis of AlCl3, benzene can also react with alcohols, olefins and halogenated hydrocarbons, and the hydrogen atoms on the benzene ring are replaced by alkyl groups to produce alkylbenzene. This reaction is called alkylation, also known as Fred-Crawford alkylation. For example, ethylbenzene is produced by alkylation of ethylene.
PhH+CH2=CH2—AlCl3→Ph-CH2CH3
During the reaction, the R group may be rearranged: for example, 1- chloropropane reacts with benzene to produce cumene, because free radicals always tend to a stable configuration.
Under the catalysis of strong Lewis acid, benzene reacts with acyl chloride or carboxylic anhydride, and the hydrogen atom on the benzene ring is replaced by acyl group to produce acyl benzene. The reaction conditions are similar to alkylation.
Addition reaction (addition reaction)
See "addition reaction"
Although the benzene ring is very stable, the addition reaction of double bonds can also occur under certain conditions. Usually by catalytic hydrogenation, using nickel as catalyst, benzene can produce cyclohexane.
C6H6+3H2——→C6H 12
In addition, the reaction of producing hexachlorocyclohexane (HCH) from benzene can be obtained by the addition of benzene and chlorine under ultraviolet irradiation.
Oxidation reaction (redox)
burn
Like other hydrocarbons, benzene can burn. When oxygen is sufficient, the products are carbon dioxide and water. But when burning in the air, the flame is bright and there is thick black smoke. This is due to the large mass fraction of carbon in benzene.
2c6h 6+ 15o 2——→ 12co 2+6H2O
ozonization
Benzene can also be oxidized by ozone under certain conditions, and the product is glyoxal. This reaction can be regarded as the ozonation reaction of cyclic polyene produced after benzene delocalization.
Under normal circumstances, benzene cannot be oxidized by strong oxidants. However, in the presence of a catalyst such as molybdenum oxide, benzene can be selectively oxidized to maleic anhydride by reacting with oxygen in the air. This is one of the few reactions that can destroy the six-membered carbocyclic system of benzene. (Maleic anhydride is a five-membered heterocyclic ring. )
This is a strongly exothermic reaction.
Other reactions
Using iron, copper and nickel as catalysts, benzene can be condensed to biphenyl at high temperature. Chlorotoluene can be produced from formaldehyde and hypochlorous acid in the presence of zinc chloride. And alkyl metalates such as sodium ethyl can react to form phenyl metalates. Phenyl Grignard reagent can be prepared by reacting with magnesium in tetrahydrofuran, chlorobenzene or bromobenzene. Edit this paragraph | Back to the top preparation method