The aromatic compound is a class of compounds with a benzene ring structure. They are structurally stable, difficult to decompose, and highly toxic, causing serious pollution to the environment and causing great harm to the human body.

Historically, a class of substances with aromatic odors obtained from vegetable gums has been called aromatic compounds.

An aromatic compound in high school generally refers to hydrocarbon molecules containing at least with a delocalized bond of the benzene ring, but the presence of aromatic compounds containing no modern benzene example. The aromatic compounds all have “aromaticity“.

Aromatic Compound Definition

Modern aromatic hydrocarbon refers to a molecule containing at least one bond away domain benzene ring and having an open-chain compound or alicyclic hydrocarbons different unique properties (referred aromaticity a class of compounds, aromaticity) of.

Such as benzene, naphthalene, anthracene, phenanthrene, and derivatives. Benzene is the simplest and most typical representative. They are prone to electrophilic substitution reactions and are relatively stable to heat, mainly from petroleum and coal tar.

Aromatic compound

Some molecules, although they do not contain a benzene ring, have a similar aromatic compound to benzene, and are called non-benzene aromatic compounds such as grass salt, barium, and the like.

An organic compound containing a benzene ring in a molecule is called an aromatic compound. It includes aromatic hydrocarbons and their derivatives, such as halogenated aromatic hydrocarbons, aromatic nitro compounds, aromatic alcohols, aromatic acids, steroids, etc.

Initially refers to a compound containing a benzene ring in its molecule. In the mid-19th century, chemists found that quite a few organic compounds have some special properties.

Their hydrogen atom to carbon atom ratio is often less than 1, but their chemical properties are not like ordinary unsaturated compounds.

For example, they are not susceptible to addition reactions and are susceptible to substitution reactions. Many of these compounds have aromatic odors, some of which are extracted from perfumes, and are therefore referred to as aromatic compounds.

It was later discovered that the aromatic compound is a derivative in which one or more hydrogen atoms in the benzene molecule are replaced by other atoms or groups of atoms.

Some compounds can be regarded as polycyclic systems in which benzene is linked by two or more carbon atoms, and they are also aromatic compounds such as naphthalene and anthracene. After the 1930s, the meaning of aromatic compounds has been further developed.

Some compounds do not contain a benzene ring but have certain properties of aromatic compounds, such as phenol ketone, ferrocene, etc., which are non-benzene aromatic compounds.

Other compounds can be judged according to the Heckel rule for aromaticity.

The specific expression is that for a fully conjugated, monocyclic, planar multi-double bond species, there are (4n+2) delocalized π electrons (where n is an integer greater than or equal to zero), which may have special aromatic stability. Sex.

Thus, heterocyclic materials such as pyridine are aromatic. Their derivatives are also aromatic compounds.

Classification

A general term for all hydrocarbons having an aromatic benzene ring or a heterocyclic ring. Can be divided into two categories: 1 benzene or monophenyl arene, a compound with a benzene ring and its derivatives.

Such as benzene, phenol, halogenated benzene, toluene, etc.; 2 polycyclic aromatic hydrocarbons (PAH), polycyclic hydrocarbons having a benzene ring or a heterocyclic ring shared by the ring. Such as naphthalene, anthracene, anthracene, anthracene, benzopyrene and the like.

For example, a polycyclic compound in which two or more benzene rings and a heterocyclic ring are formed by a shared ring edge is called a benzene fused heterocyclic compound such as anthracene, a quinoline, an anthracene or the like.

Combustion emissions from coking, petrochemical, dye, pharmaceutical, pesticide, paint and other industries and fossil fuels are the main anthropogenic sources of aromatic hydrocarbons in the environment.

Some plants, bacteria, etc. in nature can also produce such compounds, such as eugenol, wintergreen oil and the like.

Many aromatic hydrocarbons are harmful substances in the environment, especially the pollution of polycyclic aromatic hydrocarbons can cause mutagenicity and carcinogenicity, which has attracted worldwide attention.

Nature

Aroma

(1) Having a planar or nearly planar annular structure;

(2) The bond length tends to be averaged;

(3) Has a higher C/H ratio;

(4) The aromatic ring of the aromatic compound is generally difficult to oxidize and add, and is prone to electrophilic substitution;

(5) It has some special spectral characteristics, such as the chemical shift of hydrogen outside the aromatic ring is in the low field of the nuclear magnetic resonance spectrum, while the hydrogen in the ring is in the high field.

Most aromatic compounds contain one or more aromatic rings (or aromatic nuclei). Aromatic compounds are widely distributed in nature, and many have aromatic odors. The main industrial sources are petroleum and coal tar.

Substitution reaction

It is one of the important reactions of most aromatic compounds. By the substitution reaction, more complex compounds can be synthesized from simple aromatic compounds.

The substitution reaction on the aromatic nucleus includes three types of electrophilic, nucleophilic and free radical substitution, the most common of which are electrophilic substitutions such as halogenation, nitration, sulfonation, alkylation, acylation and the like.

Aromatic compounds have important applications in the organic synthesis industry.

Oxidation reaction

Any reaction that increases oxygen or loses hydrogen in a molecule or causes an element or ion to lose electrons is collectively referred to as an oxidation reaction.

The oxidation reaction can be used to convert aromatic compounds into aldehydes, ketones, carboxylic acids, hydrazines, epoxides, and peroxides.

Aromatic compound

These products are important intermediates and raw materials for organic synthesis, many of which have been widely used in medicines and pesticides. In the production of dyes, perfumes, various additives, engineering plastics, and functional polymers.

The fused ring aromatic compound is also prone to oxidation reaction due to its electron-rich structure.

Oxidation of benzene derivatives

Para hydroxy benzaldehyde is an intermediate in the synthesis of pharmaceuticals, perfumes, and pesticides. Its traditional method is to oxidize p-cresol under homogeneous conditions, and the yield and selectivity are not ideal.

It is reported in the literature that Co(OAc)2·4H2O supported on activated carbon or molecular sieve is the main catalyst and Cu(OAc)2·4H2O is used as a promoter for liquid phase oxidation of p-cresol with a conversion rate of 99.4. %, selectivity 99.0%, yield reached 98.4%. O-nitrobenzoic acid is an important raw material for the preparation of indigo and direct dyes.

Its synthesis method is to oxidize o-nitrotoluene. There are various oxidation methods. The air catalytic oxidation method is cheap and has no post-catalyst treatment problems.

Become the most attractive method at the moment. 3,4-dimethoxybenzoic acid has antifungal and anti-platelet aggregation effects and is an important intermediate for the synthesis of the drug based on the tropics, which can be treated with vanillin (4-hydroxy-3-methoxybenzaldehyde).

The raw materials are made by methoxylation and oxidation. The oxidants reported in the literature are peroxyacetic acid, phenyltrimethylammonium tribromide, and sodium perborate, but the prices are high.

Oxidation of naphthalene and its derivatives

Naphthalene is the simplest polycyclic aromatic hydrocarbon, and naphthalene and its homologues are components of coal tar and petroleum cracking and reforming diesel.

The oxidation products and oxygen-containing derivatives of naphthalene are widely used in the production of plasticizers, alkyd resins, synthetic fibers, dyes, pharmaceuticals, various chemical auxiliaries, and monomers of functional polymer materials.

Phthalic anhydride is an oxidation product of naphthalene. It is a plasticizer for polyvinyl chloride plastics, which is formed by esterification of monohydric alcohol with dibutyl phthalate, dioctyl ester, dinonyl ester, and nonylcyclohexyl ester.

Polycondensates such as unsaturated monohydric alcohols or saturated diols can be synthesized into alkyd resins for the production of paints, etc., and can also synthesize various dyes, such as direct dyes, sulfur dyes, and anthraquinone dyes, fluorescent yellow, Haichang yellow and sulphurized yellow.

From the oxidation of naphthalene to phthalic anhydride, a porous gas-solid phase catalyst V2O5·K2SO4/SiO2 is mostly used. Increasing the content of naphthalene in the feed mixture can increase the yield of phthalic anhydride. Gas chromatography analysis showed that phthalic anhydride was formed by two consecutive steps.

A tetrahydroimidazole derivative synthesized from 1,2,3,4-tetrahydro-1-naphthoic acid or its methyl ester with 1,2-ethanediamine is a commonly used antisympathetic agent and a nasal congestion-reducing drug. 2-propyl-2-naphthoate and its esters produced from 2-naphthoic acid are highly effective insecticides.

The thermosensitive recording material using 2-naphthoic acid and its zinc salt as a color developing agent has good anti-plasticizer and solvent properties, and the formed image is clear and has a long storage time, a derivative of 2-naphthoic acid, 2 The 2-hydroxy-2-naphthocarboxamide derivative synthesized from -hydroxy-2-naphthoic acid is an excellent photosensitive material. Aromatic Compound

The naphthylamine is diazotized by sodium nitrite, replaced with naphthylamine, and incubated with a mixture of glacial acetic acid, water and concentrated sulfuric acid in an oil bath at 115-120 ° C for 15 h, then diluted with an equal volume of water, suction filtration, After washing to neutrality, the cake was dissolved in an aqueous solution of Na2CO3, heated and filtered while hot, and acidified with an excess of dilute sulfuric acid solution to obtain 2-naphthoic acid having a purity of 100%.

Oxidation of niobium

The discovery of cockroaches is an important milestone in the history of the development of the dye chemical industry. Anthraquinone dyes are the most widely used and widely used dyes, including vat dyes, reactive dyes, direct dyes, acid dyes and disperse dyes.

Niobium is mainly produced by niobium oxidation. There are many patent documents related to gas-solid phase catalytic oxidation of lanthanum, and V2O5 is the main active component, and the temperature is generally around 400 °C.

It has been reported that MnO2 can promote the oxidation of the ruthenium intermediate. If mild oxidation is required, MnO2 produced by granulation, powder or electrolysis can be used as a catalyst.

Doping the sulfate in the unsupported catalyst V2O5Fe2O3 made of lanthanum, changing the acid center of the catalyst surface, can improve the reaction selectivity, and doping K2SO4 and CaSO 4 can make Anthracene.

The selectivity of strontium increased from 57% to 89% and 97%, respectively. In the presence of AcOH and Ac 2 O, ammonium vanadate and rare earth nitrate, ruthenium O 2 is used, and the yield of ruthenium is 77.1%. Aromatic Compound

In addition to hydrazine, pyromellitic acid is also produced from hydrazine, which is an important raw material for synthetic resins. The ruthenium, RuCl3, NaClO, and NaOH were mixed in acetonitrile and reacted at 30 ° C for 16 h. The yield of pyromellitic acid was up to 43%. Recently, some studies have been conducted on the oxidation of anthraquinone derivatives.

Anodic oxidation

9 10-phenanthrenequinone obtained by fluorinated phenanthrene is often used as a pesticide to prevent grain smut and cotton seedling disease, and also as a raw material for the manufacture of dye intermediate benzopyrone and pulp preservative.

Aromatic compound

The product of deep oxidation of phenanthrene – phthalic acid is the raw material of polyester resin, alkyd resin, and plastic plasticizer. In CH 2 Cl 2 medium, phenanthroline can be easily oxidized to 9,10-diphenanthrene with a fluorochromic acid, and aerobic transfer during oxidation.

In the presence of a small amount of Bu3SnCl and a dioxane-water solution, Yatabe et al. oxidized phenanthrene with NaBrO2 and reacted at room temperature for 24 h to obtain phenanthrenequinone in high yield.

The phenanthrene undergoes a gas phase oxidation reaction in the presence of NOx. The reaction begins to produce OH radicals, which are then oxidized. The products are anthrone, 2,2′ -diformylbiphenyl, 1,4 and 2,10-phenanthrenequinone, 9 , 10-phenanthrene, dibenzopyrone and phenanthone.

The phenanthrene reacts in the presence of selenium dihydroxy phenyl benzenesulfonate, and phenanthrene is mainly formed in the boiling dioxane-water system, and 9 methoxy phenanthrene is formed in methanol. Aromatic Compound

In the presence of RuO 4 NaClO and quaternary ammonium salt, phase transfer catalytic oxidation of phenanthrene for 3 ~ 4 h, can produce 2,2-biphenyl tricarboxylic acid, the yield is greater than 85%, the product purity is greater than 99%.

Sarma et al. used quinolinate dichromate to oxidize phenanthrene. From the experimental data analysis, the rate-determining step involved the H transfer process.

Trapido et al. studied the reaction of phenanthrene oxide with O3 in an aqueous solution. Murray et al. studied the reaction of phenanthrene with O3 in the presence of (CH32 = CC(CH 3 ) 2 and the product was phenanthrene 9,10-dioxide.

Oxidation of niobium

The 1,8-naphthalic anhydride obtained by cerium oxide is a main raw material for synthesizing a polyester resin, an alkyd resin, and a BG gray dye.

The deuterium is dehydrogenated to form a terpene, which can be carried out at room temperature in the presence of NBS and under the light.

The polydecene resin produced by polymerization of terpene can replace the phenolic resin. Takeshita et al. sensitize terpene with Rose Bengal RB to form cis or trans 1,2-diol and its monoether derivatives.

Jiang Zhiqin found that under the sensitization of 9,10-dicyanoguanidine or 9-cyanide, terpene produces completely different ketone-containing products such as monoketones, diketones, acid anhydrides and acid aldehydes in acetonitrile, of which polydecene The product is 50%.

Highly active catalysts are used to introduce certain groups in the 4th and 5th positions of hydrazine under mild conditions, and 1,4,5,8-naphthalenetetracarboxylic acid can be synthesized by oxidation reaction (1,4,5,8). -NTCA). 1,4,5,8-NTCA is an intermediate for the synthesis of advanced dyes such as indanthrene bright orange GR. Aromatic Compound

The dyes synthesized from 1,4,5,8-NTCA have bright color, high fastness, and good heat resistance. Advanced polyimide resin can also be synthesized from 1,4,5,8-NTCA.

The resin is resistant to high temperature and radiation and has excellent mechanical and electrical insulation properties. It can be used as a special material for aerospace vehicles. 1,4,5,8-NTCA is also an important raw material for the production of high-performance fibers.

Oxidation of niobium

An anticancer agent and a sympathetic inhibitor can be produced from the oxime oxime ketone, and can also be used as an herbicide. Marlin is mixed with hydrazine, carbon tetrachloride and tetrabutylammonium hydrate, and stirred at 30 ° C for 15 min to give dichloropurine in a yield of 97.26%.

The obtained chloranil is treated with sulfuric acid to quantitatively obtain an anthrone. The ruthenium is oxidized in the presence of V2O5Fe2O3, and the doping of Cs2SO4 can increase the selectivity of the fluorenone.

Ando et al. used KMnO4 ruthenium oxide and found that the use of ultrasonic radiation can speed up the reaction. 5%。 The Baur in the dicyclohexyl group to form anthrone and sterol, wherein the selectivity of the fluorenone is 98.5%. Aromatic Compound

Bartlett has reported that 9-methoxymethylene fluorene with electron-rich groups can undergo free radical photooxidation in carbon tetrachloride.

Jiang Zhiqin studied the photooxidation of 9-benzylidene hydrazine (BF) and found that the reaction to form anthrone in the sensitizer 9,10-dicyanoguanidine in acetonitrile was carried out quite rapidly, but in carbon tetrachloride. It’s very slow, contrary to Bartlett’s report.

Degradation pathway

Monocyclic aromatic hydrocarbon

Degradation of benzene

The degradation of benzene has been very successful in research 30 years ago. There are two branch pathways for benzene degradation, as shown in Figure 1(a). The benzene ring is initially attacked by phenyl dioxygenase to form catechol, which further produces muconic acid semialdehyde or muconic acid by the action of a meta or ortho dioxygenase.

Degradation of substituted benzene

The presence of a substituent group causes two possibilities for degradation of the benzene ring: degradation of the benzene ring or degradation of the side chain first.

The general route for the substitution of benzene with a monohydrocarbyl group of 2 to 7 carbon atoms is shown in Figure 1(b). When C >7, the hydrocarbyl chain is first degraded by β,ω oxidation degradation, and finally the benzene ring is degraded.

The long hydrocarbyl side chain is oxidized enough to provide the microorganism with the energy to grow so that the microorganism does not degrade the benzene ring.

Biphenyl degradation

The biodegradable biphenyl pathway is shown in Figure 1(c). There are two pathways for the degradation of oxygenated biphenyl: 1, 2 oxygen and 3, 4 oxygen. The former is mostly, and biphenyl undergoes two-step dioxygenase. After formation of 2-bromo-6-keto-6-phenyl-2,3-hexadienoic acid (HOPDA), it is further degraded to benzoic acid (BA). Biphenyl and low-substituted biphenyls can also undergo microbial degradation, and the products of degradation are mono- and di-based compounds.

Polycyclic aromatic hydrocarbons

Polycyclic Aromatic Hydrocarbons (PAH) are a class of compounds containing two or more fused aromatic rings produced by incomplete combustion of organic matter. The pathway for microbial degradation of Cai is shown in Figure 1(d). In the same manner as the degradation of other aromatic compounds, in the first step, the double-oxygenase attacking ring forms 1,2 – via keel, followed by cleavage between the first and ninth carbon atoms.

Oxygenase

A benzene ring compound is difficult to decompose because of its benzene ring structure. If it is to be decomposed under normal temperature and pressure, it must rely on the participation of the enzyme.

Oxidase involved in the metabolism of benzene ring compounds can be divided into two categories: one is benzene ring hydroxylated oxygenase; the other is benzene ring cutting oxygenase ̈ 3’Hj.

The benzene ring hydroxylated oxygenase is provided by an oxygen molecule and NADH or NADPH to supply electrons to the benzene ring by adding two hydroxyl groups, such as toluene, which is catalyzed by toluene dioxygenase to form a cis-tolyl dihydrogendiol with oxygen molecules. Aromatic Compound

The benzene ring-cutting oxygenase is obtained by oxidizing a benzene ring by an oxygen molecule and performing ring-opening.

For example, catechol forms a muconic acid or a muconic acid semialdehyde under the action of an oxygen molecule and an enzyme.

The earliest benzene-ring hydroxylated oxygenase was isolated from P. pseudomonas Fl by Gibson et al.

All enzymes belonged to the complex enzyme system and consisted of 2 to 3 proteins but in the composition of the subunits. There are quite a few differences.

Batie et al. divided it into three categories: Class I, ClassII, and ClassUl. Clam is composed of two components, while ClasslI and ClassHI are composed of three components.

The benzene ring-cutting oxygenase can be divided into two forms in the ring-opening reaction: one is to cut in the dihydrooxy group, which can also be called ortho-cut; the other is to cut outside the dihydrogen group. It can also be called a bit cut.