Basic introduction Chinese name: aromatic compound mbth: aromatic compound? Nickname: Aromatic compounds abbreviation: Aromatic classification: Benzene hydrocarbons and polycyclic aromatic hydrocarbons have properties: typical representatives of aromaticity: benzene, naphthalene, anthracene, phenanthrene and their derivatives brief introduction classification, properties, aromaticity, substitution reaction, oxidation reaction, degradation pathway, monocyclic aromatic hydrocarbons, polycyclic aromatic hydrocarbons, oxygenase, brief introduction Modern aromatic hydrocarbons refer to hydrocarbon molecules containing at least one barrier. Such as benzene, naphthalene, anthracene, phenanthrene and their derivatives. Benzene is the simplest and most typical representative. They are prone to electrophilic substitution and relatively stable to heat, mainly from petroleum and coal tar. Some compounds, which do not contain benzene rings in their molecules, have aromaticity similar to benzene, and are called non-benzene aromatic compounds, such as grass salt and azulene. Organic compounds containing benzene rings in their molecules are called aromatic compounds. Include aromatic hydrocarbons and their derivatives, such as halogenated aromatic hydrocarbons, aromatic nitro compounds, aromatic alcohols, aromatic acids, steroids, etc. Benzene ring refers to a compound containing benzene ring in its molecule. /kloc-in the middle of the 0/9th century, chemists found that quite a few organic compounds had some special properties. The ratio of hydrogen atom to carbon atom in its molecular formula is often less than 1, but its chemical properties are not like ordinary unsaturated compounds. For example, they are not easy to carry out addition reaction, but easy to carry out substitution reaction. Many of these compounds have aromatic smells, and some of them are extracted from spices, so they were called aromatic compounds at that time. Later, it was found that aromatic compounds were derivatives of benzene, in which one or more hydrogen atoms were replaced by other atoms or groups. Some compounds can be regarded as polycyclic systems in which benzene is linked by two or more carbon atoms. They also belong to aromatic compounds such as naphthalene and anthracene. After 1930s, the meaning of aromatic compounds has been further developed. Some compounds do not contain benzene rings, but have some properties of aromatic compounds, such as phenol ketone and ferrocene, which can be substituted. These compounds are non-benzene aromatic compounds. Other compounds can be judged whether they are aromatic according to Huck's rule. Specifically, molecules with (4n+2) delocalized π electrons (where n is an integer greater than or equal to zero) may have special aromatic stability for fully * * * conjugated, monocyclic and planar multi-double bond substances. Therefore, heterocyclic substances such as pyridine are aromatic. Their derivatives are also aromatic compounds. Use aromatic benzene rings or heterocyclic rings to classify all hydrocarbons. It can be divided into two categories: ① Benzene hydrocarbons or monophenylarenes, compounds with a benzene ring and their derivatives. Such as benzene, phenol, halogenated benzene, toluene, etc. ; (2) Polycyclic aromatic hydrocarbons (PAHs), polycyclic hydrocarbons containing benzene rings or heterocyclic rings. Such as naphthalene, anthracene,? , perylene, benzopyrene and so on. For example, polycyclic compounds formed by two or more benzene rings and heterocyclic rings and * * * are called benzene fused heterocyclic compounds, such as indole, quinoline and fluorene. The combustion emissions from coking, petrochemical, dyestuff, pharmaceutical, pesticide and coating industries and fossil fuels are the main man-made sources of aromatic hydrocarbons in the environment. Some plants and bacteria in nature can also produce such compounds, such as eugenol and wintergreen oil. Many aromatic hydrocarbons are harmful substances in the environment, especially the pollution of polycyclic aromatic hydrocarbons can cause mutation and carcinogenesis, which has attracted worldwide attention. Aromaticity (1) has a planar or nearly planar ring structure; (2) The bond length tends to be average; (3) High hydrocarbon ratio; (4) Aromatic rings of aromatic compounds are generally difficult to be added by oxidation, but electrophilic substitution is easy to occur; (5) It has some special spectral characteristics, such as the chemical shift of hydrogen outside the aromatic ring is in the low field of NMR spectrum, while the hydrogen inside 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 of them have aromatic odor. The main industrial sources are petroleum and coal tar. Substitution reaction is one of the important reactions of most aromatic compounds, and simple aromatic compounds can synthesize more complex compounds through substitution reaction. The substitution reactions on aromatic nucleus include electrophilic substitution, nucleophilic substitution and free radical substitution in mechanism, among which electrophilic substitution is the most common, such as halogenation, nitration, sulfonation, alkylation and acylation. Aromatic compounds have important applications in organic synthesis industry. Oxidation reaction Any reaction that can increase oxygen or lose hydrogen in molecules or make elements and ions lose electrons is collectively called oxidation reaction. Aromatic compounds can be converted into aldehydes, ketones, carboxylic acids, quinones, epoxides and peroxides by oxidation. These products are important intermediates and raw materials for organic synthesis, and many of them have been widely used in the production of medicines, pesticides, dyes, spices, various additives, engineering plastics and functional polymers. Because of its electron-rich structure, fused aromatic compounds are also prone to oxidation. Oxidation of benzene derivatives p-hydroxybenzaldehyde is an intermediate for the synthesis of drugs, spices and pesticides. The traditional preparation method is to oxidize p-cresol under homogeneous conditions, and the yield and selectivity are not ideal. According to the literature, Co (OAC) 2 4H2O supported on activated carbon or molecular sieve is used as the main catalyst for liquid phase oxidation of p-cresol, and Cu (OAC) 2 4H2O is used as the cocatalyst. The conversion rate was 99.4%, the selectivity was 99.0% and the yield was 98.4%. O-nitrobenzoic acid is an important raw material for preparing indigo and direct dyes. Its synthesis method is oxidation of o-nitrotoluene, and there are many oxidation methods, among which air catalytic oxidation is the most attractive method at present because of its low cost and no need of catalyst post-treatment. 3,4-dimethoxybenzoic acid has antifungal and antiplatelet aggregation effects, and is an important intermediate for the synthesis of etopril. It can be prepared from vanillin (4- hydroxy -3- methoxybenzaldehyde) by methoxylation and oxidation. The oxidants reported in literature include peracetic acid, phenyltrimethyl ammonium bromide and sodium perborate, but their prices are very high. Naphthalene and its derivatives are the simplest polycyclic aromatic hydrocarbons, and naphthalene and its homologues are the components with high content in coal tar, petroleum cracking and reforming diesel oil. Oxidation products and oxygen-containing derivatives of naphthalene are widely used in the production of plasticizers, alkyd resins, synthetic fibers, dyes, drugs, various chemical additives and monomers of functional polymer materials. Phthalic anhydride is the oxidation product of naphthalene, and dibutyl phthalate, dioctyl ester, dinonyl ester and nonyl cyclohexyl ester produced by esterification with monohydric alcohol are plasticizers of PVC plastics. Alkyd resin can be synthesized from the polycondensate of phthalic anhydride with unsaturated monohydric alcohol or saturated dihydric alcohol, which can be used to produce paints. A variety of dyes, such as direct dyes, sulfur dyes and anthraquinone dyes, can also be synthesized, among which the important ones are light fast turquoise blue, fluorescent yellow, haichang yellow and light yellow sulfide. Porous gas-solid catalyst V2O5 K2SO4/SiO _ 2 is often used to oxidize naphthalene to phthalic anhydride. Increasing the naphthalene content in the feed mixture can improve the yield of phthalic anhydride. Gas chromatographic analysis shows that phthalic anhydride is produced by two consecutive steps. Tetrahydroimidazole derivatives synthesized from 1, 2,3,4-tetrahydro-1- naphthoic acid or its methyl ester and 1, 2- ethylenediamine are commonly used anti-sympathetic drugs and nasal congestion drugs. 2- propyl-2- naphthoic acid ester prepared from 2-naphthoic acid and its analogues are highly effective insecticides. The thermosensitive recording material with 2- naphthoic acid and its zinc salt as chromogenic agent has good plasticizer and solvent resistance, and the formed image is clear and can be stored for a long time. 2- hydroxy-2- naphthylamide derivative synthesized from 2- naphthoic acid derivative and 2-hydroxy -2- naphthoic acid is an excellent photosensitive material. Naphthylamine was diazotized with sodium nitrite and replaced with naphthylmethylamine. The mixture of glacial acetic acid, water and concentrated sulfuric acid was kept in an oil bath at 1 15 ~ 120℃ for 15 h, then the product was diluted with equal volume of water, filtered and washed to neutrality, and then the filter cake was dissolved with Na 2 CO 3 aqueous solution, heated and filtered while it was hot. The discovery of anthracene oxidized by anthraquinone is an important milestone in the development history of dye chemical industry. Anthraquinone dyes are the most abundant and widely used dyes, including vat dyes, reactive dyes, direct dyes, acid dyes and disperse dyes. Anthraquinone is mainly prepared by oxidation of anthracene. There are many patent documents on the gas-solid catalytic oxidation of anthracene to anthraquinone. V 2 O 5 is the main active component, and the temperature is generally around 400℃. It is reported that MnO _ 2 can promote the oxidation of anthraquinone intermediates. If slight oxidation is needed, MnO _ 2 in particle, powder or electrolytic form can be used as catalyst. Doping sulfate in V 2 O 5 Fe 2 O 3, an unsupported catalyst for anthracene to anthraquinone, can change the acid center on the catalyst surface, thus improving the reaction selectivity. Doping K 2 SO 4 and CaSO 4 can increase the selectivity of anthraquinone from 57% to 89% and 97% respectively. In the presence of ammonium vanadate and rare earth nitrate, anthracene is oxidized by O 2, and the yield of anthraquinone is 77.65438 0%. In addition to anthraquinone, pyromellitic acid can also be made from anthracene, which is an important raw material for synthetic resin. Anthracene, RuCl _ 3, NaClO and NaOH were mixed in acetonitrile and reacted at 30℃ for 65438±06h. The yield of pyromellitic acid was 43%. Recently, oxidation of anthracene derivatives has also been studied. Oxidation of phenanthrene 9, 10- phenanthroquinone obtained by oxidation of phenanthrene is often used as a pesticide to control head smut of grain and cotton seedling diseases, and can also be used as a raw material for making benzophenone, dye intermediates and pulp preservatives. Biphenyldicarboxylic acid is the product of deep phenanthrene oxide and the raw material of polyester resin, alkyd resin and plastic plasticizer. In CH 2 Cl 2 medium, phenanthrene is easily oxidized by quinoline fluorochromate to 9, 10- phenanthraquinone, and oxygen is transferred during the oxidation. Yatabe et al. oxidized phenanthrene with NaBrO 2 in the presence of a small amount of Bu 3 SnCl and dioxane-aqueous solution, and reacted at room temperature for 24 h to obtain phenanthraquinone in high yield. Phenanthrene undergoes gas phase oxidation in the presence of nitrogen oxides, which initially produces OH radicals and then initiates oxidation. The products are fluorenone, 2,2'-dicarbonyl biphenyl, 1, 4 and 2, 10- phenanthrone, 9,9 10- phenanthrone, dibenzopyranone and phenanthrone. Phenanthrene reacts in the presence of selenium diphenylsulfonate, phenanthrene quinone is mainly produced in boiling dioxane water system, and 9 methoxyphenanthrene is produced in methanol. In the presence of RuO 4 NaClO and quaternary ammonium salt, phenanthrene was oxidized by phase transfer catalysis for 3 ~ 4 h, and 2,2-biphenyltricarboxylic acid was prepared with a yield of more than 85% and a purity of more than 99%. Sarma et al used quinoline dichromate to oxidize phenanthrene. From the analysis of experimental data, the rate determination step involves the H transfer process. Trapido et al. studied the oxidation of phenanthrene with O 3 in aqueous solution. Murray et al. studied the reaction of phenanthrene with O 3 in the presence of (CH 3) 2 = CC(CH 3) 2, and the product was phenanthrene 9, 10- dioxide. Oxidation of acenaphthene 1, 8- naphthalenedicarboxylic anhydride is the main raw material for synthesizing polyester resin, alkyd resin and BG gray dye. Acenaphthene is generated after acenaphthene dehydrogenation, which can be carried out at room temperature in the presence of NBS and under illumination. Polyaacenaphthene resin produced by acenaphthene polymerization can replace phenolic resin. Takeshita et al. sensitized acenaphthene with rose red RB to produce cis or trans 1, 2- diol and its monoether derivatives. Ginger found that under the sensitization of 9, 10- dicyanoanthracene or 9- cyanoanthracene, acenaphthene produced completely different carbonyl-containing products in acetonitrile, such as mono-ketone, diketone, anhydride and aldehyde, of which 50% were acenaphthene. Under mild conditions, a highly active catalyst was selected, and some groups were directionally introduced into the 4- and 5- positions of acenaphthene, and then 1, 4,5,8-naphthalene tetracarboxylic acid (1, 4,5,8-ntca) was synthesized by oxidation reaction. 1, 4,5,8-ntca is an intermediate for the synthesis of advanced dyes such as indanthrene brilliant orange gr. The dyes synthesized from 1, 4,5,8-ntca have bright colors, high fastness and good heat resistance. 1, 4,5,8-ntca can also synthesize advanced polyimide resin, which has high temperature and radiation resistance, excellent mechanical and electrical insulation properties and can be used as special materials for aerospace vehicles. 1, 4,5,8-ntca is also an important raw material for producing high-performance fibers. Fluorenone, the oxidation product of fluorene, can be used as anticancer agent and sympathetic nerve inhibitor, and can also be used as herbicide. Marin mixed fluorene, carbon tetrachloride and tetrabutylammonium hydrate, and stirred at 30℃ for 65438±05min to obtain dichlorofluorene with a yield of 97. 26%. Fluorenone can be obtained quantitatively from dichlorofluorene treated with sulfuric acid. Oxidizing fluorene in the presence of V 2 O 5 Fe 2 O 3 and doping Cs 2 SO 4 can improve the selectivity of fluorenone. Ando et al. oxidized fluorene with KMnO 4 and found that ultrasonic radiation could accelerate the reaction rate. Baur produced fluorenone and fluorenone alcohol in dicyclohexyl, and the selectivity of fluorenone reached 98. 5%.Bartlett has reported that 9 methoxymethylene fluorene-rich groups can undergo free radical photooxidation in carbon tetrachloride. Jiang studied the photooxidation reaction of 9- benzylidene fluorene (BF), and found that the reaction of generating fluorenone in acetonitrile solution of photosensitizer 9, 10- dicyanoanthracene proceeded quite fast, but it proceeded very slowly in carbon tetrachloride, which was contrary to Bartlett's report. The degradation of benzene, a monocyclic aromatic hydrocarbon, was successful 30 years ago. There are two branching paths for benzene degradation, which are shown in figure 1(a). The benzene ring was initially attacked by benzene dioxygenase to form catechol, which further formed muconic acid semialdehyde or muconic acid through the action of meta-or ortho-dioxygenase. Degradation of substituted benzene There are two possibilities for benzene ring degradation: benzene ring degradation first or side chain degradation first. Figure 1(b) is a general method to substitute benzene with 2-7 carbon atoms. At 7 o'clock c >, the substituted alkyl chain is oxidized and degraded by β, ω, and then the benzene ring is degraded. The long alkyl side chain is oxidized enough to provide growth energy for microorganisms, so that microorganisms will not degrade benzene rings. The biodegradation pathway of biphenyl is shown in figure 1(c). There are two ways to degrade oxidized biphenyl: 1, 2-position oxidation and 3,4-position oxidation. The former is the most, and biphenyl forms 2- trans -6- ketone -6- phenyl-2,3-hexadienoic acid (HOPDA) through two-step dioxygenase. Biphenyl and low-substituted biphenyl can also be degraded by microorganisms, and the degradation products are single and double warping compounds. Polycyclic aromatic hydrocarbons (PAHs) are compounds containing two or more fused aromatic rings produced by incomplete combustion of organic compounds. The microbial degradation pathway of Cai is shown in figure 1(d). Similar to the degradation of other aromatic compounds, in the first step, the offensive ring of dioxygen forms 1, 2- which passes through the substrate and then breaks between 1 and the ninth carbon atom. The benzene ring compound of oxygenase is difficult to decompose because of its benzene ring structure. If we want to decompose at normal temperature and pressure, we must rely on the participation of enzymes. Oxidases involved in the metabolism of benzene ring compounds can be divided into two categories: one is benzene ring hydroxylation oxygenase; The other is benzene ring cleavage oxygenase (3'HJ). Benzene ring hydroxylation oxygenase is to add two hydroxyl groups to benzene ring through oxygen molecules and electrons provided by NADH or NADPH. For example, toluene is catalyzed by toluene dioxygenase to form cis with oxygen molecules.
Toluene dihydrodiol benzene ring cracking oxygenase is an oxygen molecule that oxidizes benzene ring and opens the ring. For example, catechol forms muconic acid or muconic acid semialdehyde under the action of oxygen molecules and enzymes. The earliest benzene ring hydroxylation oxygenase was isolated from Fl in pseudomonas putida by Gibson et al. All enzymes belong to a complex enzyme system, which consists of 2 ~ 3 kinds of protein, but the subunit composition is quite different. Batie et al. divided it into three categories: classic, second class and ClassUl. Clam consists of two components, while ClasslI and ClassHI consist of three components. Benzene ring cracking oxygenase can be divided into two forms in ring opening reaction: one is cleavage on dihydroxy, which can also be called ortho-cleavage; The other is cutting other than dihydroxy, which can also be called meta-cutting.