Aromatic compounds are a kind of compounds with benzene ring structure.[5]They are stable in structure and difficult to decompose, which may cause serious pollution to the environment.In history, a class ofVegetable gumWitharomaticThe substances that smell are called aromatic compounds.Aromatic compounds generally mean that the molecule contains at least oneOff field keyOfCyclic compound, but modern aromatic compounds do not containbenzene ringExample of.All aromatic compounds are "aromatic".
Modern aromatics refer to hydrocarbon molecules containing at least one delocalized bondbenzene ring, with andOpen chain compoundorAlicyclic hydrocarbonA class of organic compounds with different unique properties (called aromaticity).asbenzene、naphthalene、anthracene, Philippines and itsderivative。Benzene is the simplest and most typical representative.They are prone to electrophilic substitution reaction and relatively stable to heat, mainly from oil andcoal tar。
benzene ring
Some compounds that do not contain benzene ring but also have aromatic properties similar to benzene are calledNon benzene aromatic compounds, such asGrass salt、AzuleneEtc.Organic compounds with benzene rings in their molecules are called aromatic compounds.It includesAromatic hydrocarbonAnd its derivatives, such asHalogenated aromatic hydrocarbon、Aromatic nitro compounds、Aromatic alcohol、Aromatic acid、steroidetc.[1]。
Originally, it refers to compounds with benzene ring in the molecule.In the middle of the 19th century, chemists found that there were quite a fewOrganic compoundIt has some special properties. In its molecular formula, the hydrogen atom andcarbon atomThe ratio is often less than 1, but theirchemical propertyIt's not like ordinaryUnsaturated compound。For example, they are not easy to get upAddition reactionAnd easy to get upSubstitution reactionMany of these compounds have aromatic smell, and some are extracted from spices, so they were called aromatic compounds at that time.Later, it was found that aromatic compounds were derivatives generated from the substitution of one or more hydrogen atoms of benzene molecules by other atoms or atomic groups.Some compounds can be regarded as connected by benzene through two or more carbon atomspolycyclicThey also belong to aromatic compounds, such as naphthalene and anthracene.Since the 1930s, the meaning of aromatic compounds has further developed.Some compounds do not contain benzene ring, but have some properties of aromatic compounds, such as:Phenone、FerroceneThese compounds are non benzene aromatic compounds.
Other compounds can beHull ruleTo determine whether it is aromatic.The specific expression is toconjugateFor the single ring, plane multi double bond matter with (4n+2) delocalizationπ electron(where n is an integer greater than or equal to zero) may have special aromatic stability.So like pyridineHeterocycleAll substances are aromatic.Their derivatives are also aromatic compounds.[1]
classification
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All hydrocarbons with aromatic benzene ring or heterocycle.It can be divided into two categories: ① benzene hydrocarbon or single benzene aromatic hydrocarbon, compounds with one benzene ring and their derivatives.Such as benzene, phenol, halogenated benzene, toluene, etc.; ②Polycyclic aromatic hydrocarbons (PAHs) are polycyclic hydrocarbons with common ring edges of benzene or heterocycles.Such as naphthalene, anthracene, perylene, benzopyrene, etc.For example, the polycyclic compounds formed by two or more benzene rings and heterocycles with common ring edges are called benzene fused heterocyclic compounds, such as indole, quinoline, fluorene, etc.The combustion emissions of 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 and bacteria in nature can also produce such compounds, such as eugenol, holly oil, etc.Many aromatic hydrocarbons are harmful substances in the environment, especially the pollution of polycyclic aromatic hydrocarbons (PAHs), which can cause mutagenicity and carcinogenicity, has attracted worldwide attention.[2]
(5) Having some special spectral characteristics, such as that of hydrogen outside the aromatic ringchemical shiftbe innuclear magnetic resonanceSpectrogramThe 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, many of which have aromatic odor.The main industrial sources are petroleum and coal tar.[1]
Substitution reaction
Is the majorityAromatic compoundIt is one of the important reactions in the synthesis of complex compounds from simple aromatic compounds through substitution reactions.In terms of mechanism, substitution reactions on aromatic nuclei include electrophilic, nucleophilic and free radical substitution, of which the most common isElectrophilic substitution, for example:Halogenation、nitrification、sulfonation、Alkylation, acylation, etc.Aromatic compounds have important applications in organic synthesis industry.
oxidation reaction
Any reaction that can increase oxygen or lose hydrogen in the molecule 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 reaction. These products are important intermediates and raw materials for organic synthesis, many of which have been widely used in medicine, pesticides, dyes, spices, various auxiliariesengineering plasticAnd functional polymers.Fused aromatic compounds are also prone to oxidation due to their electron rich structure.
Oxidation of benzene derivatives
P-hydroxybenzaldehydeyesSynthetic drugs, spices and pesticides.Its traditional preparation method is to oxidize p-cresol under homogeneous conditions, and its yield and selectivity are not ideal.It is reported in the literature that Co (OAc) loaded on activated carbon or molecular sievetwo· 4HtwoO as main catalyst, Cu (OAc)two·4HtwoO isCocatalyst, used for liquid-phase oxidation of p-cresol, with conversion of 99.4%, selectivity of 99.0% and yield of 98.4%.O-nitrobenzoic acidIt is an important raw material for making indigo and direct dyes. Its synthesis method is toO-nitrotolueneThere are many oxidation methods for oxidation, among which air catalytic oxidation is the most attractive method due to its low price and no catalyst post-treatment.3, 4-IIMethoxybenzoic acidIt has the effect of antifungal and preventing platelet aggregation. It is an important intermediate of synthetic drug Etoprazine, which can be made from vanillin (4-hydroxy-3-methoxybenzaldehyde) by methoxylation and oxidation. The oxidants reported in the literature areperacetic acid , phenyl trimethyl ammonium tribromide and sodium perborate, but the prices are higher.
Oxidation of naphthalene and its derivatives
Naphthalene is the simplestPolycyclic aromatic hydrocarbonNaphthalene and its homologues are high components in coal tar, petroleum cracking and reforming diesel oil.The oxidation products and oxygenated derivatives of naphthalene are widely used in the production of plasticizersalkyd resin , synthetic fibers, dyes, drugs, various chemical auxiliaries and monomers of functional polymer materials.Phthalic anhydride is the oxidation product of naphthalene, which is formed by esterification with monohydric alcoholDibutyl phthalate, dioctyl ester, dinonyl ester, nonyl cyclohexyl ester, etcPVC plasticPlasticizer;It is composed of phthalic anhydride andSaturated monohydric alcoholOr saturated diols and other condensates can be used to synthesize alkyd resins for paint production, and can also synthesize a variety of dyes, such as direct dyes, sulfur dyes, anthraquinone dyes, etc. The important ones are sun resistant turquoise blue, fluorescent yellow, Haichang yellow, and sulfurized light yellow.The oxidation of naphthalene to phthalic anhydride usually uses porous gas-solid catalyst VtwoOfive·KtwoSOfour/SiOtwo。The yield of phthalic anhydride can be increased by increasing the content of naphthalene in the feed mixture.Gas chromatography analysis showed that phthalic anhydride was formed 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 as antisympathic agents and nasal decongestants.with2-Naphthoic acid2-Propyl-2-naphthoate and its esters are highly effective insecticides.Using 2-naphthoic acid and its zinc salt as color developing agentThermal recording materialWith good anti plasticizer and solvent properties, the image formed is clear and has a long storage time;The 2-hydroxy-2-naphthylamide derivatives synthesized from 2-naphthoic acid derivatives and 2-hydroxy-2-naphthoic acid are excellentPhotosensitive material。Naphthylamine channelSodium nitriteDiazotize, replace it with naphthyl methylamine, keep it warm for 15 h with a mixture of glacial acetic acid, water and concentrated sulfuric acid in an oil bath at 115~120 ℃, dilute the product with equal volume of water, filter, wash it to neutral, and then use NatwoCOthreeDissolve the filter cake in aqueous solution, heat it and filter it while it is hot. Acidify it with excessive dilute sulfuric acid solution to obtain 2-naphthoic acid with a purity of 100%.
Oxidation of anthracene
The discovery of anthraquinone is an important milestone in the history of dye chemical industry.Anthraquinone dyes are the most numerous and widely used dyes, includingVat dye、reactive dye , direct dyesAcid dyeandDisperse dyeEtc.Anthraquinone is mainly produced by oxidation of anthracene.There are many patent documents about gas-solid catalytic oxidation of anthracene to anthraquinonetwoOfiveAs the main active component, the temperature is generally about 400 ℃.It is reported that MnOtwoIt can promote the oxidation of anthraquinone intermediate. If mild oxidation is required, granular, powdery or electrolytic MnO can be selectedtwoAs catalyst.In the production of anthraquinone from anthraceneSupported catalystVtwoOfiveFetwoOthreeThe reaction selectivity can be improved by changing the acid center on the catalyst surface and doping KtwoSOfourAnd CaSOfourThe selectivity of anthraquinone was increased from 57% to 89% and 97%, respectively.In AcOH and ActwoO, in the presence of ammonium vanadate and rare earth nitratetwoAnthracene oxide, anthraquinone yield 77.1%
In addition to anthraquinone, it can also be prepared from anthracenePyromellitic acid, it issynthetic resinImportant raw materials.Anthracene, RuClthree, NaClO and NaOH mixed in acetonitrile and reacted at 30 ℃ for 16 h, the yield of pyromellitic acid reached 43%.Recently, the oxidation of anthracene derivatives has also been studied.
Phenanthrene oxidation
The 9,10-phenanthraquinone obtained from phenanthrene oxide is often used as a pesticide to prevent grain smut and cotton seedling disease, as well as as a raw material for manufacturing benzophenone, a dye intermediate, and a pulp preservative.The product of deep phenanthrene oxide -diphenic acid yespolyester resin, alkyd resin andPlastic plasticizerRaw materials.In CHtwoCltwoIn the medium, phenanthrene can be easily oxidized to 9,10-diphenyl quinone with quinoline fluochromate. During the oxidation, there is an oxygen transfer.Yatabe is waiting for a small amount of ButhreeIn the presence of SnCl and dioxane aqueous solution, NaBrOtwoPhenanthrene oxide can be reacted at room temperature for 24 h to obtain phenanthraquinone in high yield.Phenanthrene undergoes gas-phase oxidation reaction in the presence of NOx, and the reaction starts to produceOH radicalAnd then initiate oxidation, and the products include fluorenone, 2,2 '- dicarbonylbiphenyl, 1,4 and 2,10 phenanthraquinone, 9,10 phenanthraquinone, dibenzopyranone and phenanthrone.Phenanthrene reacts in the presence of selenium dihydroxyphenylbenzenesulfonate, mainly producing phenanthraquinone in boiling dioxane water system, and 9 methoxyphenylene in methanol.In RuOfourIn the presence of NaClO and quaternary ammonium salt, the phase transfer catalytic oxidation of phenanthrene for 3~4 h can produce 2,2-biphenyltricarboxylic acid, with the yield of more than 85% and the purity of the product of more than 99%.Sarma et alQuinoline dichromatePhenanthrene oxide, from the analysis of experimental data, the rate determination step involves the H transfer process.Trapido et althreeReaction of phenanthrene oxide.Murray et althree)two= CC(CHthree)twoThe presence of phenanthrene and OthreeThe product is phenanthrene 9,10 dioxide.
Oxidation of acenaphthene
The 1,8-naphthalene dicarboxylic anhydride obtained from the oxidation of acenaphthene is the main raw material for the synthesis of polyester resin, alkyd resin and BG gray dye.After dehydrogenation of acenaphthene, acenaphthene is formed. The reaction can be carried out at room temperature in the presence of NBS and under light conditions.Polyacenaphthene resin produced by polymerization of acenaphthene 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.Jiang Zhiqin found that under the sensitization of 9,10-dicyanoanthrene or 9-cyanoanthrene, acenaphthene produced completely different carbonyl containing products such as monoketone, diketone, acid anhydride and acid aldehyde in acetonitrile, of which the product of polyacenaphthene was 50%.The 1,4,5,8-naphthalentetetracarboxylic acid (1,4,5,8-NTCA) can be synthesized by the oxidation of acenaphthene with some groups introduced directionally into the 4,5 position of acenaphthene under mild conditions using highly active catalysts.1, 4, 5, 8-NTCA is an intermediate for the synthesis of advanced dyes such as Yindanshilin bright orange GR. The dyes synthesized from 1, 4, 5, 8-NTCA have bright colors, high fastness and good heat resistance;Advanced level can also be synthesized from 1, 4, 5, 8-NTCAPolyimide resinThe 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, etc;1, 4, 5, 8-NTCA is also an important raw material for producing high-performance fibers.
Oxidation of fluorene
Fluorenone, the oxidation product of fluorene, can be used as an anticancer agent, a sympathetic nerve inhibitor and a herbicide.Marlin mixed fluorene, carbon tetrachloride and tetrabutylammonium hydrate, stirred at 30 ℃ for 15 min to obtain fluorene dichloride in 9726% 。 Fluorenone can be obtained quantitatively from dichlorofluorene treated with sulfuric acid.At VtwoOfiveFetwoOthreeOxidation of fluorene and doping Cs in the presence oftwoSOfourIt can improve the selectivity of fluorenone.KMnO for Ando, etcfourIt was found that ultrasonic radiation could accelerate the reaction rate of fluorene.Baur formed fluorenone and fluorenol in dicyclohexyl, and the selectivity of fluorenone reached 985% 。Bartlett once reported that 9-methoxymethylene fluorene with electron rich groupcarbon tetrachlorideFree radical photooxidation can occur in.Jiang Zhiqin studied the photooxidation reaction of 9-benzylidene fluorene (BF), and found that the reaction of fluorenone formation in acetonitrile solution of photosensitizer 9,10-dicyanoanthrene was quite rapid, but it was very slow in carbon tetrachloride, which was contrary to Bartlett's report.[3]
Degradation pathway
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Monocyclic aromatic hydrocarbon
Benzene degradation
Figure 1
The research on benzene degradation 30 years ago has been very successful.There are two branch pathways for benzene degradation, as shown in a in Figure 1.The benzene ring is initially formed by the attack of benzene dioxygenaseCatechol, catechol further produces muconic acid semialdehyde or muconic acid through the action of meta or ortho dioxygenase.
Degradation of substituted benzene
The existence of substituent groups makes the degradation of benzene ring appear two possibilities: the benzene ring is degraded first or the side chain is degraded first.The general route of monoalkyl substituted benzene containing 2~7 carbon atoms is shown in b) in Figure 1.When C>7, the substituted hydrocarbon chain is first degraded by β, ω oxidation, and then the benzene ring is degraded.The oxidation of long alkyl side chains is enough to provide growth energy for microorganisms, so that microorganisms will not degrade benzene ring.
Degradation of biphenyl
The pathway of biodegradation of biphenyl is as shown in c in Figure 1. There are two pathways for the degradation of oxygenated biphenyl: 1, 2 position oxygenation and 3, 4 position oxygenation. The former is the most common. Biphenyl undergoes two-step dioxygenase action to form 2-hydroxy-6-keto-6-phenyl-2, 3-hexanedioic acid (HOPDA), which is further degraded to benzoic acid (BA).Biphenyls and low-grade substituted biphenyls can also be degraded by microorganisms, and the degradation products are uni and di-n compounds.
Polycyclic aromatic hydrocarbons
Polycyclic aromatic hydrocarbons (PAH) are compounds containing two or more fused aromatic rings produced by incomplete combustion of organic substances.The pathway of microbial degradation of Cai is shown in d in Figure 1.The degradation of other aromatic compounds is the same. In the first step, the dioxygenated bacteria attack the ring to form 1,2 - via the radical, and then break between the first and ninth carbon atoms.[4]
Oxygenase
Benzene ring compounds are difficult to decompose because of their benzene ring structure. To decompose them under normal temperature and pressure, it must rely on the participation of enzymes.Enzymes 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 cleaving oxygenase ¨ 3'Hj.Phenylcyclohydroxylation oxygenase adds two hydroxyl groups to the benzene ring by providing electrons through oxygen molecules and NADH or NADPH. For example, toluene is catalyzed by toluene dioxygenase to form cis with oxygen molecules
Toluene dihydrodiol.Benzene ring cleaving oxygenase is the epoxidation and ring opening of benzene by oxygen molecules. For example, catechol forms muconic acid or muconic acid semialdehyde under the action of oxygen molecules and enzymes.The earliest phenylcyclohydroxylation oxygenase was prepared by Gibson et alPseudomonas putidaAll the enzymes isolated from Fl belong to the complex enzyme system and are composed of 2 to 3 proteins, but there are considerable differences in the composition of subunits.Batie et al. divided it into three categories: ClassI, Class II and ClassUl.Clam is composed of two components, while ClasslI and ClassHI are composed of three components.Phenyl cyclocleaving oxygenase can be divided into two forms during ring opening reaction: one is cleavage within dihydroxy group, also known as ortho cleavage;The other is external cutting of dihydroxy group, also called meta cutting.[3]
