Naphthalene oxidation reaction. IV.4
The simplest of the condensed benzoic hydrocarbons is naphthalene:
Positions 1,4,5 and 8 are designated "α", positions 2, 3,6,7 are designated "β".
Ways to get.
The bulk of naphthalene is obtained from coal tar.
In laboratory conditions, naphthalene can be obtained by passing benzene and acetylene vapors over charcoal:
Dehydrocyclization over platinum of benzene homologues with a side chain of four or more carbon atoms:
By the reaction of the diene synthesis of 1,3-butadiene with P-benzoquinone:
Naphthalene is a crystalline substance with T pl. 80 0 C, characterized by high volatility.
Naphthalene enters into electrophilic substitution reactions more easily than benzene. In this case, the first substituent almost always becomes in the α-position:
Entry of an electrophilic agent into the β-position is less common. As a rule, this occurs in specific conditions. In particular, the sulfonation of naphthalene at 60 0 C proceeds as a kinetically controlled process with the predominant formation of 1-naphthalenesulfonic acid. Sulfonation of naphthalene at 160 0 C proceeds as a thermodynamically controlled process and leads to the formation of 2-naphthalenesulfonic acid:
When a second substituent is introduced into the naphthalene molecule, the orientation is determined by the nature of the substituent already present in it. Electron donor substituents located in the naphthalene molecule direct the attack to the same ring in the 2nd and 4th positions:
The electron-withdrawing substituents located in the naphthalene molecule direct the attack to another ring in the 5th and 8th positions:
Oxidation
Oxidation of naphthalene with atmospheric oxygen using vanadium pentoxide as a catalyst leads to the formation of phthalic anhydride:
Recovery
Naphthalene can be reduced by the action of various reducing agents with the addition of 1, 2 or 5 moles of hydrogen:
2.2. Anthracene, phenanthrene
By building up another ring from naphthalene, two isomeric hydrocarbons can be obtained - anthracene and phenanthrene:
Positions 1, 4, 5 and 8 are designated "α", positions 2, 3, 6 and 7 are designated "β", positions 9 and 10 are designated "γ" or "meso" - the middle position.
Ways to get.
The bulk of anthracene is obtained from coal tar.
Under laboratory conditions, anthracene is obtained by the Friedel-Crafts reaction from benzene or with tetrabromoethane:
or by reaction with phthalic anhydride:
As a result of the reaction, anthraquinone is obtained, which is easily reduced to anthracene. For example, sodium borohydride:
The Fittig reaction is also used, according to which the anthracene molecule is obtained from two molecules ortho- bromobenzyl bromide:
Properties:
Anthracene is a crystalline substance with T pl. 213 0 C. All three benzene rings of anthracene lie in the same plane.
Anthracene easily adds hydrogen, bromine and maleic anhydride to positions 9 and 10:
The bromine addition product easily loses hydrogen bromide to form 9-bromoanthracene.
Under the action of oxidizing agents, anthracene is easily oxidized to anthraquinone:
Phenantrene, as well as anthracene, is a constituent of coal tar.
Just like anthracene, phenanthrene adds hydrogen and bromine to the 9,10 positions:
Under the action of oxidizing agents, phenanthrene is easily oxidized to phenanthrenquinone, which is further oxidized to 2,2`-bifenic acid:
11 > .. >> Next
Oxidation
3I
Benindustri for the production of ?-naphthol, phthalic anhydride and other intermediates, plasticizers, tanning agents, antioxidants, wetting agents and an emulsifier for Buna rubber; 4073 g purchased by other companies; 15,600 tons for the production of gas soot and 2,400 g for lamp soot; 4600 t for insecticides, 2300 t for antioxidants, 1700 t for lubricants and 400 g for other uses (pesticides, insulation materials, diesel fuel)""
Oxidation
Naphthalene is oxidized and reduced much more clearly than benzene. Both of these reactions are of great industrial importance, especially the oxidation of naphthalene with splitting of one ring and the formation of phthalic anhydride.
Oxidation without splitting the ring. Naphthalene can be oxidized directly to a-naphthol and 1,4-naphthoquinone, which, however, are obtained in low yields.
a-Naphthol can be obtained as its acetyl derivative (2.9 g from 20 a of naphthalene) by heating the hydrocarbon with lead tetraacetate in glacial acetic acid68. When naphthalene is oxidized, β-naphthol is usually not formed. However, traces of it were found after exposure of the hydrocarbon to sunlight in the presence of nitrobenzene in a nitrogen atmosphere for six months59. In addition, it has been obtained in very low yield by the oxidation of naphthalene under high oxygen pressure over iron oxide (as a catalyst) in the presence of hydrogen fluoride60.
1,4-Naphthoquinone is usually present in the oxidation products of naphthalene; as a rule, it is mixed with other products. In the production of phthalic anhydride, 1,4-naphtho-quinone is obtained as an impurity, especially at low temperatures and insufficient air excess. So, if naphthalene vapor is passed over the catalyst (vanadium pentoxide + potassium sulfate) at 430 0C and the ratio of air:naphthalene=40:1, then the yield of 1,4-naphthoquinone at a contact time of 0.4 tech62 is 15%. The yield of 1,4-naphthoquinone reaches 25% when passing naphthalene vapor over vanadium pentoxide (10%) on pumice at
* According to the statistical collection NIITEKHIM (I960), in Germany in 1957, naphthalene was produced: raw 110,000 tons, hot pressing - 87,700 tons, pure - 11,500 tons - Note. ed.
32
Chapter /¦ Naphthalene
418 0C (external temperature) "with a contact time of 0.13 sec and 6.5 times the amount of air against that required for complete oxidation of naphthalene63. 1,4-Naphthoquinone can be obtained by oxidation of naphthalene with chromic anhydride in heated glacial acetic acid (yield crude product 43%)61, hydrogen peroxide in acetic acid (yield 20%)64 or electrolytically using 1% sulfuric acid as an electrolyte and a mixture of naphthalene and carbon in a platinum grid as an anode (yield 30.4%) 65. For the I. G. Farben industry method using dichromate and acid, see p. 451. A special method for the oxidation of β-methylnaphthalene to 2-methyl-1,4-naphthoquinone (vitamin K3, pp. 467-468)66 has been patented. , according to which i?-methylnaphthalene dissolved in carbon tetrachloride is oxidized with an aqueous solution of KjCr2O-.
Oxidation with splitting of the ring. With deeper oxidation of naphthalene, one ring breaks. The remaining benzene ring is comparatively resistant to oxidizing agents, so that phthalic anhydride or phthalic acid can be obtained in high yield under appropriate conditions. The production of these compounds from naphthalene is of great technical importance and is discussed in detail below. Compounds corresponding to intermediate oxidation steps have also been obtained. In o-carboxyallocinic acid
all ten carbon atoms of the naphthalene core are retained. It was obtained as follows67:
Naphthalene (10 g) is mixed with peracetic acid (89 g of 26% acid). As the reaction proceeds, the hydrocarbon goes into solution. After 17 days, o-carboxylic acid is filtered off. Yield 5 g, m.p. 203 °C.
Phthalonic acid containing 9 carbon atoms
.CH=CH-COOH
XXXIV
.CO-COOH
COOH
XXXV
formed as a result of the next stage of oxidation68.
Oxidation
33
Naphthalene (12 kg) is heated with KMnCU (75 kg) in water (750 L) under reflux or under pressure until the color disappears. The yield of phthalonic acid is good.
Production of phthalic acid and phthalic anhydride.
Naphthalene has always been the main starting material for the production of phthalic acid and phthalic anhydride, although recently, especially in connection with the use of terephthalates in the production of polymers, the importance of three isomeric xylenes as a raw material for the production of phthalic, isophthalic and terephthalic acids has increased. The trend to replace naphthalene with xylene will intensify as the price of pure xylenes declines and the price of naphthalene rises. However, 90% of commercial phthalic anhydride is still produced from naphthalene.
At first, phthalic acid was obtained by oxidizing naphthalene with chromic or nitric acid, but at the end of the 19th century, the increasing demand for phthalic anhydride for the production of dyes served as an incentive to develop a cheaper method for its production. In 1896, BASF patented a method by which naphthalene is oxidized with 100% sulfuric acid (15 hours) in the presence of HgSO4 (0.5 hours) at 250-300 °C; the process is accompanied by the release of sulfur dioxide and carbon dioxide69. The industrial development of this cheaper method contributed to the rapid development of the production of synthetic indigoids (through phthalimnd and anthranilic acid). During the First World War, German supplies to America and Great Britain were cut off. Attempts by US chemists to master the liquid-phase method for obtaining phthalic anhydride described in the literature were unsuccessful: the average yield was only 70-25%. In 1917, the US Department of Agriculture announced the development of a catalytic vapor phase method in the laboratory. Later, this method was adopted for the organization of large-tonnage production by several companies that received the corresponding patents71. Much later, the validity of these patents was disputed by Wohl (I. G. Farbenindustry), who developed an almost identical process at the same time. As a result, the priority of his patents was confirmed72,""because in Germany the method was carried out practically a few days earlier than in the USA. In 1922, Conover and Gibbs70 (USA) reported in the press that they had developed a method by which naphthalene vapor and a fourfold excess of air were passed over a catalyst at 350-500°C; molybdenum oxide or vanadium pentoxide is used as a catalyst. In addition, a large number of other catalysts have been tested with less success.
The main areas of application of naphthalene are shown in the diagram (Fig. 16).
One of the most important areas of industrial use of naphthalene is the oxidation to phthalic anhydride. The oxidation of naphthalene is carried out by the vapor phase method on a vanadium-potassium sulfate catalyst in a stationary or fluidized bed:
4-502 - a: > + 2C02 + 2H20
The yield of phthalic anhydride on this catalyst is
86-89%, product productivity 40 kg/h per 1 m3 of catalyst. By-products of the process are 1,4-naph - toquinone, maleic anhydride, CO2.
Modification of the catalyst made it possible to increase its productivity to 50–55 kg/(h m3) and the yield of phthalic anhydride to 90–94%. The oxidation process occurs at a mass ratio of naphthalene: air = 1: 35 and a temperature of 360-370°C. The consumption of naphthalene is 1.05-1.1 tons per 1 ton of phthalic anhydride.
Badger has developed a process for the oxidation of naphthalene at a higher concentration (mass ratio of naphthalene: air - 1: 12) in a fluidized catalyst bed.
Vapor-phase oxidation of naphthalene with air at 250-450 ° C in the presence of catalysts V205, V205-A1203, Zr02, Si02-W03, B203, alkali metal phosphates also produces 1,4-naphthoquinone. V205-K2S04 modified with Fe, Sn, Si, Ti, Al oxides can be used as a catalyst.
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Rice. 16 (continued)
At a temperature of 430-480 °C, the oxidation of naphthalene occurs with a high conversion, which makes it possible to exclude the stages of separation and recycling of raw materials.
It is possible to obtain 1,4-naphthoquinone by oxidation of 1-naphthol with oxygen with a yield of 90% in the presence of the catalytic complex Co-salcomine in dimethylformamide.
1,4-Naphthoquinone is used for the synthesis of anthraquinone and its derivatives, dyes, antibacterials and fungicides.
Alkylation of naphthalene with higher linear a-olefins containing 12-20 carbon atoms produces higher alkylnaphthalenes. As catalysts, macroporous Y-type zeolites with H+ and NH4 exchange centers, the same rhenium-modified zeolites, and solid acid catalysts based on Zr02 modified with (NH4)6H4W1205 are used. The resulting monoalkylnaphthalenes are used as lubricating oils and high-temperature coolants with high thermal conductivity.
As an alkylating agent, instead of olefins, alcohols, alkyl halides can be used. Mobil Oil Corp. patented for the alkylation of naphthalene catalyst MCM-49 composition X203 nU02, where p< 35, X - трехвалентный элемент (А1, В, Fe, Ga или их смесь), Y - четырехвалентный элемент (Si, Ti, Ge или их смесь) .
In 1975, a high-temperature coolant Termolan based on higher alkylnaphthalenes was developed, manufactured by Orgsintez Production Association (Novomoskovsk). It is a liquid product with a melting point of -30-45°C, a boiling point of 450-500°C and a stable operating temperature range of -35 to 350°C. The coolant is characterized by low toxicity (maximum concentration limit = 30 mg/m3), low saturated vapor pressure (0.05-0.1 MPa at the maximum temperature of use), relatively low viscosity (60 mm2/s at 20 °C), low corrosion activity, and high radiation resistance.
Alkylnaphthalenes obtained from naphthalene and 1-eicosene or 1-docosene are used as working fluids in vacuum steam jet pumps and provide ultrahigh vacuum (2.8-4.8) ■ 10"7 Pa . Instead of individual a-olefins, the C18-C20 fraction of cracked paraffin distillate can be used for naphthalene alkylation. Alkylation of naphthalene is carried out in the presence of a BF3-H3P04-S03 catalyst at 100°C for 1 h; the yield of alkylnaphthalenes is 50-55%. Received vacuum liquid, 280
called Alkaren-1, allows creating a vacuum of about 10-7 Pa in diffusion pumps.
Based on the 180-240 °C fraction of a cracking distillate containing C8-C20 α-olefins and naphthalene, Alkaren-24 vacuum working fluid was also obtained. To avoid oligomerization, α-olefins were preliminarily hydrochlorinated in the presence of 1% (mae.) hpCl2 on silica gel. Alkylation of naphthalene with alkyl chlorides was carried out in the presence of AlCl3 at 20–100°C. Vacuum oils were also obtained by alkylation of diphenyl with C8-C12 alkyl chlorides (Alkaren D24) and C12-C14 a-olefins (Alkaren D35). The technology for producing Alkaren vacuum oils has been tested at the pilot plant of the Khimprom Production Association (Kemerovo). An important advantage of vacuum oils based on naphthalene or diphenyl and industrial mixtures of α-olefins compared to foreign analogues obtained using individual hydrocarbons is their significantly lower cost.
Alkylation of naphthalene with alcohols, for example, 2-butanol, and simultaneous sulfonation of concentrated H2804 or weak oleum, alkylnaphthalenesulfonates are obtained, which are used as surfactants. Alkylnaphthalenesulfonates are also used as anticorrosive and detergent-dispersant additives for lubricating oils.
Nitration of naphthalene with a mixture of concentrated NZh)3 and H2w04 at 50-60°C gives 1-nitronaphthalene. Impurities of 2-nitronaphthalene are 4-5% (may.) and dinitronaphthalenes - about 3% (may.). With further nitration of 1-nitronaphthalene, a mixture of 1,5- and 1,8-dinitronaphthalenes is formed.
Hydrogenation of 1-nitronaphthalene in the presence of Na or Cu gives 1-naphthylamine, the sulfonation of which produces naphthionic acid:
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The rearrangement of 1-naphthylamine hydrosulfate is carried out in the medium of o-dichlorobenzene a at 175-180 °C.
Sulfonation of naphthalene with concentrated H2S04 at a temperature of about 80 ° C leads to the formation of 1-naphthalene - sulfonic acid, and at temperatures above 150 ° C - to 2-naphthalene sulfonic acid.
Chemie AG Bitterfeld-Wolfen has patented a method for producing naphthionic acid by reacting 1 mol
1-naphthylamine and 1-1.2 mol 95-100% H2SO4 with the formation of naphthylamine hydrosulfate and its subsequent sintering with
1-1.3 mol of finely crystalline amidosulfonic acid at 160-200 °C. Naphthionic acid is isolated by heating the reaction mixture with 1 N. HC1 to boiling and purified through sodium naphthionate using activated charcoal. Purified naphthionic acid is suitable for making food colorings.
The interaction of 1-naphthylamine with aniline in the liquid phase at 230-250 ° C in the presence of 12 or /g-toluenesulfonic acid or in the vapor phase at 800 ° C over gel A1203 gives N-phenyl-1-naphthylamine (neozone A), which is used in the production of arylmethane dyes.
When nitrating 1-naphthalenesulfonic acid, a mixture of 5- and 8-nitronaphthalene-1-sulfonic acids is obtained, the reduction of which with cast-iron shavings gives the corresponding amino derivatives:
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In a similar way, Cleve's acids are obtained from 2-naphthalenesulfonic acid - a mixture of 5- and 8-aminonaphthalene-2-sulfonic acids. Naphthylaminosulfonic acids are used in the production of dyes, as well as reagents for the film and photo industry.
In two-stage sulfonation of naphthalene, first with 20% oleum at a temperature not exceeding 35°C, then with 65% oleum 282
At 55 ° C, naphthalene-1,5-disulfonic acid (Armstrong's acid) is obtained with an admixture of naphthalene-1,6-disulfonic acid.
Alkaline melting of naphthalene-2-sulfonic acid at 300-315 ° C gives 2-naphthol with a yield of up to 82%. It is possible to obtain 2-naphthol by hydroxylation of naphthalene with a 28% solution of H202, first at 50 ° C, then at 80 ° C in the presence of a catalyst - copper tetrakis (decachloro) phthalocyanine. The conversion of naphthalene is 22.3%, the selectivity of the formation of 2-naphthol is 90%.
Alkylation of naphthalene with 2-propanol in the presence of mordenite at 250 °C gives 2-isopropylnaphthalene, the oxidation of which to hydroperoxide and acid decomposition also makes it possible to obtain 2-naphthol and acetone. The maximum yield of 2-naphthol - 61% was achieved when using HC104 as a catalyst in a solution of acetic acid.
Alkylation of naphthalene with 2-propanol on H-U and LaH-U zeolites produces mainly 1-isopropylnaphthalene, from which 1-naphthol can be obtained. In industry, 1-naphthol is produced by alkaline melting of naphthalene-1-sulfonic acid with KaOH at 300 °C with a yield of about 93% or by hydrolysis of 1-naphthylamine under the action of 20% H2SO4 at 185-240 °C.
Alkylation of naphthalene with propylene or 2-propanol in the presence of H-type deposited on mordenite with a molar ratio of SiO2/Al2O3 over 15, at a naphthalene conversion of 95.2%, is accompanied by the formation of 2,6-diisopropylnaphthalene with a selectivity of 61.9%. When naphthalene is alkylated on the same mordenite zeolite with 0.5% (mae.) P1 in the presence of water additives, the conversion increases to 97.5% and the selectivity of 2,6-diisopropylnaphthalene formation to 67.3%. Impregnation of H-mordenite with cerium nitrate (at 30% (mae.) Ce) leads to an increase in selectivity for the same isomer up to 70%.
Computer Search for the Optimal Synthesis Catalyst
2,6-diisopropylnaphthalene also confirmed the choice of mordenite
During the catalytic interaction of naphthalene with di- and tri-methylnaphthalenes in the presence of zeolites, transmethylation and isomerization reactions proceed simultaneously with the enrichment of the reaction mixture with 2,6-dimethylnaphthalene.
Alkylation of naphthalene with methanol using zeolite H-gvM-b results in the formation of 2-methylnaphthalene. The mechanism of P-selective methylation is explained by the fact that 1-methylnaphthalene molecules, which have a larger volume, do not penetrate into the channels of the zeolite. With further methylation of 2-methylnaphthalene on ZSM-5 zeolite, especially when its outer surface is poisoned with 2,4-dimethylquinoline, 2,6-dimethylnaphthalene is selectively formed.
Similar methods can be used to obtain 2,6-diethylnaphthalene. Alkylation of naphthalene with ethylene or ethyl halide in the presence of zeolites gives predominantly 2,6-diethylnaphthalene, which is purified by crystallization or chromatography on a Y-type zeolite modified with Na, K or Ba ions.
Nippon Steel Chemical Co. patented the process of obtaining 2,6-diethylnaphthalene by the interaction of naphthalene or 2-ethylnaphthalene with polyethylbenzenes in the presence of zeolite U. So, when 2-ethylnaphthalene was reacted with tetraethyl-benzenes at 80 ° C, a conversion of 2-ethylnaphthalene of 82.7% was achieved after 2 hours, the yield of diethylnaphthalenes was 62.3 %, their composition, %:
2.6-50.1; 2.7-24.8; 1.6-15; 1.7-5.3; other isomers 4.8 . Oxidation of 2,6-dialkylnaphthalenes gives 2,6-naphthalenedicarboxylic acid.
Hydrogenation of naphthalene in the presence of nickel catalysts at 150°C leads to the formation of tetralin, and at 200°C to a mixture of cis- and trans-decalins. The yield of decalins is about 95% upon hydrogenation of tetralin on a platinum-aluminophosphate catalyst supported on A1203 at a process temperature of 220°C and a pressure of 5.17 MPa. An effective catalyst for the hydrogenation of naphthalene to decalins - 0.1% (mae.) Ru on mixed oxides Mn203-Ni0.
Hydrogenation of tetralin to cis - and mpawc-decalin takes place in high yield in a two-phase system, including a catalyst - chlorine(1,5-hexadiene)rhodium dimer and an aqueous buffer solution with surfactant. The catalyst remains highly active after 8 cycles.
Tetralin and decalin are recommended to be used instead of 100-200 aromatic solvents - dangerous air pollutants. They are used in paints and inks, pharmaceuticals, and agrochemicals. Tetralin and decalin are produced, in particular, by the American company Koch Specialty Chemicals at a plant in Corpus Christi, pc. Texas. In Russia, tetralin is produced by OAO "Torzhok Plant of Printing Inks" in Tver Oblast.
Based on alkyltetralins, medium-alkaline sulfonate additives for motor oils are obtained.
Liquid-phase chlorination of naphthalene in the presence of FeCl3 gives 1-chloronaphthalene with impurities of 2-chloro-, 1,4- and 1,5-di-chloronaphthalenes. Chlorination of molten naphthalene also produces a mixture of tri- and tetrachloronaphthalenes - halo-wax. Galovax is used as a phlegmatizer, substitute for wax and resins in the impregnation of fabrics, wire insulation, and the manufacture of capacitors.
When naphthalene is acetylated with acetic anhydride in dichloroethane or chlorobenzene, one obtains with a yield of 98%
1-acetylnaphthalene, and when carrying out the reaction in a nitrobenzene medium - 2-acetylnaphthalene with a yield of about 70%. 2-Acetyl - naphthalene is used as a fragrant and odor fixative in the preparation of fragrances for soaps and perfume compositions.
When 1-acetylnaphthalene interacts with sodium polysulfide, a red-brown thioindigoid dye is obtained:
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Thioindigoid dyes are more resistant than indigoid dyes to the action of oxidizing agents and alkalis and are used for printing on cotton, linen, viscose, for vat dyeing of wool and fur, as pigments in printing.
In substitution reactions in naphthalene derivatives, the introduction of an electrophilic particle occurs in accordance with the following rules:
1) The electron-donating group directs the electrophilic reagent to the ring in which it is located. If this group is in position 1, the electrophilic species replaces the hydrogen in position 2 or in position 4, the electron donating group in position 2 directs the electrophilic species to position 1.
2) An electron-withdrawing group sends an electrophilic reagent to another unsubstituted ring (to position 5 or 8 in halogenation and nitration).
This direction of substitution can be explained as follows. The orientant has the greatest influence on the ring with which it is associated. Therefore, the most successful attack by the electrophile E is on the ring with the electron donor group G, in which the positive charge can be better distributed.
Recovery and oxidation of naphthalene
When naphthalene is oxidized in the presence of vanadium pentoxide, one ring is destroyed and phthalic anhydride is formed.
Naphthalene is oxidized with a mixture of K 2 Cr 2 O 7 and H 2 SO 4 to phthalic acid.
If there is a substituent in one of the rings, then the ring with an increased electron density is oxidized.
Unlike benzene, naphthalene can be reduced with chemical reducing agents.
The benzene ring in tetralin is reduced only under harsh conditions.
Anthracene and phenanthrene
Anthracene and phenanthrene are aromatic compounds. They are flat cyclic structures containing a closed p- electron cloud located above and below the plane of the rings. Number p- electrons according to Hückel's rule is 4n + 2 = 4 × 3 + 2 = 14.
Anthracene can be considered as a resonant hybrid of structures I-IV.
Its resonance energy is 352 kJ/mol.
Phenantrene can be represented as a resonant hybrid of structures V-IX.
The resonant energy of phenanthrene is 386 kJ/mol.
Anthracene and phenanthrene enter into electrophilic substitution reactions. Their active positions 9 and 10 are in the middle ring, since attacking these positions preserves the aromaticity of the two side benzene systems with a resonance energy of 153×2=306 kJ/mol. When attacking the side rings, the aromaticity of one naphthalene fragment with a resonance energy of 256 kJ/mol is retained.
The conclusion about the activity of positions 9 and 10 is valid both for electrophilic substitution and for oxidation and reduction reactions.
Oxidation. The benzene ring, due to its special stability, is resistant to most oxidizing agents. However, the alkyl groups attached to the ring are readily oxidized by oxidizing agents such as sodium dichromate in an acid medium, chromium(VI) oxide in acetic acid, or potassium permanganate. As a result, products of oxidative degradation of side chains are formed - aromatic carboxylic acids:
During oxidation with chromium trioxide in acetic anhydride, the methyl group of alkylarenes is oxidized to an aldehyde group; further oxidation to acid is prevented by the formation of diacetate, which is stable under these conditions. Acid-catalyzed hydrolysis in aqueous alcohol leads to an aromatic aldehyde:
Benzyl alcohols are smoothly oxidized to aldehydes when freshly precipitated manganese dioxide is used as an oxidizing agent:
Oxidation of condensed aromatic hydrocarbons results in different products depending on the reagent used and the reaction conditions. Reagents based on chromium (VI) in an acid medium oxidize naphthalene and alkylnaphthalenes to naphthoquinones, while sodium dichromate in an aqueous solution oxidizes only alkyl groups. The oxidation of naphthalene with potassium permanganate in an alkaline medium is accompanied by the destruction of one aromatic ring with the formation monocyclic dicarboxylic acids: 
Anthracene is smoothly oxidized with sodium bichromate in sulfuric acid or chromium (VI) oxide in acetic acid to anthraquinone:
Hydrogenation. Although the aromatic ring of benzene is hydrogenated under much harsher conditions than the double or triple bond of alkenes and alkynes, benzene and its derivatives can be hydrogenated to derivatives cyclohexane over Raney nickel (T 120-150 o and pressure 100-150 atm). The platinum group catalysts are more efficient, among which the best are rhodium or ruthenium deposited on alumina.
Hydrogenation of dialkylbenzenes with Rh or Ru usually produces mainly cis- isomer. Hydrogenation on Raney nickel is not stereoselective; a mixture is always formed cis-, trance-isomers. The catalytic hydrogenation of the benzene ring cannot be stopped at the first or second stage, since cyclohexadienes and cyclohexenes are hydrogenated at a faster rate than aromatic compounds.
Birch Recovery. The aromatic ring of arenes can be reduced with a solution of sodium in liquid ammonia in the presence of alcohol as a protonating agent. In this case, benzene is reduced to non-conjugated cyclohexadiene-1,4: (note 44),
For this reaction, a mechanism has been proposed that includes the sequential formation of a radical anion, a radical, and an anion of cyclohexadiene:
