Hydrogenation of anthraquinone

R. Haider, A. Lawal, Experimental studies on hydrogenation of anthraquinone derivative in a microreactor, Catal. Today 2007, 125, 48-55. 

Hydrogenation of aromatic compounds (dearomatization), that is, hydrogenation of henzene, toluene, and polyaromatics Hydrogenation of anthraquinone in the production of H2O2... 

Traditionally, monolith reactors have demonstrated their performance in gas-phase reactions, particularly in the treatment of automotive exhaust gases. Today, virtually all vehicles are equipped with catalytic converters. Here we will consider three-phase applications. These have been studied by a few authors and research groups such as Moulijn and coworkers [4,5] and Irandoust and Andersson [6]. Certain industrial processes such as hydrogenation of anthraquinone in the production of hydrogen peroxide are also examples of the monolith reactor technology being established on an industrial scale. Monolith... 

Takahax A variation of the Stretford process for removing hydrogen sulfide from gas streams, in which naphthaquinone sulfonic acid is used in place of anthraquinone disulfonic acid. Four variants have been devised types A and B use ammonia as the alkali, types C and D use sodium hydroxide or carbonate. Developed by the Tokyo Gas Company and licensed in the United States by Ford Baken and Davis, Dallas, TX. Many plants are operating in Japan. 

Electron-donating groups (amino, methylamino, hydroxy, methoxy) in the 2-position, on the other hand, are extremely undesirable because, unlike similar substituents in the 1,4-positions, they are unable to form intramolecular hydrogen bonds with the keto groups of anthraquinone and hence are highly susceptible to photo-oxidation [167]. 

In general, 1-substituted derivatives of anthraquinone are more bathochromic than the corresponding 2-substituted isomers, in accordance with PPP-MO calculations [1]. Intramolecular hydrogen bonding is not possible between the carbonyl group and a 2-... 

The mechanism for the addition of 50 to anthraquinone (Scheme 52), 1,4-diacetylbenzene (Scheme 53), and 1,2-diacetylbenzene (Scheme 54) has been proposed.326 The addition of 50 to benzophenone followed by reaction with Wilkinson s catalyst formally results in the hydrogenation of a double bond (Equation (262)).325 This species also undergoes stereospecific inertion into the vinyl chloride bond of various halogenated alkenes with high yields in most cases (Equations (263)-(267)).329... 

The most important method of making hydrogen peroxide is by reduction of anthraquinone to the hydroquinone, followed by reoxidation to anthraquinone by oxygen and formation of the peroxide. R is usually ethyl but /-butyl and jec-amyl have also been used. 

This study indicates that the oxidation of dihydroanthracene in a basic medium involves the formation of a monocarbanion, which is then converted to a free radical by a one-electron transfer step. It is postulated that the free radical reacts with oxygen to form a peroxy free radical, which then attacks a hydrogen atom at the 10-position by an intramolecular reaction. The reaction then proceeds by a free-radical chain mechanism. This mechanism has been used as a basis for optimizing the yield of anthraquinone and minimizing the formation of anthracene. 

The resulting red solution is quickly filtered by suction, and hydrogen peroxide is added to the filtrate until a yellow precipitate appears. Dilute hydrochloric acid is added until the mixture is acidic to litmus, and the precipitate is collected by suction filtration, washed well with water, and air-dried. Five to seven grams of anthraquinone, m.p. 280-283°, may thus be obtained. 

Subsequent one-electron transfer and intramolecular hydrogen migration lead to radical 102 followed by reaction with 02 to yield hydroperoxide radical 103. Radical 103 is further oxidized to a dihydroperoxide (104), which decomposes to anthra-quinone. Alternatively, 103 may be transformed to a diradical that eventually gives anthracene as a byproduct. The ratio of the two products strongly depends on the solvent used. The highest yield of anthraquinone (85% at 100% conversion) was achieved in 95% aqueous pyridine. 

Rhodium(II) acetate catalyzes C—H insertion, olefin addition, heteroatom-H insertion, and ylide formation of a-diazocarbonyls via a rhodium carbenoid species (144—147). Intramolecular cyclopentane formation via C—H insertion occurs with retention of stereochemistry (143). Chiral rhodium (TT) carboxamides catalyze enantioselective cyclopropanation and intramolecular C—N insertions of CC-diazoketones (148). Other reactions catalyzed by rhodium complexes include double-bond migration (140), hydrogenation of aromatic aldehydes and ketones to hydrocarbons (150), homologation of esters (151), carbonylation of formaldehyde (152) and amines (140), reductive carbonylation of dimethyl ether or methyl acetate to 1,1-diacetoxy ethane (153), decarbonylation of aldehydes (140), water gas shift reaction (69,154), C—C skeletal rearrangements (132,140), oxidation of olefins to ketones (155) and aldehydes (156), and oxidation of substituted anthracenes to anthraquinones (157). Rhodium-catalyzed hydrosilation of olefins, alkynes, carbonyls, alcohols, and imines is facile and may also be accomplished enantioselectively (140). Rhodium complexes are moderately active alkene and alkyne polymerization catalysts (140). In some cases polymer-supported versions of homogeneous rhodium catalysts have improved activity, compared to their homogenous counterparts. This is the case for the conversion of alkenes direcdy to alcohols under oxo conditions by rhodium—amine polymer catalysts... 

Figure 6.10 Two examples of free radical photoinitiation reactions dissociation of dioxolane and hydrogen atom abstraction of anthraquinone in tetrahydrofuran...

The quantum yield of the primary hydrogen abstraction process is unity, and is independent of irradiation wavelength, light intensity and temperature. Its wavelength range follows of course the absorption spectrum of anthraquinone so that this actinometer is particularly well suited for the UV region. 

Reaction LXX. Oxidation of certain Hydrocarbons. (B., 14, 1944 A. Spl., 1869, 300 E.P., 1948 (1869).)—This reaction is confined in the aliphatic series almost exclusively to the replacement by hydroxyl of the hydrogen attached to tertiary carbon atoms. A powerful oxidising agent, e.g., chromic acid in glacial acetic acid, is necessary. In the aromatic series the reaction is somewhat more easy to accomplish when the sodium salt of anthraquinone-jS-monosulphonic acid, for example, is fused under pressure with caustic soda and a little potassium chlorate, replacement of both a hydrogen atom and the sulphonic acid group by hydroxyl occurs, and alizarin ( /f-dihydroxyanthraquinone) is obtained. 

The hydrogenation of 2-ethyl-5,6,7,8-tetrahydroanthraqumone (THEAQ) at the oxygen in the presence of a palladium supported catalyst is a key step in the industrial production of hydrogen peroxide. In industrial plants, the performance of the catalyst slowly decreases because of deactivation. Two types of catalyst poisoning are operative, a reversible one, related to the presence of water, and a permanent one, probably due to the condensation of two or more anthraquinone molecules on the palladium surface. The kinetic data obtained from laboratory runs are used to simulate the performance in industrial plants. 

The hydrogenation of THEAQ is a zero-order reaction with respect to hydrogen and a first order reaction with respect anthraquinone [2]. The kinetics of the catalyst deactivation has been studied in a laboratory continuous reactor. Two deactivation mechanisms have been recognized, a reversible and fast one due to the presence of water a d a permanent and slow one probably due to the formation of... 

The well-known photochromic transformations of anthraquinones are closely associated with the photoinduced migration of hydrogen, acyl, or aryl groups. Although photochromism of these compounds fits the reaction shown in Scheme 9, the processes of photochromic transformation exhibit some features related to the nature of the photoreactive state and details of the mechanism of the photochromic transformations. 

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