Sulfonation of anthraquinone

Dyes, Dye Intermediates, and Naphthalene. Several thousand different synthetic dyes are known, having a total worldwide consumption of 298 million kg/yr (see Dyes AND dye intermediates). Many dyes contain some form of sulfonate as —SO H, —SO Na, or —SO2NH2. Acid dyes, solvent dyes, basic dyes, disperse dyes, fiber-reactive dyes, and vat dyes can have one or more sulfonic acid groups incorporated into their molecular stmcture. The raw materials used for the manufacture of dyes are mainly aromatic hydrocarbons (67—74) and include ben2ene, toluene, naphthalene, anthracene, pyrene, phenol (qv), pyridine, and carba2ole. Anthraquinone sulfonic acid is an important dye intermediate and is prepared by sulfonation of anthraquinone using sulfur trioxide and sulfuric acid. 

SuIfona.tlon, Sulfonation is a common reaction with dialkyl sulfates, either by slow decomposition on heating with the release of SO or by attack at the sulfur end of the O—S bond (63). Reaction products are usually the dimethyl ether, methanol, sulfonic acid, and methyl sulfonates, corresponding to both routes. Reactive aromatics are commonly those with higher reactivity to electrophilic substitution at temperatures > 100° C. Tn phenylamine, diphenylmethylamine, anisole, and diphenyl ether exhibit ring sulfonation at 150—160°C, 140°C, 155—160°C, and 180—190°C, respectively, but diphenyl ketone and benzyl methyl ether do not react up to 190°C. Diphenyl amine methylates and then sulfonates. Catalysis of sulfonation of anthraquinone by dimethyl sulfate occurs with thaHium(III) oxide or mercury(II) oxide at 170°C. Alkyl interchange also gives sulfation. 

In 1901, mercury cataly2ed a-sulfonation of anthraquinone was discovered, and this led to the development of the chemistry of a-substituted anthraquinone derivatives (a-amino, a-chloro, a-hydroxy, and a,a -dihydroxyanthraquinones). In the same year R. Bohn discovered indanthrone. Afterward flavanthrone, pyranthrone, and ben2anthrone, etc, were synthesi2ed, and anthraquinone vat dyes such as ben2oylaniinoanthraquinone, anthrimides, and anthrimidocarba2oles were also invented. These anthraquinone derivatives were widely used to dye cotton with excellent fastness, and formed the basis of the anthraquinone vat dye industry. 

Sulfonation of anthraquinone to form the 1-sulfonic acid is achieved at approximately 120°C with 20% oleum in the presence of mercury or a mercury salt as a catalyst [2], Without this catalyst, the reaction produces the 2-sulfonic acid. Exchange with aqueous ammonia (30%) at about 175°C under pressure converts the potassium salt of 1-sulfonic acid to 1-aminoanthraquinone in 70 to 80% yield. To avoid sulfite formation, the reaction is performed in the presence of an oxidant, such as m-nitrobenzosulfonic acid, which destroys sulfite. 

Prior to the discovery of a-sulfonation of anthraquinone, nitration was the only useful method for preparing a-substituted anthraquinones. The nitro group of a-nitroanthraquinones can be replaced in a manner similar to the sulfonic acid moiety, e.g., by chlorine atoms and amino, hydroxy, alkoxy, or mercapto groups. Reduction readily yields aminoanthraquinones. Nitration of anthraquinone has gained increasing importance because of environmental considerations, this method offering an economical alternative to a-sulfonation... 

An interesting example of a reaction with a ketone is the sulfonation of anthraquinone. Many. dyestuffs contain this unit and the sulfonate group makes them soluble in water. Oleum at 160°C must be used for the sulfonation, which goes in one of the four equivalent positions on the two benzene rings, meta to one carbonyl group but para to the other. 

By contrast, the sulfonation of anthraquinone requires oleum and no more than two sulfonic acid groups can be introduced. In this system, sulfonation in the a-position requires the use of HgO as a catalyst. Examples of the... 

Fig. 13.58. Typical products produced from the sulfonation of anthraquinone.

Previously, this was done with pyrolusite, but modem processes use arsenic acid (with 2-aminoanthraquinone) and sodium m-nitrobenzenesulfonate (with 1-amino-anthraquinone). The sulfite can ako be removed by precipitation with alkaline earth chlorides, e.g., barium chloride. The procedure given above has the advantage that it yields a product which is practically ash-free. The ammonium chloride is added to neutralize the alkali formed in the reaction (the arsenite forrned acts as free sodium hydroxide). The mother liquors, which contain arsenious acid, are poisonous, of course, and must be handled carefully. They are usually treated with milk ef lime to render them harmless. The toxicity of such waste products is frequently ovo emphasized if they are discharged into large streams, for example, ftey rarely poison the fish. In plant operations, the excess anunonia is collected and used over without further treataent For a general discussion of the sulfonation of anthraquinone, see page 56 ff. 

The most important derivative employed in vat dye manufacture is the reduction product of 2-nitroanthraquinone, namely 2-aminoanthraquinone (61). It was formerly manufactured from the 2-sulfonic acid of anthraquinone, by reaction with ammonia in the presence of oxygen. However, sulfonation of anthraquinone requires mercury and the subsequent animation requires arsenic, making these processes ecologically unattractive. From the early 1970s, processes for direct nitration of anthraquinone at the 2-position, followed by reduction, were introduced, mainly as a result of research in Japan45,46. 

Reaction of a liquid with a solid, as the sulfonation of anthraquinone. 

Schemes 9-3 and 9-4 are sequences of two substitutions, first a metallo-de-hydrogenation, followed by a halogeno-de-metallation. Scheme 9-3 is analogous to the well known electrophilic aromatic sulfonation of anthraquinone in position 1. This isomer is obtained only if the reaction is run in the presence of catalytic amounts of mercury (ii) salts. Nowadays, however, larger effort is devoted to either replace mercury by other catalysts, or in the search for processes leading to (practically) complete recovery of the mercury. This case raises two questions with respect to the reaction sequence (9-3) first, whether it is possible to apply a one-pot process with catalytic amounts of a mercury compound (not necessarily HgO) to the synthesis of compounds 9.5, and second, whether mercury can be completely recycled in processes using either stoichiometric or catalytic amounts of the element.

The observation of Schollkopf and coworkers, that the mercury method is applicable to a-diazo- 8-carbonyl compounds, but not to diazomethane, is likely to be due to the same reason as the selective sulfonation of anthraquinone in the 1-position. The mercury ion approaches the reacting CH group via a complex with the O-atom of the neighboring carbonyl group. Mercuration of a-diazo- ff-carbonyl compounds and of anthraquinone are different, however, in another aspect, namely substitution by the metal takes place at the C-atom neighboring the carbonyl group... 

One year after the structure elucidation of alizarin, Heinrich Caro at BASF developed in collaboration with Graebe and Liebermann the following successful synthesis. Sulfonation of anthraquinone with oleum [56] gives in the absence of catalysts, on steric grounds, anthraquinone-2-sulfonic acid [57] as the main product. This intermediate is then subjected to an alkali melt under oxidative conditions. 

The sulfonation of anthraquinone to produce anthraquinone-l-sulfonic add is carried out under relatively mild conditions in the presence of mercury (0.5%) with 20% oleum. To avoid disulfonation, the reaction is restricted to a conversion of only 50%, and at a temperature of 120 °C. Anthraquinone is soluble in oleum, pro-... 

The discovery that the sulfonation of anthraquinone, which normally occurs in the /3-position, is directed exclusively to the a-position by a small amount of mercury has prompted investigations of the effect of mercury on other sulfonations. No instances have been found in which the course of the reaction of hydrocarbons is altered drastically. The sulfonation of naphthalene and of anthracene is unaffected. However, the course of the reaction of sulfur trioxide-sulfuric acid with o-xylene, o-dichlorobenzene, and o-dibromobenzene is affected to a certain extent. The 4-sulfonic acid is the exclusive product of sulfonation in the absence of mercury the 3-sulfonic acid is formed to the extent of 20-25% in the presence of 10% of mercury. The relative ineffectiveness of mercury in the sulfonation of hydrocarbons is understandable if it is true that the activity of mercury in the reactions of oxygen-containing compounds is due to mercuration followed by replacement with the sulfonic acid grouping. Phenols are known to be particularly susceptible to mercuration (in the ortho position), and mercury has been found to exert some effect in the sulfonation of phenols, such as a-naphthol. ... 

---