Anthraquinone purification

WorkingS olution Regeneration and Purification. Economic operation of an anthraquinone autoxidation process mandates fmgal use of the expensive anthraquinones. During each reduction and oxidation cycle some finite amount of anthraquinone and solvent is affected by the physical and chemical exposure. At some point, control of tetrahydroanthraquinones, tetrahydroanthraquinone epoxides, hydroxyanthrones, and acids is required to maintain the active anthraquinone concentration, catalytic activity, and favorable density and viscosity. This control can be by removal or regeneration. 

In Europe, where an abundant supply of anthracene has usually been available, the preferred method for the manufacture of anthraquinone has been, and stiU is, the catalytic oxidation of anthracene. The main problem has been that of obtaining anthracene, C H q, practically free of such contaminants as carbazole and phenanthrene. Many processes have been developed for the purification of anthracene. Generally these foUow the scheme of taking the cmde anthracene oil, redistilling, and recrystaUizing it from a variety of solvents, such as pyridine (22). The purest anthracene may be obtained by azeotropic distillation with ethylene glycol (23). 

Has been purified by co-distillation with ethylene glycol (boils at 197.5°), from which it can be recovered by additn of water, followed by crysm from 95% EtOH, benzene, toluene, a mixture of benzene/xylene (4 1), or EtjO. It has also been chromatographed on alumina with pet ether in a dark room (to avoid photo-oxidation of adsorbed anthracene to anthraquinone). Other purification methods include sublimation in a N2 atmosphere (in some cases after refluxing with sodium), and recrystd from toluene [Gorman et al. J Am Chem Soc 107 4404 1985]. 

Recovery experiments were conducted with the following standards, which were used as received without further purification 5-chlorouracil (Calbiochem), furfural (Aldrich), crotonaldehyde (Aldrich), caffeine (Aldrich), isophorone (Aldrich), 2,4-dichlorophenol (Aldrich), anthraquinone (Aldrich), biphenyl (Ultra Scientific), 2,4 -dichlorobiphenyl (Ultra Scientific), 2,6-bis(l,l-dimethylethyl)-4-methylphenol (Aldrich), 2,2, 5,5 -tetrachlorobiphenyl (Ultra Scientific), benzo[e]pyrene (Aldrich), bis(2-ethylhexyl) phthalate (Scientific Polymer Products), 4-methyl-2-pentanone (Aldrich), quinoline (Kodak), 1-chloro-dodecane (Eastman), stearic acid (Kodak), quinaldic acid (Aldrich), trimesic acid (Aldrich), glucose (Aldrich), glycine (Aldrich), and chloroform (Burdick and Jackson). 

To remove the feedback regulation mechanism and to avoid product degradation various adsorbents have been used for the in situ separation of plant cell cultures as shown in Table 1. In situ removal with polymeric adsorbents stimulated anthraquinone production more than the adsorbent-free control in Cinchona ledgeriana cells [35]. It was found that nonionic polymeric resins such as Amberlite XAD-2 and XAD-4 without specific functional groups are suitable for the adsorption of plant metabolite [36]. The use of the natural polymeric resin XAD-4 for the recovery of indole alkaloids showed that this resin could concentrate the alkaloids ajmalicine by two orders of magnitude over solvent extraction [37] but the adsorption by this resin proved to be relatively nonspecific. A more specific selectivity would be beneficial because plant cells produce a large number of biosynthetically related products and the purification of a several chemically similar solutes mixture is difficult [16]. 

In addition to quinone reduction and hydroquinone oxidation, electrode reactions of many organic compounds are also inner-sphere. In these charge transfer is accompanied by profound transformation of the organic molecules. Some reactions are complicated by reactant and/or product adsorption. Anodic oxidation of chlorpro-mazine [54], ascorbic acid [127], anthraquinone-2,6-disulfonate [128], amines [129], phenol, and isopropanol [130] have been investigated. The latter reaction can be used for purification of wastewater. The cyclic voltammogram for cathodic reduction of fullerene Cm in acetonitrile solution exhibits 5 current peaks corresponding to different redox steps [131]. 

ZnTPP (Hambright, Washington D.C.), duroquinone (DQ) (Aldrich) and methyl viologen (MV+2) (BDH CHEMICALS) were used without further purification. The sodium salt of anthraquinone 2-sulphonate (AQS) (BDH CHEMICALS) was recrystalized from methanol. Benzyldimethyl-n-hexadecylammonium chloride (BHDC) (BDH CHEMICALS) was dried over P205 and stored under vacuum. The solvent, benzene (pro-analysis) (BDH CHEMICALS) was dried and distilled over sodium wire. Stock solutions of reversed micelles were prepared by adding dropwise the calculated amount of water to the appropriate solution of BHDC. The surfactant concentration used throughout the experiments was 0.1 mol dm 3. 

In this paper solubility measurements of synthetic and natural dyestuffs are presented using VIS-spectroscopy. The investigations concentrate on two different methods. I. P-carotene was measured as a function of temperature and pressure in near- and supercritical C02 (289 to 309 K, 10 to 160 MPa) and CC1F3 (297 to 326 K, 12 to 180 MPa), respectively, using a static method. II. Additionally, the solubilities of l,4-bis-(n-alkylamino)-9,10-anthraquinones (with n-alkyl = butyl, octyl) were determined with a dynamic method in temperature and pressure ranges from 310 to 340 K and 8 to 20 MPa, respectively this method permits a continuous purification from better soluble impurities as well as the measurement of solubilities at the same time. For both anthraquinone dyestuffs intersection points of the solubility isotherms were found in the plot of concentration versus pressure. This behavior can be explained by a density effect. 

Recently additional measurements on some of these anthraquinone dyes were carried out with a dynamic method using a supercritical fluid chromatography (SFC) technique. This method permits the measurement of solubilities as well as the continuous purification from better soluble impurities which might cause serious errors in the solubility data (see section 3.). 

The dynamic method permits the purification from better soluble impurities as well as continuous solubility measurements at the same time. An adsorption effect of the stationary phase which is used to precipitate the dyestuff on its surface is not found within the experimental accuracy. The measurements of l,4-bis-(n-alkylamino)-9,10-anthraquinone (with n-alkyl = butyl, octyl) show two intersection points in the plot of pressure versus concentration. 

The crude anthraquinone contains some unchanged anthracene and other impurities and must be purified before use. Purification is effected by partial sulfonation and distillation with superheated steam. 

Hemwimon S. Pavasant P. Shotipruk A. 2007. Microwave-assisted extraction of antioxidative anthraquinones from roots of Morinda citrifolia. Sep. Purif. Technol. 54 44-50. 

In principle, process integration applies even more to direct synthesis of hydrogen peroxide, further improving the advantages over the anthraquinone route. Methanol can be used to replace water as the solvent and the dilute methanol solution obtained fed into the epoxidation reactor. Minimal purification may be required, for example for the removal of hydrogen bromide and other additives that may have been needed to increase the selectivity. 

For the manufacture of alizarin on a large scale a very pure anthraquinone is required, and this is generally prepared by oxidation of anthracene with sodium bichromate and dilute sulphuric acid. The anthracene is generally a 50-per-cent, product which has oeen converted into a soft powder by subliming with superheated steam. The oxidation takes place in lead-lined vessels in which the mixture is heated by direct steam. By employing a pure anthracene and a not too concentrated oxidation-mixture, the anthraquinone separates as soft grey powder, which is freed from acid by washing wdth water. The crude product is then dried, dissolved in concentrated sulphuric acid, and precipitated with water. A further purification is effected by sublimation with superheated steam. 

Experiments with Anthraquinone.—The anthraquinone used was Kahl-baum s purest grade and was used without further purification Since... 

As a typical improvement, let us consider anthraquinone (AQ) synthesis [Eq. (33)]. This important product is classically and industrially obtained by cyclodehydration of o-benzoylbenzoic acid in boiling concentrated sulfuric acid for several hours (> 8 h at 170°C). These conditions lead to many problems, be it handling, treatment, AQ purification or generation of polluting wastes. 

Totally 16 different dyes were used without purification in this preliminary test including 4 anthraquinone dyes, 7 azo dyes, 2 metal containing (Copper and Chromium) azo dyes, 2 cyanine dyes and 1 stilbene azo dye. Dyes were UV-irradiated under UV light at 253.7 nm. 

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