Subject Anthraquinones

Mechanism of Anthraquinone Acceleration. The mechanism for the dual function of AQ has been the subject of much research (29). Anthraquinone is an effective pulping accelerator in very small quantities and functions as a catalyst in the process. It is generally accepted that AQ functions in a complex redox sequence. 

In a recent study of twenty disperse and solvent dyes, data for water solubility, octanol/ water partition coefficient, entropy of fusion and melting point were subjected to regression analysis. Complicating factors such as impurities, polymorphism, tautomerism, polarisation and hydrogen bonding precluded the development of reliable predictions of solubility and partition coefficient. Anthraquinone dyes exhibited much lower entropy of fusion than many of the azo dyes [64,65]. 

Electrophilic substitution at the anthraquinone ring system is difficult due to deactivation (electron withdrawal) by the carbonyl groups. Although the 1-position in anthraquinone is rather more susceptible to electrophilic attack than is the 2-position, as indicated by jt-electron localisation energies [4], direct sulphonation with oleum produces the 2-sulphonic acid (6.3). The severity of the reaction conditions ensures that the thermodynamically favoured 2-isomer, which is not subject to steric hindrance from an adjacent carbonyl group, is formed. However, the more synthetically useful 1-isomer (6.7) can be obtained by sulphonation of anthraquinone in the presence of a mercury(II) salt (Scheme 6.4). It appears that mercuration first takes place at the 1-position followed by displacement. Some disulphonation occurs, leading to the formation of the 2,6- and 2,7- or the 1,5- and 1,8-disulphonic acids, respectively. Separation of the various compounds can be achieved without too much difficulty. Sulphonation of anthraquinone derivatives is also of some importance. 

Anthracene was oxidized to anthraquinone. dibrominated, and the dibromo derivative subjected to a caustic fusion. Alizarin was obtained in an impure form and in low yield. This represented the first synthesis of a natural dye. 

Methyl anthraquinone has been obtained by the oxidation of /3-methyl anthracene by several investigators 1 and material of the same origin, obtained by the benzene-extraction of crude commercial anthraquinone,2 has been fully described. As regards the synthesis from phthalic anhydride and toluene, both the preparation and properties of />-toluyl-o-benzoic acid 3 and the complete synthesis 4 have been the subject of several papers. This acid has also been prepared from o-carbomethoxy benzoyl chloride and toluene.5 The phthalic anhydride synthesis of anthraquinone derivatives in general has received considerable attention. An account of this work, together with extensive references, is given by Barnett.6... 

Anthraquinone derivatives substituted in the 1,5-positions should be subject to steric strain because of the close approach of the substituent groups to the quinonoid oxygen atoms. Several anthraquinone derivatives have been examined crystallographically. The structure of the parent molecule (62) (Sen, 1948) has been refined by Murty (1960) and is planar to within 0-01 A. 

Figure 3. Ultraviolet spectrum of anthraquinone adsorbed on zeolite subjected to thermal treatment in vacuum at 300°C (1) NaY (2) sample 1 with adsorbed anthraquinone after ultraviolet irradiation (3) CaX (4) HY (5) sample 4 with adsorbed anthraquinone after ultraviolet irradiation...

The Sharpless regioreversed asymmetric aminohydroxylation protocol was used as a key step in the total synthesis of ustiloxin D by M.M. Joullie and co-workers.The ( )-ethyl cinnamate derivative was subjected to in situ generated sodium salt of the N-Cbz chloroamine in the presence of catalytic amounts of the anthraquinone-based chiral ligand to afford the desired A/-Cbz protected (2S,3R)-(3-hydroxy amino ester in good yield and with good diastereoselectivity. 

The easily available protected phenol ether 83 was subjected to anodic oxidation (-bl.3 V V5. SCE) in MeOH containing NaOAc and LiC104 as a supporting electrolyte to afford in 53% yield quinone monoketal 84, which reacted with 5-fluoro-3-cyanophthalide (85) in the presence of LDA to give anthraquinone 86. This quinone was converted... 

As already shown in Scheme 16, the electrochemically generated /t-quinone monoacetal (84) reacted with 3-cyanophthalide anion 85 to give the anthraquinone 86. Similarly, PhI(OAc)2-promoted oxidation of 4-substituted phenols in MeOH provides the corresponding cyclohexa-2,5-dienones, which react with the anion of 3-cyanophthalide to yield a variety of anthraquinones . A-Acetyltyrosine ethyl ester 456 was subjected to... 

Kortiim and Braun (118) found that a ground-up mixture of silica-gel or AljOs with solid anthracene subjected to ultraviolet irradiation in open air displays very rapidly a new absorption band at 275 m.fi (in diffusely reflected light) and acquires on further exposure a yellow-brown coloration. In similar mixtures with MgO and KCl the photooxygenation of anthracene is much slower, which indicates a specificity of silica gel. It could be spectrally shown that anthraquinone is a primary product giving on further exposure 1,4-dihydroanthraquinone (quinizarine), which could be eluted, producing a red solution with an absorption maximum close to that observed on silica-alumina, as just mentioned above. 

These few examples give some small indication of the chemistry of the Indigoid and Anthraquinone vat dyes, but the subject covers a wide range and the molecular structure of many is far from simple. For further information, Fox J.S.D.C., 1949, 65, 508), Bradley (R.I.C. Special Publication, No. 5, 1958), or Thomson J.S.D.C., 1936, 52, 237 and 247), should be consulted. 

Among these aromatics, only anthraquinone has subjected to further studies and will be considered in some detail here. 

The relative proportions in which the products, chiefly benzaldehyde, benzoic acid, and anthraquinone, are obtained depends in a large measure on the temperatures to which the reaction mixture of toluene vapor and air is subjected. High temperatures, together with rapid rates of flow as well as high temperatures and mild catalysts, are conducive to bai-zaldehyde formation. With vanadium pentoxide catalysts oxidation of... 

Photosensitized crosslinking of polymers has been the subject of numerous publications [l - 30], concerned mainly with poly(ethylene), poly(vinyl alcohol), various vinyl copolymers, copolymers of maleic anhydride and/or phtalic anhydride with styrene and some polymers derivated from cinnamic acid. The following compounds were used as sensitizers benzophenone, 4-chloro- and 4,4-dimethylbenzophenone [l, 3-6, 8, 9l, oC -and -derivatives of anthraquinone [3, 23] acetophenone, hydroquinone, triphenylmethane and pyridine li.] chlorobenzene and no less than trichlorinated n-paraffins [6], a complex of zink chloride with o-dia-nizidine fill potassium bichromate [l2j, anthracene fl3, 14] 2,5-methoxy-4-amino-trans-stilbene [l5], benzyl ideneacetophenone fl6-l8] -thiophenylacetophenone,... 

The anthraquinone when subjected to reduction in the presence of tin metal and a mineral acid, such as hydrochloric acid, one of the ketonic oxygen atoms gets knocked out as a molecule of water leaving behind a tricyclic structure having only one ketonic function. The resultant modified version of anthraquinone is known as anthrone. 

Two forms of fo-ti tuber are used in traditional Chinese medicine, the dried tuber sheng he shou wu), which is the subject of this entry, and the processed tuber zhi he shou wu), which is the subject of a separate entry see previous entry). The processed tuber is used almost exclusively, while the dried tuber is not commonly used and is difficult to find commercially. The dried tuber contains stilbene glycosides and anthraquinone glycosides and is traditionally used for short periods of time as a stimulant laxative (Avula et al. 2007 Leung and Foster 1996 Zhang et al. 2006). 

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