Anthraquinones, changes when

The stereochemical complexity and chemical sensitivity of many dimeric pre-anthraquinones makes them less amenable to chromatographic identification than the anthraquinones themselves. Consequently, they have proved somewhat more difficult to use for the taxonomy of Phlegmacium (118, 265, 371, 509, 515, 617) than have the anthraquinones to the systematics of Dermocybe. Chemical instability of many pigments causes marked colour changes when sporophores of certain Phlegmacium species are stored in the herbarium (617),... 

Catalytic amounts of this addend (4 equiv relative to Cu) increase the selectivity of the allylic oxidation when TBHP is used as the oxidant. No change was observed with terf-butyl perbenzoate. This observation suggests a dichotomy in the mechanism of this reaction when using the two oxidants. Furthermore, in the absence of anthraquinone, a small negative nonlinear effect (78) is observed while in its presence, a small positive nonlinear effect appears. The reasons for this reversal are not clear, although the authors observed that low enantiopurity catalysts lead to turbid... 

The arylamino residue may be altered subsequently by sulfonation, halogena-tion, acylation, or by the Einhom reaction. Substitution of anthraquinone in the 5-, 6-, 7-, or 8-positions offers an additional possibility to change the characteristics of the dye. For instance, halogen atoms and sulfonic acid groups cause bath-ochromic effects that are most pronounced when the substituents are introduced in the b-position. The solubility of the 2,6- (or 2,7-) disulfonic acids is higher than that of the 2,5- (or 2,8-) series. 

When covalently attached to electron transfer active subunits, the DHA-VHF couple can facilitate chemical and physical switching of electronic properties, as a result of photochemically induced rearrangement accompanied by a change in the redox potential. An interesting example of such a switching system is the compound containing a dihydroazulene component and a covalently attached anthraquinone moiety.1311 This system is able to act as a multimode switch, assisted by various processes such as photochromism, reversible electron transfer, and protonation-deprotonation reactions (Scheme 8). 

Some organic molecules with OH dipoles behave similarly to water molecules when adsorbed on salt surfaces such as CaF2, BaCl2, or NaCl surfaces. On heating they do not desorb as such, but HF or HC1 evaporates and their ions are left behind as an adsorbed layer on the depleted salt surface. Many di- and polyhydroxy anthraquinones, like alizarin (138), behave in this way. The chemisorption reaction is accompanied by characteristic color changes, which could be studied by their absorption spectra, using completely transparent adsorbent layers as obtained by vacuum sublimation of these salts. 

Eleven 9,10-anthraquinones with various substituents, seven 1,4-naphthoquinones, 1,2-naphthaquinone and five 1,4-benzoquinones were used as QA. These quinones provide a series of RCs with a variation of the reaction exothermicity, - AG , from 0.11 to 0.9 eV. The rates of intraprotein electron transfer from various Qa to (BChl)J were found to be virtually temperature independent from 5 to 100 K and to decrease severalfold from 100 to 300 K. Only a small change of the rate upon the — AG° variation was found when reaction was made more exothermic than in the native RC. As the reaction was made less exothermic, the rate decreased notably without becoming temperature dependent. 

Changing Orientation. The addition of mercury changes the orientation in a number of aromatic sulfonation reactions. This is of great practical importance especially with anthraquinone, since in the presence of the catalyst the -sulfonate is formed almost exclusively, while without mw-cury only the 8-sulfonate is obtained. The -sulfonate, in fact, was unknown until as late as 1903 when the reaction was unintentionally conducted in the presence of mercury. This catalytic effect was subsequently studied extensively, with major conclusions as follows ... 

In the conversion of anthracene into anthraquinone, the para bond between the two carbon atoms involved in the oxidation is broken, but no change takes place in the benzene rings present in the compound. The synthesis of anthraquinone from phthalic anhydride confirms this view of its structure. When the anhydride is heated with benzene in the presence of a dehydrating agent, such as aluminium chloride, one molecule of water is lost and anthraquinone is formed —... 

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