Abstract:The radical anion of anthraquinone (AQ•−) has been generated by the reduction of anthraquinone (AQ) with sugars in aqueous alkaline solution. This appears to be the first time that the radical has been observed (esr spectrometry) in an entirely aqueous medium. Alkaline methanol solutions of AQ, when irradiated with light, yielded colourless solutions also exhibiting strong esr signals characteristic of. AQ•−.The ability of various carbohydrate and lignin preparations to reduce AQ, or to oxidize the reduced for… Show more
“…On this basis, the four transition states 4-7 are proposed for the interaction of enol ethers E and Z with bromine (Figure 1). The higher proximity of the carboxyalkyl group (*COOR1) to the double bond in the transition states 4 with respect to that in 6 and 5 with respect to that in 7 determines a greater electron-withdrawing field effect, which makes the double bond of 6 and 7 more reactive than that of 4 and 5, respectively.…”
A highly enantioselective synthesis of 2-alkyl-2-arylacetic acids, an important class of antiinflammatory agents, based on a new diastereoselective -bromination of homochiral acetals 1 and on the stereospecific silver-promoted rearrangement of the corresponding homochiral -bromo acetals 2 and 3, is reported. The new methodology represents a meaningful example of the use of tartaric acid as efficient and economic chiral auxiliary. The asymmetric bromination of 1 is of general character and occurs with very high diastereoselectivity, even at room temperature; a mechanism for the new reaction is proposed. The overall process has been successfully applied to the preparation of enantiomerically pure 2-alkyl-2-arylacetic acids, among them (2S)-(+)-2-(6-methoxy-2naphthyl)propanoic acid (Naproxen).
“…On this basis, the four transition states 4-7 are proposed for the interaction of enol ethers E and Z with bromine (Figure 1). The higher proximity of the carboxyalkyl group (*COOR1) to the double bond in the transition states 4 with respect to that in 6 and 5 with respect to that in 7 determines a greater electron-withdrawing field effect, which makes the double bond of 6 and 7 more reactive than that of 4 and 5, respectively.…”
A highly enantioselective synthesis of 2-alkyl-2-arylacetic acids, an important class of antiinflammatory agents, based on a new diastereoselective -bromination of homochiral acetals 1 and on the stereospecific silver-promoted rearrangement of the corresponding homochiral -bromo acetals 2 and 3, is reported. The new methodology represents a meaningful example of the use of tartaric acid as efficient and economic chiral auxiliary. The asymmetric bromination of 1 is of general character and occurs with very high diastereoselectivity, even at room temperature; a mechanism for the new reaction is proposed. The overall process has been successfully applied to the preparation of enantiomerically pure 2-alkyl-2-arylacetic acids, among them (2S)-(+)-2-(6-methoxy-2naphthyl)propanoic acid (Naproxen).
“…Anthraquinones have well-known antioxidant effects, even if they are not always potent [41]. Anthraquinone is used in the delignification of wood pulp for paper-making where its effect is thought to occur by electron transfer to a lignin molecule [42]. The antioxidant properties of anthraquinones are evident from the slow drying of oil paints that comprise red lakes.…”
Background: Color change in artworks has been commented on for centuries. Fading of watercolor pigments is a notable alteration. Pigments based on carminic acid are among those particularly prone to color loss, but the mechanism and factors are not well understood.
Results:We painted out three pigments prepared from the aqueous extract of carminic acid (CA) from Dactylopius coccus: the uncomplexed, and aluminium-and tin-complexed lakes. These were applied in a 2% gum Arabic solution to papers that were acidic, neutral or alkaline pH and exposed to accelerated light aging in a weatherometer. The comparative rate of fading was dependent on the complexation and on the pH of the substrate. On alkaline paper, the Al complex was least light stable, on neutral paper the three colorants responded similarly, and on acidic paper the tin complex was the least light stable. This is discussed in light of the published information on reactions and mechanism of color loss of CA.
“…In fact, several AQ species (like hydroxy‐anthraquinone) are naturally occurring products, often proposed for biological/medicinal applications. Moreover, the catalyzed oxidation/reduction of AQ derivatives has been widely applied for the alkaline delignification of wood, while AQ or more elaborated derivatives are used or proposed for the production of hydrogen peroxide (anthraquinone process) . However, the vast use of anthraquinoidic derivatives is found in dye production, since a range of colors maybe obtained, as a consequence of the chemical structure of 9,10‐anthraquinone .…”
A vinyl‐modified anthraquinone (AQ) derivative (Vinyl‐AQ) is synthesized through a palladium‐mediated Suzuki coupling reaction between vinylphenylboronic acid and 2‐chloromethylanthraquinone and, subsequently, copolymerized with N,N‐dimethylacrylamide (DMAM) through free radical copolymerization in organic solvent. The chemical structure of the resulting water‐soluble copolymer, P(DMAM‐co‐AQ), is verified using techniques such as proton nuclear magnetic resonance, attenuated total reflection‐infrared spectroscopy, thermogravimetric analysis, and UV–vis spectroscopy. The evolution of the oxygen scavenging abilities of aqueous P(DMAM‐co‐AQ) solutions after UV irradiation is monitored as a function of UV irradiation time, concentration of AQ moieties, and pH. The copolymer is proved an effective UV‐triggered oxygen scavenger, leading to dissolved oxygen contents below 1 ppm for the optimized experimental conditions. This behavior is related with the appearance of novel chemical species with interesting optical properties, as suggested by the respective evolution of the UV–vis absorption and photoluminescence spectra after UV irradiation.
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